Pressure Coefficient

Le refroidissement d'une pile à combustible (PEM), utilisée comme source d'énergie électrique dans le domaine de la traction automobile, fait apparaître un certain nombre de contraintes. Une des contraintes fortes se trouve être le refroidissement du coeur de pile, notamment du fait que le niveau de température est faible (environ 80 • C), mais aussi que la puissance thermique à évacuer est élevée. Cette étude s'intéresse à un refroidissement de la pile par l'évaporation interne d'un fluide ou par circulation d'un fluide monophasique. Le dispositif expérimental permet de vaporiser le fluide, le HFE7100, le long d'une plaque dont on souhaite mesurer les performances. Une technologie innovante de plaque présentant des bossages ou picots inversés est proposée. Ainsi, cette géométrie est très performante pour du refroidissement monophasique mais l'optimisation reste à faire en régime diphasique. Refroidissement monophasique / diphasique / pile à combustible / échange thermique / pertes de pression Abstract -Study of a new geometry for fuel cells cooling. Use of an embarked fuel cell, especially in a car, requires improving the cooling system efficiency. In such an application, one of the constraints is the low temperature (80 • C) and the important heat power to dissipate. A solution is to extract the latent heat of a boiling fluid. Another solution is to use a single phase flow fluid for cooling the system. For these reasons, heat transfer coefficient and frictional pressure drop are experimentally investigated. Single phase flow and flow boiling configurations of HFE7100 are tested in a vertical mini-channels device. An innovative technology is proposed. This geometry well performs for single phase flow and has to be improved for two-phase flow.

Use of an embarked fuel cell, especially in a car, requires improving the cooling system efficiency. In such an application, one of the constraints is the low temperature (80°C) and the important heat power to dissipate. A solution is to extract the latent heat of a boiling fluid. Another solution is to use a single phase flow fluid for cooling the system. For these reasons, heat transfer coefficient and frictional pressure drop are experimentally investigated. Single phase flow and flow boiling configurations of HFE7100 are tested in a vertical mini-channels device. An innovative technology is proposed. This geometry well performs for single phase flow and has to be improved for two-phase flow.

Carbon monoxide (CO) is a type of pollutant produced by industrial activities and is emitted through gas exhaust flues. Simulation activities are considered to provide a lot of information regarding the distribution of CO gas flow in the air. This paper will analyze the velocity and pressure distribution characteristics of CO gas to predict the accumulation of CO gas at various variations in the distribution distance of the gas. Simulation activities are carried out using SIMFLOW 3.1, a software capable of simulating fluid dynamics by emphasizing the ease of application. The simulation results show that the flow rate of CO gas is proportional to the amount of gas pressure generated at each distribution distance of the gas. The CO gas flow shows a fairly stable movement when identified at a distance of more than 30 m. This indicates that a mass of CO gas will be transmitted in the same amount over a distance of up to 70 m. The largest gas accumulation was obtained at a distance of 20...

of the chute blocks in stilling basins plays a significant role in size and type of these structures. One of the most influencing factors in the design of the blocks is the fluctuating pressure which may cause fatigue on the blocks. Despite investigations conducted by many researchers, there is not enough information about the pressure fluctuation around chute blocks in compacted stilling basins such as Saint Anthony Falls (SAF) basins. In this paper, the results of a naval experimental work and measurement of pressure fluctuations around chute blocks of SAF stilling basins are reported. The results show that the pressure fluctuations around the chute blocks cannot be overlooked in designing such structures. The variation of pressure fluctuation with Froude number of incoming supercritical flow at various faces of the chute block is reported, which shows an increasing trend of pressure fluctuation. It is also observed that the submergence of hydraulic jump will decreasingly affect the pressure fluctuations. The trend of variations will follow different patterns at the different faces of the block.

The use of numerical simulations for investigating machining processes is remarkably increasing because of the simulation cost is lower than the experiments and the possibility to analyze local variables such as pressures, strains, and temperatures is allowable. Process simulation is very hard from a computational point of view, since it frequently requires remeshing phases and very small time steps. As a consequence, the simulated cutting time is usually of the order of few milliseconds and no steady cutting conditions are generally achieved, at least as far as thermal conditions are concerned. Therefore, nowadays numerical prediction of cutting temperatures cannot be considered fully reliable. In the paper this issue was taken into account: a mixed Lagrangian-Eulerian numerical approach was utilized and the global heat transfer (film) coefficient at the tool-chip interface was derived through an inverse approach. Finally, the dependence of the film coefficient on pressure and temperature on the rake face was investigated.

This article considers the distribution of the pressure coefficient on the surface of a modular house model in order to further assess the possibility of operation of a thermosyphon solar collector integrated into the external protection. The experiment was planned to estimate the factors influencing the value of the aerodynamic coefficient. The results of experimental studies conducted in a wind tunnel are presented. The obtained graphical dependences were compared with the results of computer simulations and convergence was evaluated.

