Internal Flow

Measurement and Modeling of Channel Wall Vibration Subjected to Internal Bubbly Flow 1 MINGMING ZHANG, JOSEPH KATZ, ANDREA PROSPERETTI, Johns Hopkins University -The effect of a bubbly flow, injected into both a square and rectangle channels, on channel wall vibrations is studied experimentally and theoretically. The vibrations are measured under various gas void fractions, bubble diameters and channel dimensions. A theoretical model, based on a waveguide theory and bubble dynamics, is developed to predict the dominant frequencies in vibration spectra, the corresponding decay rates and propagation phase speeds. Results show that, compared with no bubble case, the presence of bubbles substantially enhances the power spectral density of vibrations, by up to 27 dB in a square channel and 37 dB in a rectangular channel. The origin of enhanced vibrations is attributed to the excitation of the streamwise propagating pressure waves, created by an initial acoustic energy generated during bubble formation. The model predicts very well the magnitudes and trends of the dominant spectral frequencies, the corresponding decay rates and phase speeds. The frequency, attenuation and phase speed decrease substantially with increasing void fraction but slightly with increasing diameter.

NASA Glenn hosted the Seals/Secondary Air System Workshop on October 25-26, 2000. Each year NASA and our industry and university partners share their respective seal technology developments. We use these workshops as a technical forum to exchange recent advancements and "lessons-learned" in advancing seal technology and solving problems of common interest. As in the past we are publishing two volumes.

For high-performance foiling yachts, cavitation is often a limiting factor for take-off and top speed. The present work investigates solutions to control the onset of cavitation thanks to a combination of leading edge and trailing edge flaps. Numerical and experiments in a hydrodynamic tunnel are conducted in order to assess the effect of specific geometric parameters on the hydrodynamic performance and cavitation inception. The hydrofoils are manufactured using an additive 3D printing technique and tested in the cavitation tunnel of IRENav at an inflow velocity of 6.67 m∕s (𝑅𝑒 = 10 6 ). The effect on the hydrodynamic performances and cavitation buckets of a 70% chord trailing edge flap and a 20% chord leading edge flap of NACA 0012 is investigated. The results show that the lift coefficient increases and the cavitation bucket shifts up and decreases with the flaps deflection. The experimental results are in good agreement with the numerical ones by highlighting the capacity of the flaps to modify both the operating domain and the cavitation bucket of the hydrofoil. Eventually, the PLA 3D printed foils prove to be a fast, unexpensive and reliable technologies for cavitation studies.

Authors : Fatiha Mohammed Arab, Benoit Augier, Francois Deniset, Pascal Casari, Jacques Andre Astolfi Abstract : For the top high performance foiling yachts, cavitation is often a limiting factor for take-off and top speed. This work investigates solutions to delay the onset of cavitation thanks to structural morphing. The structural morphing is based on compliant leading and trailing edge, with effect similar to flaps. It is shown here that the commonly accepted effect of flaps regarding the control of lift and drag forces can also be used to postpone the inception of cavitation. A numerical and experimental study is conducted in order to assess the effect of the geometric parameters of hydrofoil on their hydrodynamic performances and in cavitation inception. The effect of a 70% trailing edge and a 30% leading edge of NACA 0012 is investigated using Xfoil software at a constant Reynolds number 106. The simulations carried out for a range flaps deflections and various angles of atta...

Gas turbines are not generally designed for operation with a particle laden inlet flow but, in fact, are commonly operated in unclean environments resulting in dirt, sand, and other debris ingestion. In addition to the negative effects within the main gas path, for aeroengines these particles are pulled into the coolant system where they can clog cooling passages and erode internal surfaces. Unlike previous research that focused on deposition and erosion within the main gas path, this study evaluated blocking in a double wall liner whereby both impingement and film-cooling holes were simulated. Double wall liners are commonly used in the combustor and turbine for combined internal and external cooling of metal components. Specifically, sand blockages were evaluated through comparisons of measured flowrates for a particular pressure ratio across the liner. Four liner geometries were tested whereby the coolant hole size and orientation were varied in test coupons. At ambient temperature, blocking was shown to be a function of the impingement flow area. A significant rise in blocking was observed as sand and metal temperatures were increased. The overlap between the impingement and film-cooling holes was also found to have a significant effect.

