Active Control of Fluid Flows

The design of high lift systems for commercial aircraft has a substantial potential to contribute to the achievements of the challenging goals formulated in the European Vision for 2020. Basically, efficient innovative high lift devices are the pre-requisite for improvements in two fields: the first is the reduction of the perceived aircraft noise, as the airframe, more precisely the slat, has become the main source of noise during the landing phase. The second field is the strong reduction of CO 2 emissions. Whatever advanced aerodynamic concept is considered, the objective is to achieve a reduced perceived noise level for the airport and its residents while sustaining or improving the high lift performance itself, e.g. by means of flow control. High fidelity numerical methods together with a detailed understanding of the high lift flow physics and scaling effects are key issues to accomplish the envisaged improvements.

Tablo 6.14: Bölüm 4'te önerilen yöntem ve Zhang (1991) yönteminin karmatip ARMA(2,2,2,2) modeli için ürettiği MA parametre kestirimleri……………...…………………..………………….... 98 Tablo 6.15: Tablo 6.13 ve Tablo 6.14 'de verilen istatistiklerin başarım ölçütlerine göre değerlendirmesi……………………………......... 99 viii ŞEKİL LİSTESİ Sayfa No Şekil 1.1: Parametrik modelden rastgele süreç üretimini sağlayan yapının blok diyagramı…………………………………………………… Şekil 1.2: Gözlem verisinin doğrudan doğruya ARMA model parametreleri ile temsiline yönelik literatürdeki çalışmalarda izlenen adımların blok diyagramı.……………………………………….………….. Şekil 1.3: Gözlem verisinin ARMA izge parametreleri ile temsiline yönelik literatürdeki çalışmalarda izlenen adımların blok diyagramı.

Large-eddy simulations and full-scale investigations were carried out that aimed to reduce the aerodynamic drag and thus the fuel consumption of trucktrailers. The computational model is a relevant generic truck-trailer combination, and the full-scale is a corresponding Volvo prototype vehicle. Passive and active flow control (AFC) approaches were adopted in this work and applied at the rear end of the trailer. Flaps were mounted at an angle that induces separation, and synthetic jet actuators were placed close to the corner of the rear end and the flaps. The drag reduction obtained is in the order of 30%. The flow was analyzed by comparing the phase-averaged and time-averaged flow field of the unforced and the forced cases. The full-scale prototype is a Volvo truck-trailer. The trailer is mounted by three flaps at the rear sides and top end. The actuators consist of loudspeakers in sealed cavities, connected to amplifiers that are supplied with a frequency generator controlled by LabVIEW. The full-scale test includes passive and active flow control investigations by varying the flap angle, with and without AFC, investigating different frequency and slot angle configurations. The fuel flux was measured during the full-scale test. The test shows a fuel reduction of about 4% in a comparison of two flap angles. The test of active flow control shows a reduction of 5.3% compared to the corresponding unforced case. Compared with the baseline case, the passive flow control fails to reduce the total fuel consumption.

Active flow control is probably the most challenging research area in vehicle aerodynamics. Being able to manipulate a flow field in order to achieve desired results beneficial to engineering is the only way to meet today's demands for competitive and efficient solutions in the automotive industry. The current work studies the flow control on a semi detailed model truck by using detached-eddy simulations and wind tunnel experiments aiming at reducing the aerodynamic drag. This study combines both passive and active flow control applied on the rear end of the trailer. An indigenous fluidic actuator (loudspeaker in cavity with slots) is used as a synthetic jet in the experiment. Both experiments and computations demonstrate that the active flow control works successfully and results in flow reattachment to the flaps. The numerical simulations show that the drag coefficient, ‫ܥ‬ ‫ܦ‬ , decreased by 3.9% when AFC was activated compared to the baseline case without flaps. The corresponding decrease when AFC was deactivated (with flaps) was only 0.7%. The experimental results show a decrease of ‫ܥ‬ ‫ܦ‬ by 3.1% for the case with activated AFC compared to the baseline case. When AFC was deactivated the corresponding decrease in ‫ܥ‬ ‫ܦ‬ was 1.8%. A detailed flow analysis made in computations and experiments is used to explain these results.