The present paper is centered on the study to understand the behavior of various surfaces of a 'Z' planshaped tall building under varying wind directions. For that purpose, computational fluid dynamics (CFD) package of ANSYS is used. The length scale is considered as 1:300. Force coefficients both in the along and across wind direction as well as the external surface pressure coefficients for different faces of the object building are determined and listed for wind incidence angle 0°-150°with increment of 30°. The wind flow pattern around the building showing flow separation characteristics and vortices are presented. The variation of wind pressure on different surfaces of the building is clearly shown by contour plots. The nature of deviation of external pressure coefficients along the height of the building as well as along the perimeter of the building for different wind angles of attack is presented. The force coefficient (C f ) along the X direction is extreme for 15°wind angle and along Y direction it is maximum for 60°angle of attack. Unsteady vortices are generated in the wake region due to a combination of positive and negative pressure in the windward and leeward faces, respectively.

This article considers the distribution of the pressure coefficient on the surface of a modular house model in order to further assess the possibility of operation of a thermosyphon solar collector integrated into the external protection. The experiment was planned to estimate the factors influencing the value of the aerodynamic coefficient. The results of experimental studies conducted in a wind tunnel are presented. The obtained graphical dependences were compared with the results of computer simulations and convergence was evaluated.

Effects of house design, orientation, and regional location on the natural ventilation of commercial, large-scale broiler poultry houses in the Northeastern and Southeastern farming regions of Botswana were assessed at full scale through computational fluid dynamics (CFD) simulations using the OpenFOAM CFD code. Local air change effectiveness (ACE), ε L was computed in a 0.25 m high animal occupation zone inside gable-, hoop-, and seesaw-roofed houses selected from three different farms per region. Observed airflow patterns and ε L values did not show regional dependence, whereas both were influenced by house orientation and, to a lesser extent, house design. Local ACE values obtained from the Northeastern farms ranged from 0.62 to 0.75, while in the Southeastern region values ranged from 0.56 to 0.90, with hoop-and gable-roofed structures yielding better ε L values than the seesaw-roofed structures from both regions. Simulations of theoretical perpendicular wind incidence (WI) angles for houses oriented to 140 and 135 • reduced their ACE values by 18.75 % and 0.53 %, respectively, indicating that their current orientation was optimal and allowing them to experience high WI. Houses oriented to 100 • and 105 • exhibited moderate improvements in ε L values of 5.84 % and 6.4 %, respectively, while houses oriented to 95 • and 90 • showed the greatest improvement in ε L values of 19.9 % and 37.52 %, respectively. Thus, site-specific orientation of poultry houses to 120 •-150 • would be recommended as it would allow for higher WI angles and better ε L in both geographical farming zones in Botswana. Furthermore, it may be concluded that design proposals to improve natural ventilation based on the hoop-and gable-roofed structuressupported by CFD simulations with experimental validationis warranted.

This paper presents an in-cylinder pressure pegging algorithm based on cyclic polytropic coefficient learning for combustion engines. In order to take the cycle-to-cycle variation of the polytropic coefficient into account in the incylinder measurement, an iterative learning algorithm is proposed to provide cyclic estimation of the polytropic coefficient and then with the estimation cyclic compensation method is proposed for the offset of in-cylinder pressure measurement. A comparative study of the proposed algorithm, the least-squares method (LSM) with a fixed polypropic coefficient and the nonlinear least-squares method (NLSM) with a variable polytropic coefficient is conducted using the simulated pressure data. Experimental validations are conducted on a six-cylinder gasoline engine at a motored condition and a steady fired operation condition.

We have determined the pressure coefficient of the direct band-gap energy of Al x Ga 1Ϫx As (0рxр0.35), by measuring the photoluminescence and photoluminescence-excitation spectra of 200-Å-wide Al x Ga 1Ϫx As/AlAs quantum wells with x values 0, 0.1, 0.18, 0.25, 0.3, and 0.35 at pressures up to 30 kbar. We have found that the pressure coefficient is independent of x within experimental uncertainties for x values in this range, clustering around 10.7 meV/kbar, a widely accepted value for bulk GaAs. This is in direct contrast to the only systematic measurement ͑at 300 K͒ in the literature, reported by Lifshitz et al. ͓Phys. Rev. B 20, 2398 ͑1979͔͒, which showed a nonlinear, nonmonotonic dependence of the direct band-gap pressure coefficient on the x values. An explanation for this difference is offered.

The functional box plot is generalized to provide a holistic view of the four dimensional space-time field data resulting from unsteady Computational Fluid Dynamics simulations. It displays the variation of five common statistics - minimum, first-quartile, median, third-quartile, and maximum - projected onto the three-dimensional spatial sub-space. Visual analysis using the generalized box plot is demonstrated for the unsteady flows past a swept cylinder and a wind turbine.