As part of an effort to understand the conditions for the ignition of cryogenic propellants in the low pressure environment, we conducted a research of internal flow of cryogenic jet. In this paper, the experimental investigation was exerted focusing on the qualitative morphology study of the cryogenic flow inside the jet injectors. The test facilities were carefully designed and allow for visualization and characterization of the flow. The results show a strong dependence of mass flow rate on the fluid temperature. The two-phase flow was observed even for a long time chilling down of the injector. The Jacob number is proved to be a good indicator for the flow regimes, and the bubbles are present in the flow every time. The injector geometry has an influence on the flow rate, with the tapered injector demonstrating a higher flow rate than the sharp one.

ABSTRACTMeasurements of diurnal diameter variations of the xylem and phloem are a promising tool for studying plant hydraulics and xylem–phloem interactions in field conditions. However, both the theoretical framework and the experimental verification needed to interpret phloem diameter data are incomplete. In this study, we analytically evaluate the effects of changing the radial conductance between the xylem and the phloem on phloem diameter variations and test the theory using simple manipulation experiments. Our results show that phloem diameter variations are mainly caused by changes in the radial flow rate of water between the xylem and the phloem. Reducing the hydraulic conductance between these tissues decreases the amplitude of phloem diameter variation and increases the time lag between xylem and phloem diameter variation in a predictable manner. Variation in the amplitude and timing of diameter variations that cannot be explained by changes in the hydraulic conductance, c...

We report in this paper the evolution of a physically-based drop size-distribution coupling the Maximum Entropy Formalism and the Monte Carlo method to solve the distribution equation of a spray. The atomization is performed by a new Spray On Demand (SOD) device which exploits ultrasonic generation via a Faraday instability. The Modified Hamilton's principle is used to describe the fluid structure/interaction with a vibrating micro-channel conveying fluid excited by a pointwise piezoactuator. We combine to the fluid/structure description a physically based approach for predicting the drop-size distribution within the framework of the Maximum Entropy Formalism (MEF) using conservation laws of energy and mass coupling with the three-parameter generalized Gamma distribution. The prediction and experimental validation of the drop size distribution of a new Spray On Demand print-head is performed. The dynamic model is shown to be sensitive to operating conditions, design parameter and physico-chemical properties of the fluid and its prediction capability is good. We also report on a model allowing the evolution of drop sizedistribution. Deriving the discrete and continuous population balance equation, the Mass Flow Algorithm is formulated taking into account interactions between droplets via coalescence. After proposing a kernel for coalescence, we solve the time dependent drop size distribution using a Monte Carlo Method which is shown to be convergent. The drops size distribution upon time shows the effect of spray droplets coalescence.

Complying with emission requirements and fuel consumption efficiency are the points which drive any development of internal combustion engine. Refinement of the process of combustion and mixture formation, together with in-cylinder flow refinement, is a requirement, valves and piston bowl and intake exhaust port design optimization is essential. In order to reduce the time for design optimization cycle it is used Computational Fluid Dynamics (CFD). Being time consuming and highly costly caring out of experiment using flow bench testing this methods start to become less utilized. Air motion inside the intake manifold is one of the important factors, which govern the engine performance and emission of multi-cylinder diesel engines. Any cold flow study on IC is targeting the process of identifying and improving the fluid flow inside the ports and the combustion chamber. This is only the base for an optimization process targeting to increase the volume of air accessing the combustion space and to increase the turbulence of the air at the end of the compression stage. One of the first conclusions will be that the valve diameter is a fine tradeoff between the need for a bigger diameter involving a greater mass of air filling the cylinder, and the need of a smaller diameter in order to reduce the blind zone. Here there is room for optimization studies. The relative pressure indicates a suction effect coming from the moving piston. The more the shape of the inlet port is smoother and the diameter of the piston is bigger, the aerodynamic resistance of the geometry will be smaller so that the difference of inlet port pressure and the pressure near to piston face will be smaller. Here again there is enough room for more optimization studies.

The interaction of a liquid with the surrounding air produces unstable waves that disintegrate the liquid into droplets, which is known as liquid atomization. The common internal flow of a liquid atomization nozzle experiences a single-phase flow but might turn into a multiphase flow with the existence of cavitation. Cavitation in internal flow has gotten a lot of attention because of the positive and negative consequences it can have depending on the application. One such advantageous result is that cavitation has been used to promote the atomization of liquid jets by causing gas bubbles in the atmosphere to collapse. Most of the past research on cavitation has focused on the exit orifice's constant cross-section area. The current study investigates the effect of throat location and geometry on cavitation characteristics. Filtered water was used as the simulation fluid. The high-speed shadowgraph technique was applied to record the images of the internal flow patterns. The placement of the throat was discovered to have a substantial impact on the status of the cavitation. Cavitation began at the inlet of the throat when the throat was placed at the uppermost part of the exit orifice. However, when the throat is placed in the middle of the exit orifice, the cavitation begins at the end of the throat. Four cavitation regimes were identified, namely developing, mixed, super and sudden expansion cavitation. Furthermore, it was found that the discharge coefficient depends on the cavitation's state and length, except when the cavitation is in the supercavitation regime.

