LES of Active Separation Control on Bluff Bodies by Steady Blowing

2010 ◽  
Author(s):  
Sa´ndor Eichinger ◽  
Frank Thiele ◽  
Erik Wassen
Keyword(s):  
Flow Control ◽  
Aerodynamic Drag ◽  
Active Flow Control ◽  
Rear Surface ◽  
Base Flow ◽  
Back Surface ◽  
Bluff Bodies ◽  
Control Approach ◽  
Vertical Extension ◽  
Active Flow

An active flow control approach was investigated in order to reduce the aerodynamic drag of a generic square-backed vehicle. The investigations were carried out at a Reynolds number of ReL = 500,000. Large Eddy Simulations were performed which are suitable for time dependent flows around vehicles with large coherent structures. After the base flow simulations active flow control was applied in order to achieve drag reduction using steady blowing through small slits near the edges of the rear surface. The blowing velocity was equal to the inflow velocity (vblow = U0), and the blowing angle was changed from θ = 0° to θ = 60°. It is shown that these control techniques can achieve a maximum drag decrease for the θ = 45° control version of around 12%. Additionally the effect of moving floor was studied and comparison was made for the baseline and for the 45° flow control variant. It was found that the stagnation point on the rear surface moves upwards, and the vertical extension of the wake section reduces, so the evolving pressure level on the back surface increases. Finally a study of the blowing velocity was performed, changing vblow = 0.25U0 until vblow = 2.25U0 at θ = 45° blowing angle. An efficiency optimum was found around vblow = 1.25U0.

Transition Modeling Effects on the Simulation of a Stator Cascade With Active Flow Control

2008 ◽  
Author(s):  
Dirk Mertens ◽  
Frank Thiele ◽  
Marius Swoboda ◽  
Andre´ Huppertz
Keyword(s):  
Flow Control ◽  
Mass Flow ◽  
Active Flow Control ◽  
Base Flow ◽  
Experimental Measurements ◽  
Transition Model ◽  
Transition Effects ◽  
Transition Modeling ◽  
Active Flow ◽  
Varying Mass

An investigation of a stator cascade is undertaken by means of steady 3D RANS simulations, the focus of which is on two computational setups. The first takes transition effects into account using a correlation-based transition model as suggested by Abu-Ghannam and Shaw, while the second is considered to be fully turbulent. In a first step the base flow is validated by experimental measurements, followed by configurations employing active flow control by means of steady jets with varying mass flow. By investigating the differences arising due to the varying level of modeling complexity the necessity of using a transition model can be illustrated.

Evaporator Superheat Regulation via Emulation of Semi-Active Flow Control

2009 ◽  
Author(s):  
Matthew Elliott ◽  
Bryan P. Rasmussen
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Control Device ◽  
Operating Conditions ◽  
Limiting Factor ◽  
Efficient Operation ◽  
Control Approach ◽  
Active Feedback ◽  
Vapor Compression Cooling ◽  
Active Flow

Proper regulation of evaporator superheat is essential to ensuring safe and efficient operation of vapor compression cooling systems. Typical mechanical control devices may behave poorly under transient disturbances or as operating conditions vary, degrading system performance. Electronic expansion valves partially alleviate these problems by allowing more sophisticated control approaches, but frequent valve adjustments raise concerns about device longevity. A cascaded control approach to superheat regulation has been shown to provide significant improvements in superheat control, utilizing a hybrid of mechanical (passive) and electronic (active) feedback devices. This paper examines the emulation of a semi-active flow control device using a MEMs based actuator with high bandwidth, few moving parts, and no risk of fatigue failure. Experimental evaluation reveals this to be a comparable approach to the hybrid valve design. Moreover, further examination reveals that actuator characteristics are the limiting factor in achieving similar levels of performance using standard electronic valves.