The recent development of computer-based tools with more efficient algorithms has allowed a substantial improvement in hydraulic turbine design. The definition of an initial geometry capable to assist certain characteristics of turbine performance is a first step for useful numerical turbine analysis. This paper presents an application of the minimum pressure coefficient criterion for axial-flow hydraulic turbines cascade geometry design. In recent works, the criterion was tested for axial fan and it was showed that it is suitable to define the initial geometry for machine design. The global parameters that supply the principal dimensions of the turbine are obtained from the literature as based upon statistical data of installed power plants. The grid of the simulation domain was generated with CFX-TURBO grid software package and the results were obtained using the commercial package Navier-Stokes 3-D CFX-TASCflow to analyze the fluid flow through blade runner. Using this procedure, a study was carried out on a small axial-flow turbine, specifically designed to operate in a small river in the Amazon region. An interpretation of the flow through the turbine's hydraulic channels is presented for nominal flow rate operation points. Finally, the results are evaluated to hydraulic efficiency prediction of blade runner turbines

New sets of equations have been constructed from the density‐pressure‐temperature and viscosity‐pressure‐temperature relationships to determine the rheology of synthetic lubricants at high pressure. A phase diagram was first plotted for the oils up to a pressure of 1.2 GPa and temperatures from 303 to 353 K using high‐pressure density experimental results and others. For the oils at temperatures of 313, 333, and 353 K, the high‐pressure viscosity experiment was done up to a viscosity of 104 Pa s and up to a pressure of 0.4 GPa. A relationship, based on free volume theory, between pressure and temperature with varying density and viscosity was proposed. It was found that the new equations from these relationships could predict the high‐pressure rheology more closely than those of previous researchers. Moreover, it was shown that the Ehrenfest equation or the gradient of the phase diagram is closely related to the expansion coefficient of free volume.

This work proposes a new model to evaluate the air changes per hour (ach) due to natural infiltrations in buildings. This modeling already exists at building scale, but the new model will implement the hourly ventilation load in a physical-based modeling for space heating and cooling in buildings at urban scale. The proposed improvement considers the wind and buoyancy effects in the calculation of hourly achs in a high-density urban context. A three-zone air flow lumped modeling is applied to describe the air flow in buildings; the air flow rate due to infiltrations is calculated depending only on leakages’ characteristics and pressure variations in various climate conditions. The non-linear equations system of mass and energy conservation is solved by an iterative procedure using the Newton-Raphson numerical method. Besides, two different  methodologies are compared to evaluate the external dynamic and static pressure conditions on building façades: experimental values (pressure coefficients Cp) and CFD simulations. For the latter, the air flow field in the urban canyons is described by the windy conditions and by imposing a temperature gradient due to solar irradiation between the windward
and leeward facades. This methodology is applied to three urban canyons in Turin, with typical aspect ratios and orientations for some local climate conditions considering both heating and cooling seasons. Comparing the results of hourly ach obtained from the Cp method, the CFD technique allows to modulate the ach considering the impact of the canyon dimension, wind and buoyancy effect of non-isothermal condition,  in varying the wind speed on the façades of buildings for different scenarios.  t also overcomes the limit of field of applications of Cp, especially in high-density built urban environments. The encouraging results of this work will  ead to future developments of the three-zone lumped model and its numerical solution techniques.

Pressure effect on Hall coefficient RII was investigated in YI-xCaxBa2Cu3Ck, (x-O.15 and 0.20) without Cu-O chain. No change in RH was observed under pressure up to 12kbar; no pressure-induced change occurs in the carrier density. The pressure-induced change in the cartier density does not occur when the oxygen atoms in the Cu-O chain is hard to displace by annealing or applying pressure.

A new wind testing facility, the Wind-induced Damage Simulator (WDS), was designed and built at the University of Ottawa. The new facility is capable of generating extreme wind conditions and can achieve high pressure testing environment for scaled models as well as for full-scale structural elements such as: roofs, windows and curtain walls. The WDS system has dimensions of 3.65 m x 3.65 m x 3.0 m and has 20 circular inlet openings on the four lateral walls. The outlet of the box has a diameter of 300 mm, is at the center of the roof and it is connecting to a powerful industrial blower through a steel duct. Scaled models, 1:30 and 1:40 of the Silsoe cube, which is a basic shape structure was and a total of 42 pressure taps were installed on its surface. Pressure measurements were performed for unidirectional and shear wind flow conditions determined by activating the first and second inlets at the corner of the WDS. Also, different positions of the Silsoe cube model were investigat...

Studies on the mechanisms of natural ventilation in livestock buildings are reviewed and influences on discharge and pressure coefficients are discussed. Compared to studies conducted on buildings for human occupation and industrial buildings which focus on thermal comfort, ventilation systems, indoor air quality, building physics and energy etc., our understanding of the mechanisms involved in natural ventilation of livestock buildings are still limited to the application of the orifice equation. It has been observed that the assumptions made for application of the orifice equation are not valid for wind-induced cross ventilation through large openings. This review identifies that the power balance model, the concept of stream tube and the local dynamic similarity model has helped in the fundamental understanding of wind-induced natural ventilation in buildings for human occupation and industrial buildings. These concepts have distinguished the flow through large openings from that of 'cracks' (i.e. small openings), which is where the orifice equation is normally used for prediction of airflow rate. More field measurements on the effect of wind turbulence on ventilation rate need to be encouraged, particularly under conditions where the mean pressure differences through building openings are much lower than the fluctuations of pressure differences. Research on bidirectional flow that occurs at openings is also limited.