This paper describes our eorts to compute convective heat transfer through gas-turbine blade-cooling passages. The in¯uence on the mean and turbulent ¯ow due to surface rib-roughness is the main focus. A number of turbulence models, of eective viscosity (EVM) and second-moment type, are applied to the computation of ¯ow and heat transfer through ribbed-roughened passages. Computations of ¯ow through a rib-roughened U-bend show that second moment closures are necessary in order to correctly reproduce the regions of ¯ow separation. Heat transfer computations through two-and also three-dimensional ribbed passages reveal that low-Re turbulence models are necessary and that a low-Re dierential stress closure yields thermal predictions that are superior to those of the low-Re EVM model. A dierential version of the Yap length-scale correction term, independent of the wall distance, is introduced to the dissipation rate equation and is found to improve the heat transfer predictions of the low-Re kÀ model.

The advantages of variable power control for heat-balance sap flow gauges are evident under high flow rates (e.g., .600 g h 21 ) where high rates of power must be applied. Under the very high flow rates (e.g., 1500-4000 g h 21 ) of mature grapevines (Vitis spp.), we evaluated two algorithms to control the power applied to heat-balance sap flow gauges, and thus the temperature difference (DT) above and below gauge heaters: (i) a proportional-derivative (PD) algorithm and (ii) an open-loop controller following the theoretical diurnal course of irradiance. The PD algorithm was tuned for expected maximum flow rates and could keep DT within 0.1°C of its daytime (0800-1800 h) target value. Over 21 d, mean daytime DT was 1.32 6 0.001°C (s.e.m.) for an 18-gauge system. The algorithm was unstable early in the morning and in the evening as rates of sap flow were below those for which the algorithm had been tuned. In the open-loop algorithm, power output was programmed to change according to a sine curve tied to daylength. In well-watered vines, the power curve mimicked actual sap flow patterns. As flow rates varied it accommodated the changing dead time of the system, which is the delay or time required before any change in DT occurs. Daytime DT varied sinusoidally with a typical amplitude of 0.5 to 1.0°C. The coefficient of variation in daytime DT appeared to be higher (16-26%) under the open-loop algorithm than under the PD algorithm (5-13%). Under weekly cycles of deficit irrigation, the variance in daytime DT increased with the number of days after irrigation, suggesting that the open-loop algorithm might best be applied when the stem energy balance includes an estimate of heat storage.

Helico-axial pumps are designed to pump mixtures of gas and liquid. Secondary flows and rotor-stator interactions are known to add complexity to the flow field in unshrouded axial-flow turbomachinery. Here we use a high-speed camera to visualize the internal flow field in a multistage helico-axial pump. A wide range of relative flow rates are investigated to see how secondary flows emerge and evolve depending on the operating point. Nitrogen bubbles are used as tracers to obtain a qualitative understanding of the flow. The recordings exhibit a highly unsteady flow field that varies with the relative flow rate. The tip leakage flow and interactions between the components lead to recirculation and reversed flow, also when operating near the best efficiency point. Local gas accumulation and stagnant fluid was observed near the impeller outlet at very low relative flow rate, where the slope of the head-flow curve had shifted.

The computation of flows within interconnected, multiple-disk cavities shows strong interaction between the cavities and the power stream. For this reason, simulations of single cavities in such cases are not realistic; the complete, linked configuration must be considered. Unsteady flow fields affect engine stability and can engender power-stream-driven secondary flows that produce local hot spotting or general cavity beating. Further, a concentric whirling rotor produces a circumferential pressure wave, but a statically eccentric whirling rotor produces a radial wave; both waves affect cavity ingestion and the stability of the entire engine. It is strongly suggested that seals be used to enhance turbojet engine stability. Simple devices, such as swirl brakes, honeycomb inserts, and new seal configurations, should be considered. The cost effectiveness of the NASA Lewis Research Center seals program can be expressed in terms of program goals (e.g., the Integrated High-Pressuref[emperature Engine Technology (llIPTET) cannot be achieved without such a program), cost (savings to $250 million/I-percent decrease in specific fuel consumption), and indirect benefits (reduction of atmospheric NO x and CO 2 and reduction of powerplant downtime).