Heading control of an Unmanned Aerial Vehicle, UAV is a vital operation of an autopilot system. It is executed by employing a design of control algorithms that control its direction and navigation. Most commonly available autopilots exploit Proportional-Integral-Derivative (PID) based heading controllers. In this paper we propose an online adaptive reinforcement learning heading controller. The autopilot heading controller will be designed in Matlab/Simulink for controlling a UAV in X-Plane test platform. Through this platform, the performance of the controller is shown using real time simulations. The performance of this controller is compared to that of a PID controller. The results show that the proposed method performs better than a well tuned PID controller.

L'objectif final de cette étude est d'utiliser un mod`ele réduit construit par POD pour contrôler un écoulement de cavité ouverte en régime compressible. Dans cette communication, nous utiliserons des méthodes de calibration pour améliorer la précision du mod`ele réduit et nous nous ...

Two control input separation methods for controloriented reduced-order modeling of flow systems are developed and implemented in a cavity flow experimental facility. The proposed methods are 1) actuated POD expansion with stochastic estimation and 2) optimization on a Hilbert space, respectively. These methods extend the baseline flow model through the use of innovation vectors, which capture the distance of the actuated flow from the baseline space. This technique remedies certain gaps associated with the sub-domain separation method employed in our earlier works by 1) producing models that exactly reduce to baseline case under no input, 2) not requiring an identifiable control region and 3) improving the estimation of the control terms. The methods are evaluated in experiments to test their ability to achieve reconstruction of the flow. Also, the performance of closed loop controllers built from models based on these new techniques are analyzed. It is seen that these controllers perform satisfactorily in terms of resonance peak suppression, and compare favorably over the old one in terms of power consumption.

An aircraft’s aerodynamic efficiency largely depends on lift and drag forces, stall angle at different stages of flight. The increase of lift and stall angle improve maneuverability and performance of any fixed wing aircraft. An experimental investigation has been conducted on a two dimensional NACA 2415 airfoil equipped with a rotating cylinder at leading edge. Rotating cylinder serve as active control device for boundary layer flow separation, thus increasing airfoil’s lift and stall angle of attack. The effect of angle of attack, momentum injection ratio (ratio of cylinder linear motion to free stream air velocity) on the lift coefficient, drag coefficient and stall angle of attack are investigated in this study. The use of rotating cylinder at the leading edge of the airfoil increases the lift coefficient compared to the conventional NACA 2415 airfoil about 38.63% and stall angle increases to 16° from 12° at momentum injection ratio of 0.1173.

Öz: Bu çalışmada ekli (additive) Allee etkisine sahip Caputo-Fabrizio lojistik model ele alınmıştır. Adams-Bashfort nümerik yöntemiyle kesirsel mertebeden dinamik sistemden iki boyutlu bir fark denklem sistemi elde edilmiştir. Bu fark denklem sisteminin denge noktaları hesaplanmış ve her bir denge noktasının lokal asimptotik kararlılığı için gerekli olan cebirsel koşullar Schur-Cohn kriterlerinin kullanılmasıyla elde edilmiştir. Ayrıca fark denklem sisteminin, pozitif denge noktası civarında Neimark-Sacker çatallanması sergilediği gösterilmiştir. Yine Allee fonksiyonunun sistemin dinamik yapısı üzerindeki etkisi araştırılmıştır. Allee fonksiyonunun kararlılık bölgesini genişlettiği ve daha geç çatallanmaların oluşmasına sebebiyet verdiği gözlemlenmiştir. Son olarak bütün teorik sonuçlar nümerik olarak test edilmiştir.

The article discusses the issues of the critical infrastructure security management from the perspective of entities responsible for its security and development of an integral model of critical infrastructure security, and shows the methodology of situational management of critical infrastructure safety. Proposed solutions are used for CI mapping, enabling the generation of adverse event scenarios, estimation of the risks dependent on the considered CI, and determination of decision problem, indicating a set of protection activities for elimination or reduction of the risk in the security threshold.

High Power Synthetic Jet Actuator (SJA) based on compact piezoelectric actuators, have been developed and tested by CEDRAT TECHNOLOGIES (CTEC) and ONERA, under French National funding RAPID from DGA. This publication presents the modelling approach with early breadboarding results, the final design chosen for integration onto an aircraft airfoil mock-up, the performance test results on the SJA device prior integration, and the final aerodynamic performance test demonstration achieved at ONERA wind tunnel test facility.