The effect of starvation in mixed elastohydrodynamic lubrication (EHL) regime is studied. Numerical simulations are conducted for both line and point (elliptical) contacts with the consideration of the surface roughness. The degree of starvation is linked directly to the reduction in the lubricant mass flow rate. Results are presented to gain insight on the influence of starvation on the film thickness as well as the interaction between the surface asperities. Extensive sets of simulation results are used to quantify the effect of starvation in the EHL of rough surfaces. Expressions are developed to predict the percentage of the load carried by the surface asperities (asperity load ratio) as well as the reduction of the central and minimum film thickness in the starved mixed EHL.

An engineering approach is introduced for estimating the traction coefficient and the wear rate in elastohydrodynamic lubrication of rough surfaces without the need of extensive numerical simulations. The method suggested by Tian and Kennedy is extended to the mixed EHL to estimate the temperature rise. This temperature rise is then used together with the formulas for the film thickness and asperity load to evaluate the traction coefficient and the wear rate for different input conditions. The results from this method are compared to those from numerical simulations.

Olfactory flow in fishes is a little-explored area of fundamental and applied importance. We investigated olfactory flow in the pike, Esox lucius, because it has an apparently simple and rigid nasal region. We characterised olfactory flow by dye visualisation and computational fluid dynamics, using models derived from X-ray micro-computed tomography scans of two preserved specimens. An external current induced a flow of water through the nasal chamber at physiologically relevant Reynolds numbers (200 -300). We attribute this externallyinduced flow to: the location of the incurrent nostril in a region of high static pressure; the nasal bridge deflecting external flow into the nasal chamber; an excurrent nostril normal to external flow; and viscous entrainment. A vortex in the incurrent nostril may be instrumental in viscous entrainment. Flow was dispersed over the olfactory sensory surface when it impacted on the floor of the nasal chamber. Dispersal may be assisted by: the radial array of nasal folds; a complementary interaction between a posterior nasal fold and the ventral surface of the nasal bridge; and the incurrent vortex. The boundary layer could delay considerably (up to ~ 3 s) odorant transport from the external environment to the nasal region. The drag incurred by olfactory flow was almost the same as the drag incurred by models in which the nasal region had been replaced by a smooth surface. The boundary layer does not detach from the nasal region. We conclude that the nasal bridge and the incurrent vortex are pivotal to olfaction in the pike.

The article presents an experimental study, which has been carried out in an environmental wind tunnel to measure the mean pressures and pressure differences at inlet and outlet of various openings of a naturally ventilated classroom model of a school building located near an urban roadway in the city of Delhi. The wind pressure coefficients have been measured and analyzed for different wind incidence angles and for varying classroom opening configurations representing the change in behavior of building occupants in different seasons of the year. The article also presents the results of a CFD modeling carried out to estimate the wind velocity and turbulent intensity in and around the classroom model to understand the actual airflow pattern inside the classroom. The present study is an effort to understand the occurrence of ventilation in naturally ventilated buildings and finally to evaluate the indoor air quality in such buildings.

The wind load and pressure on a tall hexagonal structure altered as the apertures changed in this study. In various conditions, wind angles ranging from 0 to 90 degrees with a 30-degree gap are being used. The distance between the interference building and the model building was gradually raised from 50mm to 200mm at 50mm intervals. At a scale of 1:500, the main building model was studied. The ANSYS CFX package's validity was also tested using a rigid model with dimensions of 100mm x 100mm and a height of 700mm. The k-ε-turbulence model was utilised in the investigation, which was conducted using Computational Fluid Dynamics (CFD) and the ANSYS CFX software package. According to the analysis, changing the percentage of opening area has an influence on building stability because it affects the pressure on the leeward and windward faces. Contours and vortex formation were used to highlight the relationship between different scenarios. As the distance between the interference and m...

Wind induced damage on low-rise buildings with complex roof geometry is common in coastal areas of USA, such as Florida and Louisiana. Available design codes provide information about the design of regular roof geometries (e.g. hip/gable roofs), but refer to wind tunnel modelling for complex roof geometries. Due to time and financial constraints physical modelling may not always be possible to carry out. Computational modelling through Large Eddy Simulation (LES) has been used successfully for several wind engineering applications. This paper presents comparisons between LES and previously obtained wind tunnel data of mean and peak pressure coefficients on a low rise building with complex roof geometry. Two different cases, namely: isolated building and the effect of neighbouring buildings have been considered for the most critical wind direction of 135 degrees. Results show that the mean pressure coefficients on the low rise building roof for the case with adjacent buildings were s...