Mechanical behaviour of powders and grains often displays features of solid-like and liquidlike characteristics of matter. In spite of processing granular materials quite extensively in the industries, their flow behaviour is still complex to understand under different process conditions. In this paper, using Digital Particle Image Velocimetry (DPIV) and high speed videography, we probe systematically on the spatial and temporal distribution of the velocity fields of pharmaceutical excipient granules flowing though smooth hoppers with different internal (orifice) angles. This helps to visualise and identify the locations and formation of the flow channels and conversely the stagnation zones of granular materials inside the hoppers as a function of the internal angle of the hoppers. We show that even when a powder characterised as a free-flowing type in the conventional sense could experience a significant level of hindrance to flow when passing through smooth hoppers of different internal angles and its impact increases with increase in the internal angle. Theoretical predictions are made using experimentally evaluated grain-scale properties as input parameters for understanding the effects of hopper angle on the granular flow rate. A good level of agreement is obtained between the experimental and theoretical estimates of the granular flow rate in terms of the hopper angle. The outcomes presented here are a step forward in designing granular flow devices more efficiently in the future.

The aim of this paper is to present a fractional scaling analysis (FSA) application for a system with interacting components where multiple figures of merits need to be respected during complex transient accident scenario with several consecutive time sequences. This paper presents FSA application to the International Reactor Innovative and Secure (IRIS) reactor and Simulatore Pressurizzato per Esperienze di Sicurezza 3 (SPES3) integral effects test (IET) facility. The FSA was applied for the small break loss of coolant accident (SBLOCA) on the direct vessel injection (DVI) line as the most challenging transient scenario. The FSA methodologies were applied for two figures of merits: (1) reactor and containment vessels pressure responses, and (2) reactor vessel water collapsed level response. The space decomposition was performed first. The reactor vessel and containment vessel were divided in components so that important phenomena and their consequences can be evaluated in each of t...

The SPES3 facility is being built at the SIET laboratories, in the frame of an R&D program on Nuclear Fission, led by ENEA and funded by the Italian Ministry of Economic Development. The facility is based on the IRIS reactor design, an advanced medium size, integral layout, pressurized water reactor, based on the proven technology of PWR with an innovative configuration and safety features suitable to cope with Loss of Coolant Accidents through a dynamic coupling of the primary and containment systems. SPES3 is suitable to test the plant response to postulated Design and Beyond Design Basis Events, providing experimental data for code validation and plant safety analysis. It reproduces the primary, secondary and containment systems of the reactor with 1:100 volume scale, full elevation, prototypical fluid and thermal-hydraulic conditions. A design-calculation feedback process, based on the comparison between IRIS and SPES3 simulations, performed respectively by FER, with GOTHIC and ...

Heat convection from the uniformly heated walls of a straight channel in presence of a rotationally oscillating cylinder (ROC) is simulated at Re ¼ 100. Heat transfer enhancement due to vortex shedding from the ROC is investigated. Systematic studies are performed to explore the rotation angle and frequency influences on heat transfer by varying the latter in range of the lock-in regime and the former from 0 to 2p/3. All simulation results are based on the numerical solutions of two-dimensional, unsteady, incompressible NaviereStokes and energy equations using an h/p type finite element algorithm. Considering time periodicity of the resulting flow and temperature fields, time averaged wall Nusselt number is reported to quantify the heat transfer enhancement for Pr ¼ 0.1, 1.0, 5.0 and 10.0 fluids. Performance analyses of the ROC device based on its total power consumption and heat transfer enhancement are also presented.

The recent developments of the CFD tools enable predicting the fluid dynamic, heat transfer, combustion, chemical reaction and spray formation process even in very complex geometries with a sufficient degree of accuracy and acceptable computational costs by numerical solutions of the governing conservation equations that have become a realizable goal. The principal components of these multidimensional engine flow models contain the mathematical models, the discretization procedures, and the solution algorithm. In addition, mathematical models or equations are used to describe the flow processes. Especially turbulence model, describing the small-scale features of the flow, is essential. The dynamic mesh model in Star-CD can be used to model flows where the shape of the domain changes with time due to motion on the domain boundaries. The update of the volume mesh is handled automatically by Star-CD at each time step based on the new positions of the boundaries. To use the dynamic mesh model, you need to provide a starting volume mesh and describe the motion as valve profile of any moving zones in the model. A simplified 3D geometry (from Imperial College compressing engine) will be used for this work, consisting of a simple compressor geometry, the bottom wall representing the piston. The simulation will be performed in an axisymmetric geometry from the TDC position (i.e., CA =0 0) to the end of the compression stroke (i.e., CA=3600). The development of CFD methodology for IC engine design represents a particular challenge due to the complex physics and mechanics. Turbulence modeling is one of the critical parameters for ICE CFD applications. Standard k- model has been widely used for the CFD calculation for the IC engine applications, other turbulence models are used as k-- model (Gul extended a three-equation model) that can have a better account for compression and expansion effects. The main task of this project is to provide a numerical simulation of the intake flow field

