Accuracy Investigation of Active Flow Control Using Synthetic Jets

2015 ◽  
Vol 741 ◽  
pp. 475-480
Author(s):  
Na Gao ◽  
Chen Pu ◽  
Bao Chen
Keyword(s):  
Flow Control ◽  
Velocity Distribution ◽  
Active Flow Control ◽  
Flow Fields ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Experimental Results ◽  
Center Line ◽  
Mean Velocity ◽  
The Mean

2nd order implicit format is implemented in the Navier-Stokes code to deal with instantaneous item unsteady flows. Three simulations are made to testify the method on flow control. First, the external flow fields of synthetic jets are simulated, the mean velocity on the center line, the jet width and velocity distribution are compared well with experimental results. Secondly, the flow fields of synthetic jet in a crossflow are simulated, orifice slot, the mean velocity on the center line and velocity distribution are compared well with experimental results. Finally, the flow control experiments on separation of airfoil are simulated, control methods include steady suction and synthetic jets. Both methods show their ability to favorably effect the flow separation, shortening the length of separation bubble and improving the pressure levels in separation areas in different degrees.

Active Separation Control of Flow Over a Wall-Mounted Hump Using Zero-Efflux Synthetic Jet

2008 ◽  
Author(s):  
Subhadeep Gan ◽  
Urmila Ghia ◽  
Karman Ghia
Keyword(s):  
Flow Control ◽  
Turbulence Modeling ◽  
Separated Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Experimental Results ◽  
Separation Control ◽  
Mean Flow ◽  
Modeling Approaches ◽  
Baseline Case

Most practical flows in engineering applications are turbulent, and exhibit separation which is generally undesirable because of its adverse effects on performance and efficiency. Therefore, control of turbulent separated flows has been a topic of significant interest as it can reduce separation losses. Often, flow control work employs passive techniques to manipulate the flow. These approaches do not require any additional energy source to achieve the control, but are accompanied by additional viscous losses. However, it is more desirable to employ active techniques as these can be turned on and off, depending on the flow control requirement. Use of synthetic jets has gained popularity in recent times for active flow control because of their ability to transfer linear momentum to the flow system without net-mass injection across the boundary in the vicinity of separation. The present work is Case 3 of the 2004 CFD Validation on Synthetic Jets and Turbulent Separation Control Workshop, http://cfdval2004.larc.nasa.gov/case3.html, conducted by NASA for the flow over a wall-mounted hump. This flow is characterized by a simple geometry, but, nevertheless, is rich in many complex flow phenomena such as shear layer instability, separation, reattachment, and vortex interactions. The baseline case and control case with steady suction has been successfully simulated by Gan et al., (2007 and 2008). The present work is focused on implementing a synthetic jet to achieve flow control. The jet was simulated by implementing an analytical sinusoidal velocity boundary condition at the surface of the jet exit. The jet-exit velocity has a parabolic profile across the control slot, and a sinusoidal temporal variation. The flow is simulated at a Reynolds number of 371,600, based on the hump chord length, C, and a Mach number of 0.04. The synthetic control jet exits through a slot located at approximately 0.65 C. Solutions are obtained using the three-dimensional RANS SST turbulence model, and the DES and LES turbulence modeling approaches. Multiple turbulence modeling approaches help to ascertain what techniques are most appropriate for capturing the physics of this complex separated flow. The location of the reattachment behind the hump is compared with experimental results. The successful control of this turbulent separated flow leads to a reduction in the reattachment length, compared with the baseline case. Velocity contours at several streamwise locations are presented and compared to experimental results. Mean flow parameters such as pressure coefficients and skin-friction coefficient are presented. The paper includes detailed comparisons of turbulent parameters such as the Turbulent Kinetic Energy (TKE) and Reynolds stress profiles, with experimental results. Instantaneous vorticity contours are presented from the simulations. Discussion are presented of the effects of synthetic jet control on flow separation and reattachment and the resulting enhancement of performance and efficiency.

scholarly journals Active flow control by means of synthetic jets on a highly loaded compressor cascade

2011 ◽  
Vol 225 (7) ◽  
pp. 897-908 ◽  
Author(s):  
V Zander ◽  
M Hecklau ◽  
W Nitsche ◽  
A Huppertz ◽  
M Swoboda
Keyword(s):  
Flow Control ◽  
Large Scale ◽  
Active Flow Control ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Actuation Frequency ◽  
Active Flow ◽  
Highly Loaded

This article presents the potential of active flow control to increase the aerodynamic performance of highly loaded turbomachinery compressor blades. Experimental investigations on a large-scale compressor cascade equipped with 30 synthetic jet actuators mounted to the sidewalls and the blades themselves have been carried out. Results for a variation of the inflow angle, the jet amplitude, and the actuation frequency are presented. The wake measurements show total pressure loss reductions of nearly 10 per cent for the synthetic jet actuation. An efficiency calculation reveals that the energy saved by actuation is nearly twice the energy consumption of the synthetic jets.