SAINI, ADITYA. Leading-Edge Flow Sensing for Aerodynamic Parameter Estimation. (Under the direction of Dr. Ashok Gopalarathnam.) The identification of inflow air data quantities such as airspeed, angle of attack, and local lift coefficient on various sections of a wing or rotor blade provides the capability for load monitoring, aerodynamic diagnostics, and control on devices ranging from air vehicles to wind turbines. Real-time measurement of aerodynamic parameters during flight provides the ability to enhance aircraft operating capabilities while preventing dangerous stall situations. This thesis presents a novel Leading-Edge Flow Sensing (LEFS) algorithm for the determination of the air-data parameters using discrete surface pressures measured at a few ports in the vicinity of the leading edge of a wing or blade section. The approach approximates the leading-edge region of the airfoil as a parabola and uses pressure distribution from the exact potential-flow solution for the parabola to fit the pressures measured from the ports. Pressures sensed at five discrete locations near the leading edge of an airfoil are given as input to the algorithm to solve the model using a simple nonlinear regression. The algorithm directly computes the inflow velocity, the stagnation-point location, section angle of attack and lift coefficient. The performance of the algorithm is assessed using computational and experimental data in the literature for airfoils under different flow conditions. The results show good correlation between the actual and predicted aerodynamic quantities within the pre-stall regime, even for a rotating blade section. Sensing the deviation of the aerodynamic behavior from the linear regime requires additional information on the location of flow separation on the airfoil surface. Bio-inspired artificial hair sensors were explored as a part of the current research for stall detection. The response of such artificial micro-structures can identify critical flow characteristics, which relate directly to the stall behavior. The response of the microfences was recorded via an optical microscope for flow over a flat plate at different freestream velocities in the NCSU subsonic wind tunnel. Experi

Building energy simulation (BES) and Airflow network (AFN) programs generally incorporate wind pressure coefficients (Cp) estimated from secondary sources, namely data bases or analytical models. As these coefficients are influenced by a wide range of parameters, it is difficult to obtain reliable Cp data. This leads to uncertainties in BES-AFN models results, especially for naturally ventilated building studies, where air change rate which strongly depends on Cp, is a key value for thermal comfort and energy consumption results. This study focuses on naturally ventilated buildings in tropical climate and presents an alternative approach to estimate wind pressure coefficient. Computational fluid dynamics (CFD) simulations are performed to calculate wind-driven airflow rates at building opening level. Then wind pressure coefficient difference ΔCp is calculated from large opening equation to be used as input data in BES-AFN program. Numerical simulations are performed for various wind directions on a typical cross-ventilated isolated building and a more complex building with opposite large openings. CFD results of wind pressure coefficient difference and airflow rate are compared to those obtained from AFN model using two different Cp sources. The results show that the calculated values vary greatly depending on the method used and highlight that an accurate estimation of wind pressure coefficient is a key parameter for evaluating natural ventilation in buildings.

The hydrostatic pressure dependence of photoluminescence, dEPL/dp, of InxGa1−xN epilayers has been measured in the full composition range 0<x<1. Furthermore, ab initio calculations of the band gap pressure coefficient dEG/dp were performed. Both the experimental dEPL/dp values and calculated dEG/dp results show pronounced bowing and we find that the pressure coefficients have a nearly constant value of about 25 meV/GPa for epilayers with x>0.4 and a relatively steep dependence for x<0.4. On the basis of the agreement of the observed PL pressure coefficient with our calculations, we confirm that band-to-band recombination processes are responsible for PL emission and that no localized states are involved. Moreover, the good agreement between the experimentally determined dEPL/dp and the theoretical curve of dEG/dp indicates that the hydrostatic pressure dependence of PL measurements can be used to quantify changes of the band gap of the InGaN ternary alloy under pressure,...

Article history: Received 24 June 2019 Received in revised form 21 August 2019 Accepted 2 October 2019 Available online 13 October 2019 Numerical investigation of a non-circular cylinder (D-shaped bluff body) of fore body, geometrical effects on the drag as well as on the flow-field were simulated at the subcritical flow regime at a velocity of 26.84 m/s. The non-circular cylinder (D-shaped model) front surface for a positive pressure of the unsteady vortex generation in the near wake, the square plate was attached upstream of the non-circular cylinder as the base model. The forebody modifies the streamlines that separate from its edges to attach smoothly onto the front face shoulders of the main body, thereby converting the bluff body into an equivalent streamlined body, resulting in minimum drag. The height of the forebody (B1) is 25 mm, and the length of the front body (L2), was in the range from 0.25B2 to 1.75B2. The results obtained from the simulation are compared with the exp...

In the present investigation the distribution of mean velocity, static pressure and total pressure are experimentally studied on an annular curved diffuser of 30° angle of turn with an area ratio of 1.283 and centerline length was chosen as three times of inlet diameter. The experimental results then were numerically validated with the help of Fluent and then a series of parametric investigations are conducted with same centre line length and inlet diameter but with different area ratios varying from 1.15 to 3.75. The measurements were taken at Reynolds number 2.25 x 105 based on inlet diameter and mass average inlet velocity. Predicted results of coefficient of mass averaged static pressure recovery (30%) and coefficient of mass averaged total pressure loss (21%) are in good agreement with the experimental results of coefficient of mass averaged static pressure recovery (26%) and coefficient of mass averaged total pressure loss (17%) respectively. Standard k-ε model in Fluent solve...

