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Low Reynolds unsteady flow simulation around NACA0012 airfoil with active flow control

MECCANICA 2018年第14期53卷 3457-3476页

作者： Akbarzadeh, P. Lehdarboni, A. Askari Derazgisoo, S. M. Shahrood Univ Technol Fac Mech & Mechatron Engn P Box *** Shahrood Semnan Iran

This research numerically elucidates the effects of suction and blowing on the enhancement of unsteady aerodynamic characteristics of flows and their corresponding impact on stall delay over the well-known NACA0012 airfoil at various angles of attack (12 <= AOA <= 20) under low Reynolds numbers. For this purpose, an in-house solver written in C?? is developed. The numerical code utilizes the Jameson's cell-centered finite volume numerical method accompanied by a progressive power-law preconditioning approach to suppress the stiffness of the governing equations. Many numerical simulations are performed over the suction-blowing control parameters, namely, the slot location (Lj), suction/ blowing amplitudes (Aj), and suction/blowing angle (hj). Most of the analyses are based on the measurements of the unsteady aerodynamic characteristics behaviors (such as lift, drag, moment coefficients, and stall phenomena) over the airfoil. The numerical results confirm that the unsteady behavior of the flow (vortex shedding) is weakened or approximately removed when suction is used, especially near the leading edge. In all of the test cases, the ratio of the average lift coefficient to the average drag coefficient increases with increasing suction and blowing amplitudes, except in the case of perpendicular blowing. Furthermore, the blowing is more sensitive to the blowing angle compared to the suction. From the suction and blowing results, it is concluded that the former has a more positive impact on the lift and drag characteristics, especially in the case of incompressible flow at Low-Reynolds regimes.

关键词： active flow control Suction and Blowing Unsteady aerodynamic characteristics Power-law preconditioning method

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The Influence of Spurious Periodicity on the flow Characteristics of a Separated Turbulent Boundary Layer with and Without active flow control

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flow TURBULENCE AND COMBUSTION 2024年第2期112卷 459-482页

作者： Asgari, Ehsan Saeedi, Mohammad Dalhousie Univ Dept Mech Engn Halifax NS Canada

In this study, we have investigated the effects of inflow spurious periodicity on a turbulent boundary layer subjected to a weak pressure gradient due to a gently backward ramp utilizing wall-resolved large-eddy simulation. The spurious periodicity is generated through repeating segments of inflow data produced via a long boundary layer precursor simulation. Using a short segment of inflow data and recycling it while introduces a spurious periodicity, can help to reduce the computational cost of the precursor simulation as well as the storage needed to record the massive data. However, there is no quantitative analysis as to how far the results are affected by the spurious periodicity in case of a separated turbulent boundary layer. This study compares several cases with various inflow segment lengths with respect to a reference case with no periodicity. The inflow segments are created by truncating the reference case and thus an intrinsic disturbance is associated with them. An additional case without the disturbance is also considered to examine the latter's influence on the results. First- and second-order flow statistics are assessed, and spectral analysis is conducted to scrutinize the impact of spurious periodicity. An additional second-order parameter is introduced as an indicator of the spurious periodicity influence. Finally, an especial configuration with active flow control using a synthetic jet actuator is investigated with and without the spurious periodicity. This will help to assess if the dominant frequency of the active flow control is affected by recycling inflow data.

关键词： Spurious periodicity Large-eddy simulation Turbulence Synthetic jet active flow control

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Flight and Wind-Tunnel Tests of Closed-Loop active flow control

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JOURNAL OF AIRCRAFT 2013年第5期50卷 1605-1614页

作者： King, Rudibert Heinz, Notger Bauer, Matthias Grund, Thomas Nitsche, Wolfgang Tech Univ Berlin Chair Measurement & Control D-10623 Berlin Germany Tech Univ Berlin Dept Aeronaut & Astronaut D-10623 Berlin Germany

