Experimental Flow Visualization Study of Flow Separation Control With High-Frequency Translational Surface Actuation

2020 ◽  
Author(s):  
Kenechukwu Okoye ◽  
Wing Lai ◽  
Taiho Yeom
Keyword(s):  
Flow Separation ◽  
High Frequency ◽  
High Speed ◽  
Free Stream ◽  
Separation Bubble ◽  
Angle Of Attack ◽  
Small Displacement ◽  
Peak Displacement ◽  
Flow Separation Control ◽  
Translational Surface

Abstract Flow separation causes aircraft to experience an increase in drag degrading their aviation performance. The current study aims to delay flow separation on an airfoil by embedding a high-frequency translational piezoelectric actuator along the surface of the airfoil. The actuators with two actuation surfaces were embedded on the suction surface of an Eppler 862 airfoil model and placed in a low-speed wind tunnel. Consecutive pictures of the flow fields with dry ice fogs around the airfoil were taken using a high speed camera in order to observe the flow separation phenomenon before and after turning on the high-frequency translational surface actuation. The effects of the actuation on the flow separation were observed at various actuation displacements, angles of attack, and free stream velocities. The operating frequency of the surface actuation was 565 Hz. The measured actuation mean-to-peak displacement ranged up to 0.12 mm at the maximum applied voltage of 150 V. The angle of attack of the airfoil varied from 6° to 24°. The chord Reynolds number was increased up to around 262,000. It was confirmed that the actuation had a very strong influence on the flow separation even at a very small displacement of 0.024 mm remaining significantly reduced separation bubble compared to the one before activating the actuators at 4.3 m/s of velocity and 14° of angle of attack. The flow separation was completely suppressed when the actuation displacement reached around 0.082 mm under the same conditions of flow velocity and angle of attack. This implied that the actuation should generate a strong enough momentum relative to the free stream in order to completely suppress the flow separation. In summary, the study confirmed that the employed high-frequency translational surface actuation had the obvious control authority on delaying or suppressing the flow separation over the airfoil depending on the parameters changed.

Preliminary Experimental Study on Closed-loop Flow Separation Control Utilizing Deep Q-Network over Fixed Angle-of-Attack Airfoil

2018 ◽  
Author(s):  
Satoshi Shimomura ◽  
Satoshi Sekimoto ◽  
Hiroaki Fukumoto ◽  
Akira Oyama ◽  
Kozo Fujii ◽  
...  
Keyword(s):  
Experimental Study ◽  
Flow Separation ◽  
Closed Loop ◽  
Angle Of Attack ◽  
Separation Control ◽  
Flow Separation Control ◽  
Fixed Angle

Flow separation control of NACA-2412 airfoil with bio-inspired nose

2019 ◽  
Vol 91 (7) ◽  
pp. 1058-1066 ◽  
Author(s):  
Mohamed Arif Raj Mohamed ◽  
Ugur Guven ◽  
Rajesh Yadav
Keyword(s):  
Flow Control ◽  
Flow Separation ◽  
Control Method ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Separation Control ◽  
Cetacean Species ◽  
Aerodynamic Efficiency ◽  
Content Type ◽  
Flow Separation Control

Purpose The purpose of this paper is to achieve an optimum flow separation control over the airfoil using passive flow control method by introducing bio-inspired nose near the leading edge of the NACA 2412 airfoil. Design/methodology/approach Two distinguished methods have been implemented on the leading edge of the airfoil: forward facing step, which induces multiple accelerations at low angle of attack, and cavity/backward facing step, which creates recirculating region (axial vortices) at high angle of attack. Findings The porpoise airfoil (optimum bio-inspired nose airfoil) delays the flow separation and improves the aerodynamic efficiency by increasing the lift and decreasing the parasitic drag. The maximum increase in aerodynamic efficiency is 22.4 per cent, with an average increase of 8.6 per cent at all angles of attack. Research limitations/implications The computational analysis has been done for NACA 2412 airfoil at low subsonic speed. Practical implications This design improves the aerodynamic performance and increases structural strength of the aircraft wing compared to other conventional high-lift devices and flow-control devices. Originality/value Different bio-inspired nose designs which are inspired by the cetacean species have been analysed for NACA 2412 airfoil, and optimum nose design (porpoise airfoil) has been found.