Active Flow Control on Low-Pressure Turbine Blades Using Synthetic Jets

2006 ◽  
Author(s):  
Shirdish Poondru ◽  
Urmila Ghia ◽  
Karman Ghia
Keyword(s):  
Flow Control ◽  
Air Force ◽  
Active Flow Control ◽  
Reynolds Numbers ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Main Flow ◽  
Control Mechanisms ◽  
Low Pressure Turbine ◽  
Active Flow

The operating Reynolds numbers (Re) for a low-pressure turbine (LPT) in an aircraft engine can drop below 25,000 during high-altitude cruise conditions. At these low Reynolds numbers, the boundary layer on the LPT blade is largely laminar, and is susceptible to separation on the aft portion of the blade suction surface. This separation is detrimental and causes a significant loss in the engine efficiency. The objective of the current research is to control this separation, and minimize the associated losses by numerically implementing an active flow control strategy. Unlike passive flow control techniques, active flow control (AFC) techniques can be turned on and off depending on the requirement for flow control. In the present paper, we numerically investigate the flow through an LPT cascade at a chord inlet Reynolds number of 25,000 with active separation control using synthetic jets and synthetic vortex-generator jets (VGJ’s). Synthetic jets hold an advantage over steady or pulsed jets in that they require no net mass flow, i.e., synthetic jets are formed entirely from the working fluid of the flow system in which they are deployed and, thus, can transfer linear momentum to the flow system without net mass injection across the flow boundary. In the LPT environment, this means that no compressor bleed air is required. While LPT separation control using steady and pulsed VGJs has been numerically investigated before, AFC on an LPT blade by synthetic jets and synthetic VGJs has not yet been numerically investigated. The geometrical difference between a synthetic jet and synthetic VGJ is the angle at which the jet enters the main flow. A synthetic jet enters the main flow normal to the surface, and on the other hand, a synthetic VGJ enters at a certain angle to the wall (pitch angle) and at a certain angle to the main flow (skew angle). For the present case, the VGJs are oriented at 30° to the surface and 90° to the main flow. In addition to the angle at which these two jets enter the main flow, these flow control mechanisms differ in the way they delay or avoid separation. Synthetic jets generate turbulent spots which energize the flow, whereas synthetic VGJ’s generate streamwise vortices which enhance mixing. The relative magnitudes of the effects of turbulence and streamwise vortices in enhancing mixing are being investigated. The results for both control mechanisms will be compared to each other, and with experimental data. An MPI-based higher-order accurate, Chimera version of the FDL3DI flow solver developed by the Air Force Research Laboratory at Wright Patterson Air Force Base, is extended for the present turbomachinery application.

scholarly journals Global energy fluxes in turbulent channels with flow control

2018 ◽  
Vol 857 ◽  
pp. 345-373 ◽  
Author(s):  
Davide Gatti ◽  
Andrea Cimarelli ◽  
Yosuke Hasegawa ◽  
Bettina Frohnapfel ◽  
Maurizio Quadrio
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Energy Dissipation ◽  
Velocity Field ◽  
Flow Control ◽  
Reynolds Shear Stress ◽  
Power Input ◽  
Energy Fluxes ◽  
Mean Velocity ◽  
The Mean

This paper addresses the integral energy fluxes in natural and controlled turbulent channel flows, where active skin-friction drag reduction techniques allow a more efficient use of the available power. We study whether the increased efficiency shows any general trend in how energy is dissipated by the mean velocity field (mean dissipation) and by the fluctuating velocity field (turbulent dissipation). Direct numerical simulations (DNS) of different control strategies are performed at constant power input (CPI), so that at statistical equilibrium, each flow (either uncontrolled or controlled by different means) has the same power input, hence the same global energy flux and, by definition, the same total energy dissipation rate. The simulations reveal that changes in mean and turbulent energy dissipation rates can be of either sign in a successfully controlled flow. A quantitative description of these changes is made possible by a new decomposition of the total dissipation, stemming from an extended Reynolds decomposition, where the mean velocity is split into a laminar component and a deviation from it. Thanks to the analytical expressions of the laminar quantities, exact relationships are derived that link the achieved flow rate increase and all energy fluxes in the flow system with two wall-normal integrals of the Reynolds shear stress and the Reynolds number. The dependence of the energy fluxes on the Reynolds number is elucidated with a simple model in which the control-dependent changes of the Reynolds shear stress are accounted for via a modification of the mean velocity profile. The physical meaning of the energy fluxes stemming from the new decomposition unveils their inter-relations and connection to flow control, so that a clear target for flow control can be identified.

New space-averaging procedure for inhomogeneous flow fields using balance equation formulations

2006 ◽  
Vol 220 (9) ◽  
pp. 1363-1374
Author(s):  
S Wattananusorn
Keyword(s):  
Compressible Flows ◽  
Incompressible Flows ◽  
Flow Fields ◽  
Coupling Factor ◽  
Balance Equations ◽  
Mean Velocity ◽  
New Space ◽  
Inhomogeneous Flow ◽  
The Mean ◽  
Dependent Flow

This paper features the possibility of averaging space-dependent flow fields using a coupling factor that links the equations of momentum and energy. The scheme is applied to the mean velocity, which is derived straightforwardly through the continuity equation. It creates a small imbalance, which can be eliminated later completely. Smaller discrepancies in the integration of systems of balance equations for inhomogeneous flow are the consequence. The procedure is verified on various flow patterns, and comparisons are made with other conventional methods and with some available experimental data. Despite investigating only numerical examples of incompressible flows here, the technique, in principle, is capable of dealing with compressible flows as well. Furthermore, the proposed method discards some variables required in other techniques while still providing useful and acceptable results for practical problems.