In order to estimate the wind loads on circular cylindrical shell structures, the pressure coefficient as a function of the Reynolds number is given for an isolated cylinder in Eurocode 1-Part 2-4 : Actions on structures-Wind actions. As cylinders are often placed in groups and the configuration of these groups largely influences the pressure distribution around the cylinders, a computation of the wind flow provides a more realistic estimation of the pressure coefficients. First, the transient 2D turbulent air flow around a single cylinder at a Reynolds number of 1.24 ×10 7 is computed using the SST turbulence model and the results are compared with the pressure coefficients in Eurocode 1 and with experimental data. The minimum pressure coefficient is underestimated, while the base pressure coefficient is slightly overestimated. Unsteady simulations are performed for the flow around a group of 2 by 2 and of 8 by 5 cylinders. Vortex shedding occurs both from the group as a whole, and from individual cylinders. The group configuration drastically changes the time-averaged pressure distribution around the cylinders. High values of suction are present at the location of the small gaps between the cylinders and upstream of the separation points of the cylinders on the side corners of the groups. The cylinders at the borders of the groups experience high drag or lift forces, while these forces are considerably lower in the middle of the group.

In order to estimate the wind loads on circular cylindrical shell structures, the pressure coefficient as a function of the Reynolds number is given for an isolated cylinder in Eurocode 1-Part 2-4 : Actions on structures-Wind actions. As cylinders are often placed in groups and the configuration of these groups largely influences the pressure distribution around the cylinders, a computation of the wind flow provides a more realistic estimation of the pressure coefficients. First, the transient 2D turbulent air flow around a single cylinder at a Reynolds number of 1.24 ×10 7 is computed using the SST turbulence model and the results are compared with the pressure coefficients in Eurocode 1 and with experimental data. The minimum pressure coefficient is underestimated, while the base pressure coefficient is slightly overestimated. Unsteady simulations are performed for the flow around a group of 2 by 2 and of 8 by 5 cylinders. Vortex shedding occurs both from the group as a whole, and from individual cylinders. The group configuration drastically changes the time-averaged pressure distribution around the cylinders. High values of suction are present at the location of the small gaps between the cylinders and upstream of the separation points of the cylinders on the side corners of the groups. The cylinders at the borders of the groups experience high drag or lift forces, while these forces are considerably lower in the middle of the group.

In this study, the static pressure distribution over the cylinder model having a circular finite geometry have been determined experimentally. In the experiments open circuit and suction type wind tunnel has been used. The wind tunnel test section has 20 cm x 21 cm cross section and 48 cm length, and maximum air flow velocity is 15 m/s. The experiments have been carried out at the air flow rates changing an increase of 5%. The variation of the static pressure over the circular finite cylinder model with air velocity, and the variation of the static pressure coefficient with Reynolds number have been investigated. In the experiments, occurrence of D'Alembert's paradox over the circular finite cylinder model has been determined. Because of the lower air flow velocity of the studied wind tunnel, low Reynolds values has been achieved. For this reason, the higher capacity wind tunnel has been needed for obtaining stable static pressure coefficient (Cp ) values.

The effect of laser marking process on the tribological behaviour of ISO 5832-1 austenitic stainless steel (SS) on the friction coefficient and wear volume using ball-cratering wear tests was evaluated in this work. The laser marking process was carried out with a nanosecond optical fiber ytterbium laser at four different pulse frequencies. For comparison reasons, surfaces without laser treatments were also evaluated. A phosphate buffer solution (PBS) was used as lubricant. The wear tests were carried out during 10 min with PBS drip, solid spheres of AISI 316L SS with 1 inch in diameter and of 52-100 chrome steel, with 2 mm in diameter, were used as counter-bodies. The results indicated that the tribological behaviour is influenced by the laser marking process parameters used, and the wear rate is dependent of the normal force and the type of sphere.

This chapter evaluated the influence of laser texturing process on the tribological behavior of the ISO 5832-1 austenitic stainless steel (SS). The friction coefficient and wear were determined using ball-cratering wear tests. The laser texturing process was carried out with a nanosecond optical fiber ytterbium laser at four different pulse frequencies. Cytotoxicity tests were carried out to determine if laser texturing affects the biomaterial biocompatibility. For comparison reasons, pristine surfaces were also evaluated. The results indicated that the wear volume and friction coefficient were reduced after laser texturing. The samples were considered noncytotoxic according to the biocompatibility tests as the laser texturing process did not decrease cell's viability.