This paper deals with an investigation of the phenomenon of Helmholtz resonance under oblique wind flow, and an examination of the applicability of the quasi-steady approach to internal pressures in buildings with a dominant opening. Studies on a 1:50 scale model of the Texas Tech University (TTU) test building in a boundary layer simulation show that 'Helmholtz resonance under oblique wind flow' produces an extremely strong response in internal pressure fluctuations, in comparison with that obtained under normal onset flow. It is verified that 'eddy dynamics over the opening' rather than 'freestream turbulence' is responsible for the intense excitation at oblique flow angles, implying that even if the Helmholtz resonance frequency were to be in the tail of the freestream turbulence spectrum, severe excitation would still be possible.Experimental measurements of internal pressures for a range of opening situations also reveal that the quasi-steady approach is inapplicable in the prediction of peak internal pressures. Furthermore, it is demonstrated that while the provisions of the Australian/New Zealand wind loading code-AS/NZS1170.2:2002, which is based upon the quasi-steady method, is adequate as far as mean internal pressures are concerned, it however underpredicts peak internal pressures in some situations. In particular, for the range of situations studied, measurements indicated that peak pressures were up to 25% higher than the AS/NZS1170.2:2002 provisions, in the case of openings in the positive pressure and sidewall regions. It is also shown that for openings located in the sidewall region, peak internal pressures could be just as extremely positive as it can be negative. It is suggested that in the calculation of internal pressures, the AS/NZS1170.2:2002 provide for the use of local pressure factors K l ; that are at present applied only to external pressure calculations. Secondly, the code should provide for internal pressure coefficients to be both negative and positive, when openings are located in sidewall regions. Finally, in order to account for the

Gasoline Direct Injection (GDI) systems have become a rapidly developing technology taking up a considerableand rapidly growing share in the Gasoline Engine market due to the thermodynamic advantages of direct injection. The process of spray formation and propagation from a fuel injector is very crucial in optimizing the air-fuel mixture of DI engines. Previous studies have shown that the presence of some cavitation in high-pressure fuel nozzles can lead to better atomization of the fluid. However, under some very specific circumstances, high levels of cavitation can also delay the atomization process; spray stabilization due to hydraulic flip is the most well-known example. Therefore, a better understanding of cavitation behavior is of vital importance for further optimization of next generation fuel injectors.In contrast to the abundance of investigations conducted on the inner flow and cavitation patterns of diesel injectors, corresponding in-depth research on the inner flow of g...

Submitted for the DFD19 Meeting of The American Physical Society Numerical investigation of the flow in gas turbine blade trailing edge internal cooling passages JAEHYUN RYU, WONTAE HWANG, Seoul National University-Gas turbine blades operate at very high temperatures, often beyond material limits. Internal and external cooling enable the blade to survive these extreme temperatures. The trailing edge of the blade is designed to be sharp for high aerodynamic efficiency, but this makes internal convective cooling poor at the corner. The effect of ribs was assessed in a right triangle channel containing a sharp corner, representing a simplified trailing edge. First, 45 angled ribs on the pressure and suction side walls were investigated. The Reynolds-averaged Navier-Stokes (RANS) results show fairly good agreement with previous results from magnetic resonance velocimetry (MRV) and large eddy simulation (LES). Different turbulence models were assessed, and the baseline explicit algebraic Reynolds stress model (BSL EARSM) was adequate in capturing the flow structure. Next, we optimized rib geometry via design of experiments (DOE), by changing the rib height to channel height ratio and rib angle. 3-level full factorial design (FFD) was used to determine the DOE points. Streamwise flow velocity at the sharp corner and friction factor were set as objective functions. The corner flow velocity increases as the rib is angled less toward the flow, at the penalty of an increase in friction factor.

The potentials of microstructured systems have already been demonstrated for a large number of applications in chemical engineering. Nevertheless, the rational use of these systems at industrial scale rises new questions, among which the strategies to structure internal flow appear as a key issue. The present study explores the geometries of complex flow networks with parallelized channels and highlights their respective design issues. The impact of arranging channels of different dimensions on the thermal performances of the resulting multi-scale networks is investigated considering the flow maldistribution problem. The hydrothermal network efficiencies are quantified and compared with respect to several geometrical and physical constraints, in order to propose design guidelines and channel arrangement strategies.