This paper describes the structural design of an active flow-control experiment. The aim of the experiment is to investigate the increase in efficiency of an internally blown Coanda flap using unsteady blowing. The system uses tailor-made microelectromechanical (MEMS) pressure sensors to determine the state of the oncoming flow and an actuated lip to regulate the mass flow and velocity of a stream near a wall over the internally blown flap. Sensors and actuators are integrated into a highly loaded system that is extremely compact. The sensors are connected to a bus system that feeds the data into a real-time control system. The piezoelectric actuators using the d 33 effect at a comparable low voltage of 120 V are integrated into a lip that controls the blowout slot height. The system is designed for closed-loop control that efficiently avoids flow separation on the Coanda flap. The setup is designed for water-tunnel experiments in order to reduce the free-stream velocity and the system's control frequency by a factor of 10 compared with that in air. This paper outlines the function and verification of the system's main components and their development.

Modeling and simulation is one of the common and reliable methods that are used before product development and validation & verification processes to solve aerospace problems for many years. In the recent years, model-driven development techniques became very popular and widespread among aerospace researchers. However, traditional model-driven simulation development approaches can be insufficient for multi-agent simulations. Lack of maintainability, reusability, and ability to run large number of simulations in acceptable time periods are some of those insufficiencies. To overcome these problems, one of the suggestions is promoting object-oriented programming and agent-based modeling and simulation approaches in aerospace. However, these approaches are not well-known and widely used among aerospace researchers. Therefore, creating models by using these approaches are really complicated and unusual from the viewpoint of developers. As a result, modeling with these approaches is not w...

An aircraft’s aerodynamic efficiency largely depends on lift and drag forces, stall angle at different stages of flight. The increase of lift and stall angle improve maneuverability and performance of any fixed wing aircraft. An experimental investigation has been conducted on a two dimensional NACA 2415 airfoil equipped with a rotating cylinder at leading edge. Rotating cylinder serve as active control device for boundary layer flow separation, thus increasing airfoil’s lift and stall angle of attack. The effect of angle of attack, momentum injection ratio (ratio of cylinder linear motion to free stream air velocity) on the lift coefficient, drag coefficient and stall angle of attack are investigated in this study. The use of rotating cylinder at the leading edge of the airfoil increases the lift coefficient compared to the conventional NACA 2415 airfoil about 38.63% and stall angle increases to 16° from 12° at momentum injection ratio of 0.1173.

An aircraft’s aerodynamic efficiency largely depends on lift and drag forces, stall angle at different stages of flight. The increase of lift and stall angle improve maneuverability and performance of any fixed wing aircraft. An experimental investigation has been conducted on a two dimensional NACA 2415 airfoil equipped with a rotating cylinder at leading edge. Rotating cylinder serve as active control device for boundary layer flow separation, thus increasing airfoil’s lift and stall angle of attack. The effect of angle of attack, momentum injection ratio (ratio of cylinder linear motion to free stream air velocity) on the lift coefficient, drag coefficient and stall angle of attack are investigated in this study. The use of rotating cylinder at the leading edge of the airfoil increases the lift coefficient compared to the conventional NACA 2415 airfoil about 38.63% and stall angle increases to 16° from 12° at momentum injection ratio of 0.1173.

Dimensions and material specifications of a commercial rotameter were used for investigating steady and transient flow structure in a rotameter with a ball float. Since drag coefficient of sphere versus Reynolds number is well known and the range of the commercial rotameter is given, the investigation relies on strong validation data. An axially symmetric geometric model is used for steady analysis of the system as the initial step of the investigation. Assessing the proper mesh structure and turbulence model is aimed for this step. Then full three dimensional solid model is put into transient analysis with RANS and LES models. Vortex shedding frequency, Strouhal number and drag coefficient values are evaluated. Vortex induced vibrations are assessed according to transient results. The work is a preliminary study for future investigation on rotameter floats. The framework of future studies is also presented.