Closed-loop active flow control is applied in wind-tunnel tests to an industry-relevant civil aircraft half-model designed by Airbus and in full-scale free-flight experiments with a Stemme S10 glider. The focus of this contribution is on closed-loop control. Moreover, it is shown that our approach can be used for very different setups. For this, the modeling of the dynamic responses of the two systems and the synthesis of robust controllers are compared. For the highly three-dimensional wind-tunnel model, differential pressures are used as surrogate control variables as a correlation with the lift can be described by a lookup table. Two control inputs, pulsed blowing, and two output variables are exploited. In the glider study, with a profile that experiences a mostly two-dimensional flow, an approximate pressure gradient is used instead as a single output to avoid the necessity of such a lookup table. active flow control is done again, exploiting pulsed blowing. For the controller synthesis, both in the single-input single-output and in the multivariable cases, the same approach is used, showing its versatility. In both setups, the closed-loop controllers succeed in adjusting the control inputs such that changing reference signals are followed, and the influence of disturbances are attenuated. For the civil aircraft model, completely new landing scenarios can be proposed using the closed-loop controller.

关键词： Wind Tunnel Models active flow control Proportional control Airbus Multiple Input Multiple Output Two Dimensional flow Civil Aircraft Dynamic Response Lift Coefficient Flight Testing

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Effects of turbulence boundary conditions on Spalart-Allmaras RANS simulations for active flow control applications

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MECCANICA 2024年第12期59卷 2283-2294页

作者： Tousi, Navid Monshi Bergada, Josep M. Mellibovsky, Fernando Univ Politecn Cataluna Dept Fluids Mech Barcelona 08034 Spain Univ Politecn Cataluna Dept Phys Aeronaut Div Barcelona 08034 Spain

We assess the suitability of Reynolds-Averaged Navier-Stokes (RANS) simulation using the Spalart-Allmaras (SA) turbulence model as a closure in analysing the performance of fluidic active flow control (AFC) applications. In particular, we focus on the optimal set of actuation parameters found by Tousi et al. (Appl Math Model, 2021) and Tousi et al. (Aerospace Sci Technol 127:107679, 2022) for a SD7003 airfoil at a Reynolds number Re=6x10(4 )and post-stall angle of attack alpha=14(degrees) fitted with a Synthetic Jet Actuator (SJA). The Large Eddy Simulation (LES) presented in that work is taken as the reference to identify the best choice of boundary conditions for the turbulence field nu at both domain inlet and jet orifice in two-dimensional SA-RANS computations. Although SA-RANS is far less accurate than LES, our findings show that it can still predict macroscopic aggregates such as lift and drag coefficients quite satisfactorily and at a much lower computational cost, provided that turbulence levels of the actuator jet are set to a realistic value. An adequate value of nu is instrumental in capturing the correct flow behaviour of the reattached boundary layers for close-to-optimal actuated cases. This validates the use of RANS-SA as a reliable and cost-effective simulation method for the preliminary optimisation of SJA parameters in AFC applications, provided that thorough sensitivity analysis on turbulence-related boundary conditions is performed. Given the strong sensitivity of flow detachment on the laminar or turbulent nature of boundary layers, our results suggest that such analyses are particularly indispensable for vastly separated flow scenarios in general, notably for bluff bodies at moderate transcritical Reynolds numbers.

关键词： active flow control RANS-Spalart Allmaras Turbulence parameter tuning Optimisation

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Research at DLR Gottingen on bluff body aerodynamics, drag reduction by wake ventilation and active flow control

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JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS 2001年第14-15期89卷 1201-1218页

作者： Grosche, FR Meier, GEA DLR Inst Stromungsmech Deutsch Zentrum Luft & Raumfahrt eV German Aerosp CtrInst Aerodynam & Flow Technol D-37073 Gottingen Germany

This paper outlines some experimental investigations on aerodynamics of bluff bodies which have been carried out at the former DLR Institute of Fluid Mechanics. now Institute of Aerodynamics and flow Technology. Examples given here include (a) drag reduction by passive ventilation of the wake of the body, (b) reduction of the drag of automobiles by shape optimisation to eliminate or at least decrease trailing vortices, (c) optimisation of front and rear ends of high speed trains, (d) determination of the main sources of aerodynamic noise of high velocity trains which result from unsteady flow separations, (e) experiments on active flow control to delay flow separation. (C) 2001 Published by Elsevier Science Ltd.