In this work, a collaborative experimental study has been conducted to assess the effect an imposed internal pressure has on the controlling the hydrodynamic performance of a compliant composite hydrofoil. It was expected that the internal pressure together with composite structures be suitable to control the hydrodynamic forces as well as cavitation inception and development. A new concept of morphing hydrofoil was developed and tested in the cavitation tunnel at the French Naval Academy Research Institute. The experiments were based on the measurements of hydrodynamic forces and hydrofoil deformations under various conditions of internal pressure. The effect on cavitation inception was studied too. In parallel to this experiment, a 2D numerical tool was developed in order to assist the design of the compliant hydrofoil shape. Numerically, the fluid-structure coupling is based on an iterative method under a small perturbation hypothesis. The flow model is based on a panel method an...

This paper examines the steady-state three dimensional momentum and internal energy change in rotating viscoelastic fluid flow along with convective boundary conditions. In most of the literature, the thermophysical properties of the fluid are assumed to be constant. But current analysis fills this gap by taking viscosity, conductivity and diffusivity to be temperature dependent. In order to create a chemical reaction in a system activation energy is added. Velocity of the fluid over an exponential three dimensional surface is varied exponentially while a Casson fluid model is assumed for temperature dependent viscosity. A similarity transformation diminishes the Navier-Stokes partial differential equations into ordinary differential equations and then solved numerically using Bvp4c for the velocity, temperature and concentration distributions. Moreover, drag forces, heat and mass transfer rates near the surface are calculated numerically in tabular form. Outcomes are discussed for parameters appearing in dimensionless system like rotating parameter, the viscoelastic parameter, Eckert number, Prandtl number, temperature distinction parameter, Schmidt number, thermal and concentration Biot numbers and variable viscosity, conductivity and diffusivity parameters. We found that the minimum force required to initiate the fluid motion increases with an increment in local rotation parameter O. An accretion in O exhibits curiously oscillatory pattern in velocity profile. Casson fluid b and viscosity parameter h r has adverse influence on temperature profile. The fitted rate n and temperature difference parameter d have conflicting influence on concentration profile. Activation energy E and Eckert number Ec causes increment in the behavior of temperature profile. In addition, numerical data of previous papers are matched with current data.

This paper describes the results of CFD prediction of performance, internal flow fields and thrust force acting on the impellers of a three-stage centrifugal pump which was provided for the Workshop "Single-&Multistage Pump Flow Prediction". URANS (Unsteady Reynolds Averaged Navier-Stokes) was applied for the CFD prediction. Parts of the results were already reported by the authors. In this paper, more details are described, especially on the relationship between the changes of the flow fields in the pump and performance of axial thrust characteristics. The effects of axial shift on the performance and axial thrust characteristic are also investigated. URANS calculations were conducted at the design flow (Qd) to a near shut-off condition (10% Qd). The predicted Q-H performance shows a good agreement with the experiments. This pump shows positive slope in the head curve near the shut-off condition. URANS predicted the positive slope in the head curve near the shut-off condition, its flow rate, however, was slightly higher than that of the experiment. The reverse flow between the impeller and the diffuser developed when the flow rate was reduced. The interaction between the reverse flows and the flow in the side-wall gaps (front, back) affects pressure distributions and then axial thrust acts on the impeller. The details of the change of the interaction by flow rate predicted by URANS are described including the effects of axial shift of the rotor. URANS predicted earlier change in the axial thrust characterized by axial shift of the rotor than occurred in the experiments. This discrepancy was caused by interaction between reverse flows and side wall gap flows starting at higher flow than in the experiments.

This paper describes the results of CFD prediction of performance, internal flow fields and thrust force acting on the impellers of a three-stage centrifugal pump which was provided for the Workshop "Single-&Multistage Pump Flow Prediction". URANS (Unsteady Reynolds Averaged Navier-Stokes) was applied for the CFD prediction. Parts of the results were already reported by the authors. In this paper, more details are described, especially on the relationship between the changes of the flow fields in the pump and performance of axial thrust characteristics. The effects of axial shift on the performance and axial thrust characteristic are also investigated. URANS calculations were conducted at the design flow (Qd) to a near shut-off condition (10% Qd). The predicted Q-H performance shows a good agreement with the experiments. This pump shows positive slope in the head curve near the shut-off condition. URANS predicted the positive slope in the head curve near the shut-off condition, its flow rate, however, was slightly higher than that of the experiment. The reverse flow between the impeller and the diffuser developed when the flow rate was reduced. The interaction between the reverse flows and the flow in the side-wall gaps (front, back) affects pressure distributions and then axial thrust acts on the impeller. The details of the change of the interaction by flow rate predicted by URANS are described including the effects of axial shift of the rotor. URANS predicted earlier change in the axial thrust characterized by axial shift of the rotor than occurred in the experiments. This discrepancy was caused by interaction between reverse flows and side wall gap flows starting at higher flow than in the experiments.