In the present study, the wake flow field of a submarine model was investigated experimentally in a wind tunnel. The experiments were conducted to determine the effect of the location of control surfaces on the wake inflow to the impeller of the submarine. In order to investigate the effect of the location of control surfaces as the most important innovation of the present study, the aforementioned surfaces were installed in three longitudinal positions ⁄ = 0.89, 0.92, 0.95 on the heel of the submarine model, and the wake flow was measured at the position ⁄ = 0.978 and the Reynolds number 6 × 10 5 by a five-hole probe and a hotwire anemometer. Finally, the longitudinal position ⁄ = 0.95 was selected as the optimal location for the stern planes to improve the wake inflow to the impeller in terms of reducing its total area and the least amount of turbulence and non-uniformity. The results obtained during this study showed that arriving of the holder base's wake to the stern area increases the area and average velocity and subsequently reducing the non-uniformity of the wake flow.

In this paper obtaining local dynamical models for flow control problems using wavelet transform is studied. First, the snapshots of the flow are obtained from computational fluid dynamics (CFD) simulations of the flow. Then wavelet coefficients are obtained using wavelet transform, thresholding and reconstruction. It is seen that it is possible to obtain a satisfactory representation of the flow using only the approximation coefficients. Next, subspace system identification methods are used to obtain a linear dynamical system model representing the time variation of the approximation coefficients. This procedure is repeated for different viscosity values for the fluid, resulting at multiple models at multiple operating points. These models are then represented by a single uncertain model around a nominal model, where the uncertainty is of multiplicative type, and robust control design using D-K iteration is carried out. The method proposed is applied with successful results to a fl...

Bu makalede çırpan kanat çevresindeki değişken akışın dinamik modellemesi için kullanılan yeni bir yöntem göz önüne alınmıştır. Bu yöntemde, öncelikle Parçacık Görüntülemeli Hız Ölçüm Tekniği (PIV) kullanılarak anlık hız görüntüleri elde edilir. Daha sonra görüntü işleme kullanılarak anlık görüntülere kanat profili yerleştirilir. Bu işlenmiş anlık görüntülere Uygun Dikgen Ayrışımı (POD) yöntemi uygulanarak POD modları ve zaman katsayıları bulunur. Son olarak alt-uzay sistem tanılama (ST) yöntemi kullanılarak, daha önce bulunan zaman katsayılarının izdüşümleri kullanılarak ayrık zamanlı durum uzayı dinamik modellemesi yapılır. NACA0012 kanadından alınan veriler için MATLAB kullanılarak önerilen yöntem denenmiştir ve görülmüştür ki, elde edilen dinamik model, akışın davranışını kabul edilebilir bir doğrulukla göstermektedir.

In this paper, nonlinear control systems whose dynamics are quadratic with respect to state, and bilinear with respect to state and input, which exhibit an oscillation caused by a stable limit cycle for zero input are studied. The effect of linear control on this model is analyzed using modal forms and center manifold theory. It is found that the oscillation amplitude depends both on terms linear in the control and those that depend on the center manifold. To exploit the latter, a nonlinear control law is proposed. The closed loop system is simplified using a time varying periodic change of coordinates, time scaling, and averaging. Using center manifold theory, conditions governing the number and stability type of the limit cycles, and analytical expressions for the oscillation amplitude are derived. The results are verified using a finite dimensional cavity flow model as an example.

First-principle-based models of the dynamics of flow systems are often of limited use for model-based control design, not only because of their nonlinear and infinite-dimensional nature, but also because the control input is generally specified as a boundary condition. Proper orthogonal decomposition and Galerkin projection are among the most effective and commonly used methods to obtain reduced-order models of flow dynamics. However, the final form of these models may not account for the presence of a forcing or control input. From a control design perspective, it is desirable to obtain a reduced-order model in which the control input appears explicitly in the dynamic equations. In this paper, two methods for control input separation are introduced and comparatively evaluated in experimentally based reduced-order modeling of cavity flow, both in their ability to reconstruct the forced flowfield and to provide models suitable for feedback control design. The proposed methods, namely, 1) actuated proper orthogonal decomposition expansion and 2) L 2 optimization, extend the baseline flow model through the use of innovation vectors, which capture the deviation of the actuated flow from the baseline space. The new methods address some of the issues associated with the subdomain separation technique employed in our previous works. Linear-quadratic regulator controllers, built using models obtained from the new methods, have been tested on a cavity flow experiment. Although the new models perform satisfactorily and comparably to our previous models in terms of suppression of cavity tones, they offer a substantial advantage in terms of the required input power to achieve a similar or better performance.