关键词： flow separation drag reduction aerodynamic noise active flow control passive wake ventilation

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Validation of PANS and active flow control for a generic truck cabin

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JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS 2017年 171卷 148-160页

作者： Minelli, G. Hartono, E. Adi Chernoray, V. Hjelm, L. Basara, B. Krajnovic, S. Chalmers Univ Technol Dept Mech & Maritime Sci Gothenburg Sweden Volvo Trucks AB Gothenburg Sweden AVL List GmbH Adv Simulat Technol Hans List Pl A-8020 Graz Austria

This paper presents a drag reduction study using active flow control (AFC) on a generic bluff body. The model consists of a simplified truck cabin, characterized by sharp edge separation on top and bottom edges and pressure induced separation on the two other rounded vertical front corners. The pressure induced separation reproduces the flow detachment occurring at the front A-pillar of a real truck (Schuetz, 2015). The prediction of the flow field by partially averaged Navier-Stokes (PANS) simulations, conducted on a relatively coarse mesh, is validated against wind tunnel data (pressure measurements and particle image velocimetry (PTV)) and resolved large eddy simulations (LES) data. The Reynolds number for both simulations and experiments is Re = 5 x 10(5) (which corresponds to 1/6 of a full scale truck Re) based on the inlet velocity U-inf and the width of the model W = 0.4m. A validation of PANS results is followed by a CFD study on the actuation frequency that minimizes the aero-dynamic drag and suppresses the side recirculation bubbles. PANS accurately predicts the flow field measured in experiments and predicted by a resolved LES. The side recirculation bubble of a simplified truck cabin model is suppressed almost completely and a notable drag reduction by means of AFC is observed.

关键词： Partially averaged Navier-Stokes PANS Large eddy simulation LES Experiments active flow control AFC Proper orthogonal decomposition POD Truck Drag reduction Vehicle aerodynamics

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Prediction of active flow control performance on airfoils and wings

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AEROSPACE SCIENCE AND TECHNOLOGY 2004年第5期8卷 401-410页

作者： Ekaterinaris, JA FORTH Inst Appl & Computat Math Iraklion 71110 Crete Greece

A numerical investigation of active flow control, which can offer significant improvements to aircraft wing, helicopter and wind-turbine rotor performance by suppressing detrimental effects of separated flow, is presented. Numerical simulations of pulsating jet flow control applied on airfoils and wings at low speed, high Reynolds number turbulent flow and fixed angles of incidence are carried out. Pulsating jet active flow control is applied as a surface boundary condition and the flow is time-dependent. It was found that fine grid resolution is required to capture the pulsating jet and its interaction with the boundary layer. Efficient, implicit, time-accurate numerical methods for unsteady RANS of incompressible flow are used to overcome the stringent stability limitations imposed by small grid spacing. A widely tested one-equation turbulence model is used for the prediction of the complex, unsteady flowfields. It is found that active flow control can enhance aerodynamic performance by reducing the adverse effects of separated flow. The effect of pulsation frequency, and jet exit velocity on flow control is investigated. (C) 2004 Elsevier SAS. All rights reserved.