Experimental Study on Closed-loop Flow Separation Control Utilizing Deep Q-Network over Fixed Angle-of-Attack Airfoil

2018 ◽  
Vol 2018 (0) ◽  
pp. S0520306
Author(s):  
Satoshi SHIMOMURA ◽  
Satoshi SEKIMOTO ◽  
Hiroaki HUKUMOTO ◽  
Akira OYAMA ◽  
Kozo FUJII ◽  
...  
Keyword(s):  
Experimental Study ◽  
Flow Separation ◽  
Closed Loop ◽  
Angle Of Attack ◽  
Separation Control ◽  
Flow Separation Control ◽  
Fixed Angle

Shock–Boundary Layer-Interaction Control Through Recirculation in a Hypersonic Inlet

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Alex Ruban ◽  
Viren Menezes ◽  
Sridhar Balasubramanian ◽  
K. Srinivasan
Keyword(s):  
Boundary Layer ◽  
Flow Separation ◽  
High Speed ◽  
Separation Bubble ◽  
Control Flow ◽  
Test Model ◽  
Shock Train ◽  
Layer Interaction ◽  
Separation Shock ◽  
Boundary Layer Interaction

Abstract This technical brief presents a flow separation mitigation device, called cavity-recirculator that can be used to control flow separation during shock wave–boundary layer interaction (SBLI) in high-speed intake flows. The cavity-recirculator isolates the flow separation bubble generated at the SBLI spot, thereby thinning the boundary layer and reducing the blockage of the inviscid stream in the duct. The device has a potential application in scramjet engine intakes/isolators. The cavity-recirculator was tested on a single-ramp-compression intake model in a hypersonic shock tunnel, in a freestream of Mach 8 (±0.1). The device operation and effectiveness were assessed by flow visualization and pressure measurements in the test model. The measurements and visualization displayed a mitigation of flow separation through an improved flow field with a single shock train and the absence of flow separation shock, in the inlet.

Effects of free-stream turbulence on surface pressure fluctuations in a separation bubble

1997 ◽  
Vol 337 ◽  
pp. 1-24 ◽  
Author(s):  
P. J. SAATHOFF ◽  
W. H. MELBOURNE
Keyword(s):  
Shear Layer ◽  
High Speed ◽  
Free Stream ◽  
Separation Bubble ◽  
Longitudinal Velocity ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Turbulence Scale ◽  
Free Stream Turbulence ◽  
Large Pressure

Wind-tunnel experiments were conducted to investigate the cause of large pressure fluctuations near leading edges of sharp-edged bluff bodies. Measurements obtained with a blunt flat plate showed that very low pressures occur in a narrow region located approximately 0.25XR from the leading edge, where XR defines the distance from the leading edge to the mean reattachment location. This phenomenon occurs in the undisturbed flow as well as turbulent flow, although the magnitude of peak pressure fluctuations increases with both turbulence intensity, σu/u, and turbulence scale, LX.Flow visualization experiments conducted with a high-speed cine-camera reveal the process that causes large pressure fluctuations in separation bubbles. This process is initiated when a perturbation in the approaching flow causes a roll-up of the separated shear layer, producing a strong vortex near the surface. Conditional sampling of pressure data was used to determine the spanwise length of the vortex. A significant increase in the spanwise correlation of pressure fluctuations occurs when the shear layer rolls up. Coherence measurements indicate that the spanwise length of vortices in the separation bubble is not directly related to longitudinal velocity fluctuations in the free-stream.