The present research describes the numerical investigation of the aerodynamics around a wind turbine blade with a winglet using Computational Fluid Dynamics, CFD. In this project our goal is to applying spiroid winglet to examine of the vortex effects on the tip of wind turbine’s blade known as “NREL offshore 5-MW baseline wind turbine”. At present this method has not yet been implemented in the wind energy sector, in particular because their production still involves excessive costs, compared to the benefits obtainable in terms of wind energy field. A spiroid winglet was investigated with different twist distribution and camber in which pointing towards the suction side (downstream). The comparisons have been done between two operating conditions in terms of pressure, thrust, torque, relative velocity, streamlines, vorticity and then mechanical power.

This paper briefly describes a novel ducted fan inlet flow-conditioning concept that will significantly improve the performance and controllability of ducted fans operating at high angle of attack. High angle of attack operation of ducted fans is very common in VTOL (vertical take-off and landing) UAV systems. The new concept that will significantly reduce the inlet lip separation related performance penalties in the edgewise/forward flight zone is named DOUBLE-DUCTED FAN (DDF). The current concept uses a secondary stationary duct system to control inlet lip separation related momentum deficit at the inlet of the fan rotor occurring at elevated edgewise flight velocities. The DDF is self-adjusting in a wide edgewise flight velocity range and its corrective aerodynamic effect becomes more pronounced with increasing flight velocity due to its inherent design properties. In this manuscript, after a comprehensive discussion of VTOL inlet flow distortion issues, a conventional baseline d...

Leaks arising from aircraft fuel tanks have constantly represented a problem for aircraft manufacturers, operators and maintenance crews. The integral fuel tanks within aircraft structures are in general located within the wings and they rely on sealant materials to prevent leakage through joints and fasteners. However, aircraft integral fuel tanks are designed from a structural point of view first and as a fuel tank second. There are numerous potential leak paths for the fuel on these complex wing structures. The overall aim of the current research was to reduce the fuel leaks in the aircraft fuel tanks at the delivery. Following this approach a company background analysis was performed in order to find out the regions in the fuel tanks susceptible of fuel leaks. A Finite Element Analysis (FEA) of a critical structural member was done to investigate the structural behavior and propose structural improvements. A workcard with instructions to perform a Nondestructive Inspection (NDI)...

Modeling and simulation is one of the common and reliable methods that are used before product development and validation & verification processes to solve aerospace problems for many years. In the recent years, model-driven development techniques became very popular and widespread among aerospace researchers. However, traditional model-driven simulation development approaches can be insufficient for multi-agent simulations. Lack of maintainability, reusability, and ability to run large number of simulations in acceptable time periods are some of those insufficiencies. To overcome these problems, one of the suggestions is promoting object-oriented programming and agent-based modeling and simulation approaches in aerospace. However, these approaches are not well-known and widely used among aerospace researchers. Therefore, creating models by using these approaches are really complicated and unusual from the viewpoint of developers. As a result, modeling with these approaches is not w...

We investigated a non-steady compressor stator flow of the type that would be expected in a pulsed detonation engine. The effects on the stator vane of the last stator stage were discussed and results from the two-dimensional compressor stator cascade in Berlin are presented. Static pressure measurements showed periodic flow separation phenomena on the measurement blade with respect to the working-phase of a choking-device mounted in the wake of the cascade imposing the non-steady outflow condition. By means of active flow control (AFC) it was possible to avoid flow separation on the measurement blade. Furthermore a figure of merit was defined in order to rate the increase of static pressure recovery with respect to the AFC input. Using an optimized AFC setup the flow-field could be stabilized. 1 Introduction When applying pressure gaining combustion concepts to aero-engines or gas-turbines the impact on neighbouring machine parts needs to be taken into account. The constant volume combustion (CVC) is a promising concept in order to improve the overall efficiency of a gas turbine. Stathopoulos et al. [1] reported that CVC-cycles have the potential to lead to 20% efficiency increase in contrast to the use of the Joulecycle. The CVC can be installed using can-annular combustion chambers that close one after the other when combustion is carried out and open to refill the combustion chambers with fresh gas. In consequence the flow-field in the last compressor stage becomes highly non-steady. A stable compressor operation is most important for gasturbine application. The vortex structures located at the end-wall regions generate