关键词： active flow control separated flow control drag reduction

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Ships with ventilated cavitation in seaways and active flow control

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APPLIED OCEAN RESEARCH 2015年 50卷 163-172页

作者： Amromin, E. L. Mechmath LLC Federal Way WA 98003 USA

Bottom ventilated cavitation has been proven as a very effective drag reduction technology for river ships and planning boats. The ability of this technology to withstand the sea wave impact usual for seagoing ships depends on the ship bottom shape and could be enhanced by some active flow control devices. Therefore, there is the need in numerical tools to estimate the effects of bottom changes and to design such devices. The fundamentals of active flow control for the ship bottom ventilated cavitation are considered here on the basis of a special model of cavitating flows. This model takes into account the air compressibility in the cavity, as well as the multi-frequency nature of the incoming flow in wavy seas and of the cavity response on perturbations by incoming flow. The numerical method corresponding to this model was developed and widely manifested with an example of a ship model tested in a towing tank at Froude numbers between 0.4 and 0.7. The impact of waves in head seas and following seas on cavities has been studied in the range of wavelengths from 0.45 to 1.2 of the model (or ship) length. An oscillating cavitator-spoiler was considered as the flow controlling devices in this study. The oscillation magnitude and the phase shift between cavitator oscillation and the incoming waves have been varied to determine the best flow control parameters. The main results of the provided computational analysis include oscillations of cavity surface, of the pressure in cavity and of the moment of hydrodynamic load on the cavitator. The major part of computations has been carried out for the flap oscillating at the frequency coinciding with the wave frequency, but the effect of a frequency shift is also analyzed. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Hydrodynamics Waves Ship drag reduction active flow control

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High-Lift Performance Enhancement Using active flow control

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AIAA JOURNAL 2020年第10期58卷 4228-4242页

作者： DeSalvo, Michael Whalen, Edward Glezer, Ari Georgia Inst Technol Woodruff Sch Mech Engn Atlanta GA 30332 USA Boeing Co Boeing Res & Technol Hazelwood MO 63042 USA

The aerodynamic performance of conventional high-lift systems is typically achieved using multi-element flap configurations with cross-stream gaps that necessitate the use of complex positioning mechanisms with significant penalties in terms of weight, part count, and fabrication cost. In the present investigation, the performance of a high-lift airfoil in Fowler flap and simple flap configurations is enhanced using active aerodynamic flow control. Actuation is applied using a spanwise arrays of fluidically oscillating jets located upstream and downstream of the leading edge of the flap that increase the extent of flow attachment along the surface of the flap at deflections of up to 60 degrees. Actuation leads to significant improvement in the performance of the Fowler flap compared with an optimized baseline configuration (CL increased by up to 30%) and enables the high-lift performance of a single-element, simple flap without a cross-stream gap to match or exceed the performance of the optimized baseline Fowler configuration. It is also shown that incorporating a cross-stream gap with the simple flap enables increased lift at reduced actuation levels.

关键词： active flow control Trailing Edge Flap Airfoil Aerodynamic Performance Aerodynamic flows Adverse Pressure Gradient Boundary Layer flow Leading Edge Slat Particle Image Velocimetry Wind Tunnel Interference

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Extensions of adaptive slope-seeking for active flow control

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART I-JOURNAL OF SYSTEMS AND control ENGINEERING 2008年第I5期222卷 309-322页

作者： Henning, L. Becker, R. Feuerbach, G. Muminovic, R. King, R. Brunn, A. Nitsche, W. Tech Univ Berlin Dept Measurement & Control D-10623 Berlin Germany Tech Univ Berlin Dept Aeronaut & Astronaut D-10623 Berlin Germany

To speed up gradient estimation in a slope-seeking controller two different modifications are proposed in this study. In a first approach, the gradient estimation is based on a locally identified black-box model. A further improvement is obtained by applying an extended Kalman filter to estimate the local gradient of an input-output map. Moreover, a simple method is Outlined to adapt the search radius in the classical extremum- and slope-seeking approach to reduce the perturbations near the optimal state. To show the versatility of the slope-seeking controller for flow control applications two different wind tunnel experiments are considered, namely with a two-dimensional bluff body and a generic three-dimensional car model (Ahmed body).

关键词： active flow control extremum-seeking control slope-seeking control Kalman filter least square Ahmed body bluff body

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