Concentrated solar power technologies have been studied in recent years as a potential solution for energy production industry , however this kind of systems face different challenges in order to increase thermal performance and efficiency. This paper presents the results of a thermal analysis on a parabolic trough collector with different receivers internal fins configurations, systems were studied in CFD Solidworks® flow simulation software and compared with a traditional parabolic collector with cylindrical receiver. Results shows that the lowest thermal performance was achieved with a cylindrical pipe, instead fractal fins receiver with 5 internal fins achieves a temperature increase of 27% and the best pipe configuration was fractal Descartes with 12 internal pipes which e the cylindrical temperature in 29%.

An Italian MSE R&D programme on Nuclear Fission is funding, through ENEA, the design and testing of SPES3 facility at SIET, for IRIS reactor simulation. IRIS is a modular, medium size, advanced, integral PWR, developed by an international consortium of utilities, industries, research centres and universities. SPES3 simulates the primary, secondary and containment systems of IRIS, with 1:100 volume scale, full elevation and prototypical thermal-hydraulic conditions. The RELAP5 code was extensively used in support to the design of the facility to identify criticalities and weak points in the reactor simulation. FER, at Zagreb University, performed the IRIS reactor analyses with the RELAP5 and GOTHIC coupled codes. The comparison between IRIS and SPES3 simulation results led to a simulation-design feedback process with step-by-step modifications of the facility design, up to the final configuration. For this, a series of sensitivity cases was run to investigate specific aspects affecti...

The aim of this paper is to present a fractional scaling analysis (FSA) application for a system with interacting components where multiple figures of merits need to be respected during complex transient accident scenario with several consecutive time sequences. This paper presents FSA application to the International Reactor Innovative and Secure (IRIS) reactor and Simulatore Pressurizzato per Esperienze di Sicurezza 3 (SPES3) integral effects test (IET) facility. The FSA was applied for the small break loss of coolant accident (SBLOCA) on the direct vessel injection (DVI) line as the most challenging transient scenario. The FSA methodologies were applied for two figures of merits: (1) reactor and containment vessels pressure responses, and (2) reactor vessel water collapsed level response. The space decomposition was performed first. The reactor vessel and containment vessel were divided in components so that important phenomena and their consequences can be evaluated in each of t...

A marching in time finite-volume numerical procedure is presented for three-dimentional Euler analysis of internal configuration flows using general curvilinear coordinates. The results of the performed experiments could be used not only to back up the predictions of the proposed numerical technique, but at the same time to shed more light on the threedimensional transonic and supersonic internal flow behaviour. Numerical solution results have been presented and compared with measurements as well as with predictions using two other three-dimensional flow solvers. 1Introduction The non working flow passages constitute transitional pieces with sharp bends, rapid flow area changes and irregular cross sections. Nowdays, 3D Euler solvers are well developed and are available for routine turbomachinery calculations. Several of these dealing with internal and external flows are described by Hirsch*. Stuart and Hetherington as early as in 1974 determined the solution for the full 3D inviscid...

In this paper, we presented the computed results for the effects of an externally applied homogeneous magnetic field on the development of internal flow separation in a two-dimensional symmetrical channel with walls parallel upstream but not parallel elsewhere. The particular example studied most fully is that of gradual exponentially diverging channel. The solution for the flow governing non-linear equation is found using perturbation method together with Padé approximation technique. Our results reveal that internal flow separation development at moderately large Reynolds number is suppressed by an increase in magnetic field intensity.

A simplified approach to simulate turbulent flows in curved channels is proposed. A set of governing equations of motion in Cartesian coordinates is derived from the full Navier-Stokes equations in cylindrical coordinates. Terms to first order in the dimensionless curvature parameter are retained, whereas higherorder terms are neglected. The curvature terms are implemented in a conventional Navier-Stokes code using Cartesian coordinates. Direct numerical simulations (DNS) of turbulent flow in weakly curved channels are performed. The pronounced asymmetries in the mean flow and the turbulence statistics observed in earlier DNS studies are faithfully reproduced by the present simplified Navier-Stokes model. It is particularly rewarding that also distinct pairs of counter-rotating streamwise-oriented vortices are embedded in the simulated flow field.