In this study, the effect of blowing angle on coefficients of aerodynamic of NACA0012 airfoil at Re=4×106 has been investigated. In the present research, the effect of three-dimensional blowing jet on the aerodynamic performance of the wing has been considered. The changes of lift and drag coefficients were studied by using the blowing near the leading edge of the airfoil for angles of attack of 12, 14, 16, 18 and 20 degrees. Due to the application of blowing through circular holes, a three-dimensional solution was used for the purpose of analysis and study, which will be computationally expensive. The analysis carried out in this case was performed with the assumption of incompressible and steady flow around a three-dimensional wing section in Fluent software. The results showed that the blowing has a negligible effect on the lift and drag coefficients at angles of attack less than 14 degrees. It is for this reason that only the effects of the blowing at high angles of attack are considered. The greatest increase in the lift coefficient and the greatest decrease in the drag coefficient occurs at the angle of attack of 16 degrees, which is the stall angle. The results showed that as the jet angle increases, the aerodynamic performance decreases.

Rotor blades can be found in many engineering applications, mainly associated with converting energy from fluids to work (or electricity). Rotor blade geometry is a key factor in the mechanical efficiency of the energy conversion process. For example, wind turbines' performance directly depends on the blade geometry and the wake flow formed behind them. We suggest to use a bioinspired blade based on the common swift wing. Common swift ( Apus apus ) is known to be a long-distance flyer, able to stay aloft for long periods of time by maintaining high lift and low drag. We study the near-wake flow characteristics of a freely rotating rotor with swept blades and its aerodynamic loads. These are compared with a straight-bladed rotor. The experiments were conducted in a water flume using particle image velocimetry (PIV) technique. Both blades were studied for four different flow speeds with freestream Reynolds numbers ranging from 23 000 to 41 000. Our results show that the near wake ...

The NACA0021 being a thick airfoil, possesses soft stall behavior with moderate maximum coefficient of lift (cl max). The present study focusses to improve aerodynamic performance using the moving surface boundary control. The modifications to airfoil include a rotating leading edge cylinder with airfoil aft body. The leading edge rotating cylinder injects momentum in top surface boundary layer thereby, keeping the flow attached in the otherwise adverse pressure gradient. The attached flow over top surface shall contribute to improve the airfoil aerodynamic performance in terms of lift, drag and stall angle. The present computational study focusses on modified airfoil performance for varying velocity ratios (i.e. ratio of tangential velocity of rotating cylinder and free stream velocity) between 0.0 and 1.78 at different airfoil angles of attack. The computational study clearly highlights improvement in modified airfoil aerodynamic performance in terms of coefficient of lift, drag, stall angle and clmax even at velocity ratios less than 1.0. The lift and drag characteristics of modified airfoil are found to be superior to base airfoil for velocity ratios beyond 0.356 and 0.7 respectively. The stall angle of attack for modified airfoil is also seen to increase linearly with velocity ratio. The stall angle of attack nearly doubles from 10 o for stationary leading edge to 19 o for velocity ratio of 1.78. The extent of momentum injection in boundary layer with varying cylinder speed is analysed by comparing the coefficient of pressure plots. The aerodynamic performance improvement thus achieved by momentum injection by low cost and practically feasible leading edge rotating cylinder in NACA 0021 promises its possible utilization for varied applications i.e. for low speed aircraft wing, wind turbine blades and hydrofoils.

In the present work, we study the aerodynamic effects of triangular vortex generators, as passive flow control devices, placed on the upper surface of an airfoil submitted to a low Reynolds number turbulent flow. In the experiments, different configurations of those devices have been studied. An Eppler 387 airfoil was used. The tests were performed in a turbulent boundary layer wind tunnel using a two component aerodynamic balance and flow visualisation systems. Turbulent flow characterisation was made by means of hot wire anemometry. Calculations of local turbulent intensity as well as temporal and spatial turbulent scales were made. Vortex generators were located at 10% and 20% of the airfoil chord from the leading edge, modifying Experimental study of vortex generators effects on low Reynolds number 51 its angle of incidence refereed to the free stream. The results show changes in the aerodynamic section coefficients, C l , C d and C l , for the different vortex generator configurations. Neither hysteresis effects, nor leading edge bubbles were found in the experiments.