An unsteady molten steel meniscus flow sometimes occurs in the continuous casting mold. When it impinges on the immersion nozzle, a severe vertical pressure difference is induced on the outer surface of the nozzle. Mold powder entrapment near the immersion nozzle is closely associated with the pressure difference. The use of an elliptic immersion nozzle is expected to effectively lower the difference, and accordingly, suppress the mold powder entrapment. The pressure difference around the elliptic immersion nozzle however is not quantitatively known yet. In this study it was numerically calculated by the vortex method over a wide aspect ratio range of the nozzle for two types of unsteady meniscus flows. The validity of the numerical results was confirmed from a comparison with previous results obtained from cold model experiments.

W pracy przedstawiono wyniki i analizę badań modelowych przeprowadzonych w tunelu aerodynamicznym w odniesieniu do opływu pojedynczego walca kołowego. Wyniki dotyczą zmian wartości zredukowanego współczynnika średniego ciśnienia na powierzchni modelu oraz jego odchylenia standardowego. W badaniach analizowano 6 przypadków struktury napływającego wiatru opisanej za pomocą funkcji pionowego profilu średniej prędkości wiatru, pionowego profilu intensywności turbulencji oraz funkcji gęstości widmowej mocy. Wysokość badanego modelu oraz jego średnica wynosiły odpowiednio H = 100 cm i D = 20 cm.

The paper deals with results of measurements which have been carried out in the wind tunnel. Vertical, fixed prism of the cross-section dimensions 10 cm x 20 cm was the object of the experiment. Distributions of mean wind pressure coefficient on the surface of the prism were accepted as results presentation. The following parameters of the wind structure were analysed: vertical mean wind speed profile, turbulence intensity profile, power spectral density functions with respect to their influence on pressure coefficient values. Changes of the angle of wind attack were taken into consideration.

Heat transfer in flow across bank of tubes is of particular importance in the design of heat exchangers. Heat exchangers are found in numerous industrial applications, such as steam generation in a boiler or air cooling in the coil of an air conditioner. The Zakauskas’s correlation from the experimental data is more popular method that used to design of cross flow of heat exchanger. However, due to optimization process and more efficiency, several empirical equations were generated through the analytical and CFD methods. Hence, this paper was intended to perform a comprehensive study to analyze the heat transfer calculation of cross flow heat exchanger by using several methods in which it has been reported. Among of four methods are analyzed, the analytic method, normalization equations from CFD and Grimison’s correlation have good agreement to used for design of cross flow heat exchanger with the compact and non-compact configuration, while correlation of Zakauskas is only suitable...

Mine backfilling is a technique that has been used for decades in Canada and across the globe [1, 2]. This method has several advantages such as stabilizing the drifts and stopes of a mine and increasing worker safety. Backfilling serves to fill excavations in a mine and allows ore to be extracted more completely because the underground excavations have better support. Environmental benefits result from the use of tailings as backfill material: problems related to the disposal of surface tailings can be reduced as substantial quantities of potentially polluting tailings can be returned underground. This backfill material generally consists of a mixture of tailings, water and cement. The backfilling process has several technical aspects that interact with one another. This includes the hydrogeology, mineralogy and geochemistry of both the host rock and backfill material as well as the mechanical behavior of these two media. Mechanical

An analysis of the external pressure coefficient on the surface of a ruin in different flow directions is presented. The ruin has almost cube-like proportions with an open roof plane and a destroyed corner. Flow simulations were performed using 3D Time Steady RANS and compared with experimental results from the boundary layer wind tunnel at the Slovak University of Technology in Bratislava. The optimal turbulence model and internal mesh settings were selected based on their statistical evaluation. For an evaluation of the critical directions of the wind flow around the ruin, the values of the external wind pressure coefficient were obtained from the selected calculation model and settings.

Mean wind pressure coefficients on surfaces of a gable-roofed low-rise building are measured in a wind tunnel test and calculated with CFD technique. The errors between these two sets of data are shown and analyzed by detailed comparison. Wind pressure coefficients on windward wall agree well with each other. On leeward wall and on an area with larger pressure grads, the differences between those two data are larger. The differences at other location are acceptable.

Pour atteindre des champs magnétiques plus intenses que ceux produits commercialement avec des aimants supraconducteurs, des bobines de champs à base d'alliage de cuivre sont développées dans quelques installations de champs magnétiques intenses. A Grenoble, une installation d'une puissance électrique de 24 MW permet de produire des champs continus jusqu'à 37 T dans un diamètre de 34 mm. Une augmentation de puissance à 30 MW est prévue pour être opérationnelle en 2022. Un aimant pour champs magnétiques intenses est un archétype d'échangeur compact aux caractéristiques extrêmes. Des flux de chaleur atteignant 10 MW.m-2 sont traités par un refroidissement par eau monophasique avec des vitesses de passages atteignant 30 m.s-1. Les canaux de refroidissement sont caractérisés par des diamètres hydrauliques de 200 à 1800 µm et des longueurs de 30 mm à 430 mm. Une perte de pression de 20 bars se développe entre l'entrée et la sortie de l'aimant pour champs intenses, le coefficient de transfert à la paroi des bobines atteint h=10 5 W.m-2 .K-1. En 2018, 15 GWh d'énergie électrique ont été injectés dans les aimants pour champs intenses de Grenoble. Cette énergie est intégralement transformée en chaleur fatale rejetée dans la rivière voisine. Un des projets du laboratoire est d'injecter une partie de ces calories dans le réseau de chaleur de l'agglomération grenobloise. La température de sortie de l'aimant est aujourd'hui au maximum de 40°C, température au-dessous de celle requise par le réseau de chaleur. L'utilisation d'une pompe à chaleur pour relever la température est donc nécessaire. Pour améliorer le modèle économique et les performances environnementales du projet, une solution est d'augmenter la température de sortie de l'aimant pour minimiser les coûts électriques associés aux pompes à chaleur. Pour cela nous devons diminuer le débit d'alimentation de l'aimant qui est actuellement 300 l.s-1 pour 24 MW et augmenter Mots clefs: transfert thermique, hydrodynamique, mini canaux , ébullition nucléée, transfert de chaleur intense, récupération de chaleur fatale, champs magnétiques intenses, réseau de chaleur urbain.