Active Flow Control of the 3D Separation on a Ahmed Body Using Steady Microjet Arrays

2010 ◽  
Author(s):  
S. Aubrun ◽  
F. Alvi ◽  
A. Leroy ◽  
A. Kourta
Keyword(s):  
Flow Control ◽  
Aerodynamic Drag ◽  
Separation Bubble ◽  
Active Flow Control ◽  
Aerodynamic Load ◽  
Flow Topology ◽  
Rear Window ◽  
Slant Angle ◽  
Control Approach ◽  
Ahmed Body

A model of a generic vehicle shape, the Ahmed body with a slant angle of 25°, is equipped with an array of blowing steady microjets 6mm downstream of the separation line between the roof and the slanted rear window. The goal of the present study is to evaluate the effectiveness of this actuation method in reducing the aerodynamic drag, by reducing or suppressing the 3D closed separation bubble located on the slanted surface. The efficiency of this control approach is quantified with the help of aerodynamic load measurements. The changes in the flow field when control is applied are examined using PIV measurements and skin friction visualizations. By activating the steady microjet array, the drag coefficient was reduced by 9 to 11%, depending on the Reynolds number. The modification of the flow topology under progressive flow control is particularly studied.

Active Flow Control on Bluff Bodies with Distinct Separation Locations

2002 ◽  
Author(s):  
Per Kjellgren ◽  
Dino Cerchie ◽  
Lachlan Cullen ◽  
Israel Wygnanski
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Bluff Bodies ◽  
Active Flow ◽  
Distinct Separation

Reducing Energy Consumption of Ground Vehicles by Active Flow Control

2010 ◽  
Author(s):  
Miles Bellman ◽  
Ramesh Agarwal ◽  
Jonathan Naber ◽  
Lee Chusak
Keyword(s):  
Experimental Data ◽  
Flow Control ◽  
Numerical Simulations ◽  
Fuel Consumption ◽  
Aerodynamic Drag ◽  
Active Flow Control ◽  
Ground Vehicles ◽  
Ground Vehicle ◽  
Jet Actuators ◽  
Active Flow

In U.S, the ground vehicles consume about 77% of all (domestic and imported) petroleum; 34% is consumed by automobiles, 25% by light trucks and 18% by large heavy duty trucks and trailers. It has been estimated that 1% increase in fuel economy can save 245 million gallons of fuel/year. Additionally, the fuel consumption by ground vehicles accounts for over 30% of CO2 and other greenhouse gas (GHG) emissions. Moreover, most of the usable energy from the engine goes into overcoming the aerodynamic drag (53%) and rolling resistance (32%); only 9% is required for auxiliary equipment and 6% is used by the drive-train. 15% reduction in aerodynamic drag at highway speed of 55mph can result in about 5–7% in fuel saving. The goal of this paper is to demonstrate by numerical simulations that the active flow control (AFC) technology can be easily deployed /retrofitted to reduce the aerodynamic drag of ground vehicles by 15–20% at highway speed. For AFC, we employ a few oscillatory jet actuators (also known as synthetic jet actuators) at the rear face of the ground vehicle. These devices are easy to incorporate into the existing vehicles with very modest cost. The cost may come down significantly for a large volume — in hundreds of millions, especially for ground vehicles. Numerical simulations are performed using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations on solution adaptive structured grids in conjunction with a two-equation realizable k-ε turbulence model. The commercially available grid generator “GAMBIT” and the CFD solver “FLUENT” are employed in the simulations. Three generic ground vehicle configurations are considered in the simulations; the experimental data has been available for these configurations without and with AFC. The numerical simulations are in good agreement with the experimental data. These studies clearly demonstrate that the AFC techniques can be effectively employed to achieve significant reduction (10–15%) in aerodynamic drag of ground vehicles thereby reducing the fuel consumption by 5–7%.

Numerical Simulation of Unsteady Flow around Ahmed Body with Active Flow Control

2013 ◽  
Vol 275-277 ◽  
pp. 402-408
Author(s):  
Bing Xin Wang ◽  
Zhu Hui ◽  
Zhi Gang Yang
Keyword(s):  
Flow Control ◽  
Recirculation Zone ◽  
Active Flow Control ◽  
The Body ◽  
Slant Angle ◽  
Control Approach ◽  
Pressure Drag ◽  
Active Flow ◽  
Velocity Pressure ◽  
Ahmed Body

The numerical investigations presented in this paper deal with active flow control approach at the rear end of the Ahmed body model with the slant angle of 25°.Results of the velocity, pressure and vorticity field demonstrate the main reasons that cause the pressure drag. The influence of the spanwise and streamwise vortices rolling up from the slant and the edges on the recirculation zone behind the body is examined. A control slot is set on the separated line at the conjunction of the roof and the slant. Two different actuation concepts by blowing and suction steady jets through the slot lead to a drug increase of 5.61% and a drug reduction of 13.20% with the efficiency of 12.53% respectively.