Numerical Investigation of Three-dimensional Separation Control on a High-speed Compressor Stator Vane with Tailored Synthetic Jet

2020 ◽  
Vol 37 (4) ◽  
pp. 383-397 ◽  
Author(s):  
Yong Qin ◽  
Yanping Song ◽  
Ruoyu Wang ◽  
Huaping Liu
Keyword(s):  
Flow Control ◽  
Flow Separation ◽  
High Speed ◽  
Numerical Study ◽  
Three Dimensional ◽  
Synthetic Jet ◽  
Separation Control ◽  
Flow Separation Control ◽  
Control Efficiency ◽  
Stator Vane

AbstractA numerical study on the performance of synthetic jet for flow separation control on a high-speed compressor stator vane is performed. Four control schemes including full-span and part-span configurations are investigated at both design and off-design conditions. Results indicate that both full-span and part-span schemes could effectively delay flow separation and reduce total pressure loss for the compressor stator vane, the adaptability of the flow control under off-design conditions is also validated. Within the investigated incidence range, the full-span configuration is able to gain the most significant performance improvement, by which a maximum loss reduction of 23.8 % is obtained at i=2 deg. The part-span configuration could reorganize the vortex structures more efficiently and cut off the interaction between the ring-like vortex and the passage vortex, thus improving its performance in the corner region. In terms of flow control efficiency, the part-span configurations turn out to be more superior, where the highest control efficiency of 614.0 % is achieved at i=0 deg with the total height of the actuator being 40 %H. The flow control efficiency for all the schemes is higher than 100 % within the whole operating range, demonstrating a promising prospect for the application of synthetic jet in axial compressors.

Investigation of a Separated Boundary Layer and its Influence on Secondary Flow of a Transonic Turbine Profile

2014 ◽  
Author(s):  
Roland E. Brachmanski ◽  
Reinhard Niehuis ◽  
Arianna Bosco
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Turbine Blade ◽  
Flow Separation ◽  
High Speed ◽  
Separation Bubble ◽  
Armed Forces ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Operation Conditions

Profile losses of the turbine blade and secondary flow losses are the main source of aerodynamic loss in a low pressure turbine. However, not much attention has been paid in the interaction between these two loss sources. This paper investigates the interaction mechanisms between a separated boundary layer on the suction side and the secondary flow in blade passages. The high speed cascade wind tunnel of the University of the Federal Armed Forces Germany has been used to achieve the required operation conditions, generating a flow separation on the suction side. The profile of this cascade has been chosen due to the flow separation behavior on the suction side of the blade at low Reynolds numbers. Different measurements techniques are conducted to further investigate the effects seen in CFD. The aim of this paper is to investigate the interaction phenomena between the secondary flow and a separation bubble at different Reynolds numbers. The development and change of the boundary layer in the axial and radial directions on the suction side of the turbine blade are presented and discussed. The results show discrepancies between the numerical prediction and the experimental data on the suction side of the blade rise as the effects of the secondary flow increase. Furthermore, the increasing influence of the radial pressure gradient of the secondary flow leads to a noticeable reduction in the length of the separation bubble close to the endwall region.

Experimental Investigations of Laminar Separation Bubble for a Flow Past an Airfoil

2010 ◽  
Author(s):  
Deepakkumar M. Sharma ◽  
Kamal Poddar
Keyword(s):  
Boundary Layer ◽  
Flow Separation ◽  
Separation Bubble ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Experimental Investigations ◽  
Stream Velocity ◽  
Laminar Separation Bubble ◽  
Laminar Separation

Wind tunnel experiments were carried out on NACA 0015 airfoil model to investigate the formation of laminar separation bubble on the upper surface of the airfoil by varying angle of attack from −5° to 25° with respect to the free stream velocity at constant Reynolds number varying from 0.2E06 to 0.6E06. Pressure signals were acquired from the pressure ports selected at the mid-span of the airfoil model along the chord. Static stall characteristics were obtained from the surface pressure distribution. The flow separation was found to be a trailing edge turbulent boundary layer separation preceded with a laminar separation bubble. Flow Visualizations were done by using Surface Oil flow Technique for qualitative analysis of the transition zone formed due to the presence of laminar separation bubble As the angle of attack is increased the separation bubble moves towards the leading edge of the airfoil and finally gets shredded or burst at a particular angle of attack resulting in leading edge turbulent flow separation which induces the static stall condition. The flow separation process is critically analyzed and the existence of laminar separation bubble is visualized and quantified with the increase in angle of attack and Re. Effect of Re and angle of attack on the various boundary layer and Separation bubble parameters are obtained and analyzed.

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