Machining of hollow core honeycomb sandwich materia ls s a challenging job as the mechanical propertie s of various layers (skin, core) are quite dissimilar , and the conventional solid cutting tool experienc es a sudden change of conditions while machining that might lea d to damage on the tool/part. Although, abrasive wa terjets (AWJs) is highly efficient in the machining of adva nced composite materials due to their unique charac teristics, efficient machining of sandwich structures by AWJs needs many challenges to be addressed. This work pr esents various issues observed in AWJ machining of carbonand glassfiber skin based, aluminum sandwich str uctu e composite materials, and the limitations of AWJs in processing these exotic materials. Finally, possib le strategies for efficient machining of honeycomb structures wer e p oposed for future investigation.

The present article is the second part of a combined (experimental and computational) study on stall cells (SCs) on a rectangular wing. In the first part tuft data were used in order to geometrically characterise a stabilized SC resulting from a localised spanwise disturbance introduced by a zigzag (ZZ) tape. Here, pressure measurements on the model and in the wake, and aerodynamic polars at mid span are reported. The wing model had an aspect ratio (AR) value of 2, the Reynolds number was 10 6 and the range of angles of attack () was from-6 o to 16 o. Experimental results confirm previous findings. Furthermore, 2D and 3D RANS simulations are used in order to better understand the structure of SCs. 3D simulations reproduce the experimental data with a 3 0 delay in and permit a qualitative analysis. It is found that the SC vortices start normal to the wing surface and extend downstream in the wake; the evolution of the SC vortices in the wake is in strong interaction with the Separation Line Vortex and the Trailing Edge Line Vortex; as the SC vortex develops downstream in the wake, its centreline is contracted towards the SC centre; the wing wake is pushed upstream at the centre of the SC and downstream at the sides by the SC vortices; spanwise lift and drag distributions always attain their minimum at the SC centre.

This paper describes the structural design of an active flow-control experiment. The aim of the experiment is to investigate the increase in efficiency of an internally blown Coanda flap using unsteady blowing. The system uses tailor-made microelectromechanical (MEMS) pressure sensors to determine the state of the oncoming flow and an actuated lip to regulate the mass flow and velocity of a stream near a wall over the internally blown flap. Sensors and actuators are integrated into a highly loaded system that is extremely compact. The sensors are connected to a bus system that feeds the data into a real-time control system. The piezoelectric actuators using the d 33 effect at a comparable low voltage of 120 V are integrated into a lip that controls the blowout slot height. The system is designed for closed-loop control that efficiently avoids flow separation on the Coanda flap. The setup is designed for water-tunnel experiments in order to reduce the free-stream velocity and the system's control frequency by a factor of 10 compared with that in air. This paper outlines the function and verification of the system's main components and their development.

The close coupling of the ultra-high bypass ratio (UHBR) engine on a modern airliner poses a challenging task. The large engine nacelle diameter and a close coupling to the wing require slat cut-outs. In the attempt to remedy for the maximum lift loss, the Active Flow Control (AFC) is employed. The effect of steady suction and oscillatory blowing on local flow separation in the slat cut-out region downstream of a UHBR engine pylon is investigated by CFD URANS simulations. The simulation environment reflects the wind tunnel test conducted at the low speed wind tunnel at Tel-Aviv University. The validated CFD results are employed to assess the effects individual actuation mechanisms (steady suction, oscillatory blowing and a combination of both). Both investigated flow control mechanisms are effective in significant reduction of the flow separation. The AFC applied close to the leading edge in the slat cut-out region affects the flow field on large parts of the upper wing.