scholarly journals Active Flow Control of a Pump-Induced Wall-Normal Vortex With Steady Blowing

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Qiong Liu ◽  
Byungjin An ◽  
Motohiko Nohmi ◽  
Masashi Obuchi ◽  
Kunihiko Taira
Keyword(s):  
Flow Control ◽  
Structural Damage ◽  
Active Flow Control ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Slip Boundary Condition ◽  
Control Technique ◽  
Control Approach ◽  
Slip Boundary ◽  
Active Flow

Abstract The emergence of a submerged vortex upstream of a pump can reduce pump intake efficiency and cause structural damage. In this study, we consider the use of active flow control with steady blowing to increase the pressure distribution within a single-phase pump-induced wall-normal vortex model, which is based on the Burgers vortex with a no-slip boundary condition prescribed along its symmetry plane. The goal of our control is to modify the vortex core velocity profile. These changes are sought to increase the core pressure such that detrimental effects on the pump are alleviated. Three-dimensional direct numerical simulations are performed to examine the dynamics of the vortex with the application of axial momentum injection at and around the root of the vortex. We find that the active flow control approach can effectively modify the wall-normal vortical structure and significantly increase the low-core pressure by up to 81% compared to that of the uncontrolled case. The result shows that the control setup is also effective when it is introduced in an off-centered manner. Compared to the unsteady blowing and suction-based actuation from our previous work (Liu, Q., An, B., Nohmi, M., Obuchi, M., and Taira, K., 2018, “Core-Pressure Alleviation for a Wall-Normal Vortex by Active Flow Control,” J. Fluid Mech., 853, p. R1.), the current steady control technique offers an effective and simple flow control setup that can support robust operations of pumps.

scholarly journals Some aspects of aerodynamic flow control using synthetic-jet actuation

2011 ◽  
Vol 369 (1940) ◽  
pp. 1476-1494 ◽  
Author(s):  
Ari Glezer
Keyword(s):  
Flow Control ◽  
Spatial Scales ◽  
Active Flow Control ◽  
Cross Flow ◽  
Synthetic Jet ◽  
Base Flow ◽  
Bluff Bodies ◽  
Actuation Frequency ◽  
Zero Net Mass Flux ◽  
Aerodynamic Flow Control

Aerodynamic flow control effected by interactions of surface-mounted synthetic (zero net mass flux) jet actuators with a local cross flow is reviewed. These jets are formed by the advection and interactions of trains of discrete vortical structures that are formed entirely from the fluid of the embedding flow system, and thus transfer momentum to the cross flow without net mass injection across the flow boundary. Traditional approaches to active flow control have focused, to a large extent, on control of separation on stalled aerofoils by means of quasi-steady actuation within two distinct regimes that are characterized by the actuation time scales. When the characteristic actuation period is commensurate with the time scale of the inherent instabilities of the base flow, the jets can effect significant quasi-steady global modifications on spatial scales that are one to two orders of magnitude larger than the scale of the jets. However, when the actuation frequency is sufficiently high to be decoupled from global instabilities of the base flow, changes in the aerodynamic forces are attained by leveraging the generation and regulation of ‘trapped’ vorticity concentrations near the surface to alter its aerodynamic shape. Some examples of the utility of this approach for aerodynamic flow control of separated flows on bluff bodies and fully attached flows on lifting surfaces are also discussed.

Active Flow Control over the Car

2011 ◽  
Vol 110-116 ◽  
pp. 2521-2528
Author(s):  
Deepesh Kumar Singh ◽  
Gautam Bandyopadhyay
Keyword(s):  
Flow Control ◽  
Aerodynamic Drag ◽  
Active Flow Control ◽  
Lift Coefficient ◽  
Boundary Layer Suction ◽  
Car Model ◽  
The Standard Model ◽  
Drag And Lift ◽  
Drag And Lift Coefficient ◽  
Active Flow

Active flow control methods are used to reduce the aerodynamic drag over a car model. Method of Boundary layer suction at the top rear and air injection at the back of the car are used as the active flow control tools to suppress the aerodynamic drag. The computational results obtained using the standard model for the car model are verified first against the practical results obtained by wind tunnel experimentation so as to obtain the range of turbulence. Then a parametric study on the effect of the drag and lift coefficient of the car with respect to the parameters governing the active flow control is done. The drag coefficient is reduced by 20.25% using this strategy with 19.4% increase in the lift coefficient.

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