Pour atteindre des champs magnétiques plus intenses que ceux produits commercialement avec des aimants supraconducteurs, des bobines de champs à base d'alliage de cuivre sont développées dans quelques installations de champs magnétiques intenses. A Grenoble, une installation d'une puissance électrique de 24 MW permet de produire des champs continus jusqu'à 37 T dans un diamètre de 34 mm. Une augmentation de puissance à 30 MW est prévue pour être opérationnelle en 2022. Un aimant pour champs magnétiques intenses est un archétype d'échangeur compact aux caractéristiques extrêmes. Des flux de chaleur atteignant 10 MW.m-2 sont traités par un refroidissement par eau monophasique avec des vitesses de passages atteignant 30 m.s-1. Les canaux de refroidissement sont caractérisés par des diamètres hydrauliques de 200 à 1800 µm et des longueurs de 30 mm à 430 mm. Une perte de pression de 20 bars se développe entre l'entrée et la sortie de l'aimant pour champs intenses, le coefficient de transfert à la paroi des bobines atteint h=10 5 W.m-2 .K-1. En 2018, 15 GWh d'énergie électrique ont été injectés dans les aimants pour champs intenses de Grenoble. Cette énergie est intégralement transformée en chaleur fatale rejetée dans la rivière voisine. Un des projets du laboratoire est d'injecter une partie de ces calories dans le réseau de chaleur de l'agglomération grenobloise. La température de sortie de l'aimant est aujourd'hui au maximum de 40°C, température au-dessous de celle requise par le réseau de chaleur. L'utilisation d'une pompe à chaleur pour relever la température est donc nécessaire. Pour améliorer le modèle économique et les performances environnementales du projet, une solution est d'augmenter la température de sortie de l'aimant pour minimiser les coûts électriques associés aux pompes à chaleur. Pour cela nous devons diminuer le débit d'alimentation de l'aimant qui est actuellement 300 l.s-1 pour 24 MW et augmenter Mots clefs: transfert thermique, hydrodynamique, mini canaux , ébullition nucléée, transfert de chaleur intense, récupération de chaleur fatale, champs magnétiques intenses, réseau de chaleur urbain.

The article deals with the numerical analysis of the wind pressure distribution on a group of two high-rise buildings of different shape for different wind directions. The first building has the shape of a circular cylinder and the second was created by a combination of semicircles and a longitudinal member. The floor plan of the second building was similar to the letter S. The simulations were realized as 3D steady RANS. CFD results were compared with experimental measurements in the wind tunnel of the Slovak University of Technology in Bratislava. The results were processed using statistical methods such as correlation coefficient, fractional bias and fraction of data within a factor of 1.3, which determined the most suitable CFD model. The purpose of the present article was to verify the distribution of the external pressure coefficient on scale models at a scale of 1:350, which are located in the Atmospheric Surface Layer (ASL). In numerical modeling, the most important thing wa...

la taille du confinement des canaux de circulation des fluides diphasiques modifie la structure de l'écoulement et intensifie le phénomène de transfert de chaleur. Cet article présente les résultats d'une étude expérimentale sur la condensation de la vapeur d'eau dans un seul micro-canal transparent. Différents régimes d'écoulement périodiques sont identifiés. Une analyse locale de certains phénomènes physiques est menée en se basant sur des visualisations de l'écoulement et une procédure de traitement d'images.

La ventilación natural se ha ganado protagonismo en los últimos tiempos como una medida de ahorro de energía para edificios. Los dos principios fundamentales de ventilación natural son el tiro natural por diferencia de temperatura, y la fuerza del viento. El artículo pretende analizar la aerodinámica de los captadores y extractores de viento mediante fluido-mecánica computacional, optimizando las geometrías de estos elementos, y dando como producto del trabajo un modelo simplificado para poder tenerlos en cuenta el cálculo aeráulico de las instalaciones de ventilación y climatización de los edificios. Concretamente, se caracteriza una base de geometrías de captación de viento, y se elabora una guía para el diseño de geometrías de extracción ofreciendo varias de ellas como producto del trabajo realizado.