We investigated a non-steady compressor stator flow of the type that would be expected in a pulsed detonation engine. The effects on the stator vane of the last stator stage were discussed and results from the two-dimensional compressor stator cascade in Berlin are presented. Static pressure measurements showed periodic flow separation phenomena on the measurement blade with respect to the working-phase of a choking-device mounted in the wake of the cascade imposing the non-steady outflow condition. By means of active flow control (AFC) it was possible to avoid flow separation on the measurement blade. Furthermore a figure of merit was defined in order to rate the increase of static pressure recovery with respect to the AFC input. Using an optimized AFC setup the flow-field could be stabilized. 1 Introduction When applying pressure gaining combustion concepts to aero-engines or gas-turbines the impact on neighbouring machine parts needs to be taken into account. The constant volume combustion (CVC) is a promising concept in order to improve the overall efficiency of a gas turbine. Stathopoulos et al. [1] reported that CVC-cycles have the potential to lead to 20% efficiency increase in contrast to the use of the Joulecycle. The CVC can be installed using can-annular combustion chambers that close one after the other when combustion is carried out and open to refill the combustion chambers with fresh gas. In consequence the flow-field in the last compressor stage becomes highly non-steady. A stable compressor operation is most important for gasturbine application. The vortex structures located at the end-wall regions generate

Bu çalışmada NACA 23012, ag13 ve b737a kanat profilleri etrafındaki akış için doğrusal olmayan dinamik modelleme yapılarak, kaldırma/sürüklenme (l/d) değerinin iyileştirilmesi, sürüklenme/kaldırma (d/l) katsayısını azaltacak bir kontrol sistemi tasarlamak suretiyle gerçekleştirilmiştir. Kanat profilleri etrafındaki hava akışının dinamikleri, iki boyutlu Navier-Stokes denklemlerinin nümerik çözümlerinin yapılması ile elde edilmiştir. Çözümleri oluşturmak için kullanılan benzetim programı ise istenen ölçüm değerlerini okuyarak kanat üzerindeki eyleyici girişlerinden uygun kontrol girişlerini akış alanına uygulayabilecek şekilde geliştirilmiştir. Teknik temel olarak, kanat profili etrafındaki kontrolcü girişi noktaları belirlenmesi, bu noktalardan belirli bir girişe karşılık elde edilen ölçüm verilerinin kaydedilmesi ve bu giriş çıkış veri setine sistem tanılama uygulanarak sistemin dinamiklerinin kestiriminin yapılmasını temel alır. Kestirilen sistem dinamikleri kullanılarak kontrolcü...

A 10%-scale high-lift version of the Common Research Model (CRM-HL) and an Active Flow Control (AFC) version of the model equipped with a simple-hinged flap (CRM-SHL-AFC) were successfully tested. The tests were performed in the 14-by 22-Foot Subsonic Tunnel (14x22) at the NASA Langley Research Center (LaRC). The CRM-HL has a set of 37° inboard and outboard single-element Fowler flaps. The CRM-SHL-AFC has a set of 50° inboard and 55° outboard simple-hinged flaps equipped with integrated modular AFC cartridges on the flap shoulder. Both high-lift configurations share the same 30° slats and engine nacelle. Three new types of AFC devices were examined: the Double-Row Sweeping Jets (DRSWJ), the Alternating Pulsed Jets (APJ), and the High Efficiency Low Power (HELP) actuators. The DRSWJ and the APJ actuators used two rows of unsteady jets, whereas the HELP actuators used a combination of unsteady and steady jets, to overcome strong adverse pressure gradients while minimizing the mass flow usage. Nozzle pressure ratio, mass flow consumption and the power coefficient, which takes account of both supply air pressure and mass flow usage for the actuators, were used for judging the performance efficiency of the AFC devices. A prestall lift performance degradation for the CRM-HL configuration was resolved with a properly placed nacelle chine. The configuration with nacelle chine was chosen as the representative reference conventional high-lift case for comparison with the CRM-SHL-AFC. The AFC-induced lift coefficient increment (DCL) was maintained for the entire lift curve over the CRM-SHL-AFC case with no AFC for almost all flow-control cases examined. The lift curve of the reference CRM-HL have a slightly steeper slope compared to those of the CRM-SHL-AFC configurations. The HELP actuation concept was extremely effective in controlling flow separation in the "linear region" of the curves comparing lift coefficient to mass flow rate. The HELP actuation achieved a targeted DCL of 0.50 using a moderate amount of mass flow and supply air pressure. The CRM-SHL-AFC configuration equipped with HELP actuation was able to match or exceed the lift performance of the reference conventional high-lift configuration (i.e., CRM-HL equipped with a nacelle chine), thus meeting the NASA Advanced Air Transport Technology (AATT) project goal.