On Turbulent Flow Between Parallel Plates

1953 ◽  
Vol 20 (1) ◽  
pp. 109-114
Author(s):  
S. I. Pai
Keyword(s):  
Turbulent Flow ◽  
Velocity Distribution ◽  
Poiseuille Flow ◽  
The Other ◽  
Turbulent Velocity ◽  
Parallel Plates ◽  
Mean Velocity ◽  
Reynolds Equations ◽  
Mean Pressure ◽  
The Mean

Abstract The Reynolds equations of motion of turbulent flow of incompressible fluid have been studied for turbulent flow between parallel plates. The number of these equations is finally reduced to two. One of these consists of mean velocity and correlation between transverse and longitudinal turbulent-velocity fluctuations u 1 ′ u 2 ′ ¯ only. The other consists of the mean pressure and transverse turbulent-velocity intensity. Some conclusions about the mean pressure distribution and turbulent fluctuations are drawn. These equations are applied to two special cases: One is Poiseuille flow in which both plates are at rest and the other is Couette flow in which one plate is at rest and the other is moving with constant velocity. The mean velocity distribution and the correlation u 1 ′ u 2 ′ ¯ can be expressed in a form of polynomial of the co-ordinate in the direction perpendicular to the plates, with the ratio of shearing stress on the plate to that of the corresponding laminar flow of the same maximum velocity as a parameter. These expressions hold true all the way across the plates, i.e., both the turbulent region and viscous layer including the laminar sublayer. These expressions for Poiseuille flow have been checked with experimental data of Laufer fairly well. It also shows that the logarithmic mean velocity distribution is not a rigorous solution of Reynolds equations.

Active flow control, for fixed wings, using synthetic jets

2022 ◽  
Author(s):  
Marcel Ilie ◽  
Jackson Asiatico ◽  
Matthew Chan
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Synthetic Jets ◽  
Active Flow

Numerical Investigations of Active Flow Control Using Synthetic Jets on a Highly Loaded Compressor Stator Cascade

2010 ◽  
Author(s):  
Christoph Gmelin ◽  
Mathias Steger ◽  
Vincent Zander ◽  
Wolfgang Nitsche ◽  
Frank Thiele ◽  
...  
Keyword(s):  
Separation Bubble ◽  
Active Flow Control ◽  
Suction Side ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Navier Stokes ◽  
Compressor Cascade ◽  
Time Resolved ◽  
Laminar Separation ◽  
Zero Net Mass Flux

Time-resolved Reynolds-Averaged Navier-Stokes simulations of a 3D stator compressor cascade are performed. At the design point of the airfoil under investigation, pronounced secondary flow effects are observed. Strong corner vortices emerge from the casing walls and the flow separates from the blade suction side towards the trailing edge. Transition from laminar to turbulent flow occurs within a laminar separation bubble. Using a commercial CFD software, the influence of the spatial resolution is investigated by means of a spanwise coarsening and refinement of the created mesh. Zero net mass flux synthetic jet actuation is used to control the separated regions. The work presents a variation of the temporal discretization and an analysis of the driving parameters of the actuation.

Effective Range of Micro and Synthetic Jets for Flow Control

2005 ◽  
Author(s):  
Mehti Koklu ◽  
Nurhak Erbas ◽  
Oktay Baysal
Keyword(s):  
Flow Control ◽  
Moving Boundary ◽  
Rarefied Gas ◽  
Oscillation Amplitude ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Navier Stokes ◽  
Rarefied Gas Flows ◽  
Design Variables ◽  
Primary Focus

Effectiveness of two-dimensional synthetic jet is studied using numerical simulations. A Navier-Stokes (NS) solver for moving and deforming meshes has been modified to investigate numerically the diaphragm-driven flow in and out of two synthetic jet cavity geometries. Compressible flow simulations are required for rarefied gas flows to accurately predict the micro flow field. The solver is modified to accommodate slip wall boundary condition proposed in literature for micro scale flow problems. The piezoelectric-driven diaphragm of the cavity is modeled in a realistic manner as a moving boundary to accurately compute the flow inside the jet cavity. The primary focus of the proposed paper will be on the analysis of the design space determined by the geometric and flow-type design variables that identify the effectiveness of the synthetic jet by means of the orifice jet velocity and local jet momentum rate. The design variables are the membrane oscillation frequency (f), membrane oscillation amplitude (A), orifice width (d), and membrane width (W). The present computations for jet discharging into quiescent medium reveal that these variables have determining effects on the flow control parameters, which are the jet exit velocity, local momentum rate, as well as vortex shedding from the orifice.

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