A simplified approach to simulate turbulent flows in curved channels is proposed. A set of governing equations of motion in Cartesian coordinates is derived from the full Navier-Stokes equations in cylindrical coordinates. Terms to first order in the dimensionless curvature parameter are retained, whereas higherorder terms are neglected. The curvature terms are implemented in a conventional Navier-Stokes code using Cartesian coordinates. Direct numerical simulations (DNS) of turbulent flow in weakly curved channels are performed. The pronounced asymmetries in the mean flow and the turbulence statistics observed in earlier DNS studies are faithfully reproduced by the present simplified Navier-Stokes model. It is particularly rewarding that also distinct pairs of counter-rotating streamwise-oriented vortices are embedded in the simulated flow field.

In this paper the description of the internal flow in a Francis turbine is addressed from a numerical point of view. The simulation methodology depends on the objectives. On the one hand, steady simulations are able to provide the hill chart of the turbine and energetic losses in its components. On the other hand, unsteady simulations are required to investigate the fluctuating pressure dynamics and the rotor-stator interaction. Both strategies are applied in this paper to a working Francis turbine in Colombia. The employed CFD package is ANSYS-CFX v. 11. The obtained results are in good agreement with the in site experiments, especially for the characteristic curve.

The alternating movement of the inlet valve and the piston of an internal combustion engine generates pressure waves propagating along the intake duct. This phenomenon alters the admitted air mass flow inside the engine cylinder in some speed ranges. To mitigate the harmful effects of the wave phenomenon, acoustic elements are inserted into the intake system, such as Helmholtz resonators, plenums and Herschel-Quincke tubes. This paper aims to numerically evaluate the air flow in the intake ducts using Herschel-Quincke tubes. The numerical study was carried out using software based on the Characteristics Method, which, considering the one-dimensional transient flow, simulates the wave phenomena inside the ducts. As a result, it was observed that the Herschel-Quincke tubes reduce the pressure amplitude at the inlet valve port, increasing the air flow velocity and the intake air mass flow.

In the presented paper authors focused on numerical analysis of the flow through selected constructions of Kaplan and semi-Kaplan machines. The paper contains three computation examples; each of them concentrates on different aspects of computational fluid dynamics (CFD) utilization. The numerical tests of various turbulent models for Kaplan turbine CFD applications, numerical determination of the cam curve characteristic and numerical analysis of operating parameters of the semi-Kaplan machine have been presented. The methodology of the implemented numerical computations and final results of calculations have been discussed in each of the presented study cases.

Three-node triangular elements obtained from the intersecting diagonals of quadrilaterals are thoroughly investigated for the penalty method formulation of incompressible problems such as Stokes flow, Navier-Stokes flow, and small-deformation rubber elasticity. Equivalence of the present formulation to the one using Cnode quadrilateral isoparametric elements with selective reduced integration, is presented. Convergence, instability phenomenon, smoothing of the pressure distribution are studied together with decompositions into triangular elements.

In Chile, commercial avocado production has expanded to areas with poorlydrained soils that are low in oxygen. In these soils, improper irrigation design or management can limit fruit production and quality due to flooding of the root zone. The effects of soil flooding on stomatal conductance, transpiration, leaf chlorophyll content (estimated with a SPAD meter) and vegetative growth of one-year-old 'Hass' avocado trees (Persea americana Mill.) grafted onto one of three different seedling rootstocks were studied in a greenhouse. Trees grafted onto Mexicola, Zutano or Nabal rootstock were subjected to one of two flooding treatments: 1) non-flooded (control) or 2) flooded for six days. After the flooding period, flooded plants were removed from the flood water, placed in the same conditions as the control plants and their responses were measured during a six-day recovery period. Visible symptoms of flooding were desiccation of the shoot apex and leaf abscission. There were no consistent differences between rootstocks for stomatal conductance or transpiration during the flooding period. However, during the recovery period, trees on Mexicola rootstock had higher stomatal conductance and transpiration and appeared more vigorous than trees on the other rootstocks. Root, leaf and total plant dry weights and leaf chlorophyll content were significantly lower for flooded than nonflooded trees. The data indicated that 'Hass' avocado grafted onto Mexicola rootstock are able to recover from six days of soil flooding better than trees grafted onto Zutano or Nabal rootstocks.