An Experimental Study on the Influence of Vortex Generators on the Shock-Induced Boundary Layer Separation at M=1.4

2009 ◽  
Vol 76 (4) ◽  
Author(s):  
A. Zare Shahneh ◽  
F. Motallebi
Keyword(s):  
Boundary Layer ◽  
Total Pressure ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Layer Separation ◽  
Streamwise Location ◽  
Pressure Distributions ◽  
Pressure Profiles ◽  
Displacement Thickness ◽  
Result Analysis

The results of an investigation into the effects that sub-boundary layer vortex generators (SBVGs) have on reducing normal shock-induced turbulent boundary layer separation are presented. The freestream Mach number and Reynolds number were M=1.45 and R=15.9×106/m, respectively. Total pressure profiles, static pressure distributions, surface total pressure (Preston pressure) distributions, oil flow visualization, and Schlieren photographs were used in the result analysis. The effects of SBVG height and the location upstream of the shock were investigated. A novel tetrahedron shape SBVG with different lengths (30 mm and 60 mm) was used for these experiments. The effect of streamwise location of the longer SBVG on the interaction was also investigated. The location of the shock wave was controlled by an adjustable choke mechanism located downstream of the working section. The results show that an increase in the distance for the longer SBVG from 17.4δR to 25.5δR did not remove the separation entirely, but the shorter SBVG provided higher total pressure distribution within the boundary layer in the recovery region. This also provided a healthier boundary layer profile downstream of the interaction region with lower displacement thickness and shape factor.

Sub boundary-layer vortex generators for the control of shock induced separation

2006 ◽  
Vol 110 (1106) ◽  
pp. 215-226 ◽  
Author(s):  
G. S. Cohen ◽  
F. Motallebi
Keyword(s):  
Boundary Layer ◽  
Total Pressure ◽  
Static Pressure ◽  
Pressure Rise ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Pressure Recovery ◽  
Flow Visualisation ◽  
Pressure Distributions ◽  
Pressure Profiles

Abstract The results of an investigation into the effects that sub-boundary layer vortex generators (SBVGs) have on reducing normal shock-induced turbulent boundary-layer separation are presented. The freestream Mach number and Reynolds number were M = 1·45 and 15·9 × 106/m, respectively. Total pressure profiles, static pressure distributions, surface total pressure distributions, oil flow visualisation and Schlieren photographs were used in the results analysis. The effects of SBVG height, lateral spacing and location upstream of the shock were investigated. A novel curved shape SBVG was also evaluated and comparisons against the conventional flat vane type were made. The results show that in all but two cases, separation was completely eliminated. As expected, the largest SBVGs with height, h = 55%δ, provided the greatest pressure recovery and maximum mixing. However, the shock pressure rise was highest for this case. The experiments showed that the mid height SBVG array with the largest spacing provided similar results to the SBVG array with the largest height. Reducing the distance to shock to 10δ upstream also showed some improvement over the SBVG position of 18δ upstream. It was suggested that total elimination of the separated region may not be required to achieve a balance of improved static pressure recovery whilst minimising the pressure rise through the shock. The effect of curving the SBVGs provided an improved near wall mixing with an improved static and surface total pressure recovery downstream of the separation line. The optimum SBVG for the current flow conditions was found to be the curved vanes of h = 40%δ, with the largest spacing, located at 18δ upstream of the shock. Overall, it was apparent from the results that in comparison to larger vortex generators with a height comparable to δ, for SBVGs the parameters involved become more important in order to obtain the highest degree of mixing from a given SBVG configuration.

Influence of the height of the vortex generators in the control of shock-induced separation of the boundary layers

2008 ◽  
Vol 112 (1133) ◽  
pp. 415-420
Author(s):  
G. S. Cohen ◽  
F. Motallebi
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Total Pressure ◽  
Static Pressure ◽  
Pressure Rise ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Flow Visualisation ◽  
Near Surface ◽  
Pressure Distributions

Abstract Experiments have been conducted to assess the effects that sub-boundary-layer vortex generators (SBVGs) have on reducing normal shock-induced turbulent boundary-layer separation. The freestream Mach number and Reynolds number were M = 1·45 and 15·9 × 106/m, respectively. Detailed measurements of a fully developed, flat plate turbulent boundary layer were used in order to assess the performance of ten different SBVG configurations. The SBVG performance was assessed by comparing total pressure profiles measured upstream of separation and downstream of reattachment. Static pressure distributions, near surface total pressure distributions, oil flow visualisation and Schlieren photographs were also used. The effect of SBVG height was investigated. The results show the largest SBVGs with height, h = 55%δ, provided the greatest static pressure recovery and maximum mixing. However, the shock pressure rise (wave drag) was highest for this case.

Boundary Layer Separation Control on a Flat Plate With Adverse Pressure Gradients Using Vortex Generators

2006 ◽  
Author(s):  
Edward Canepa ◽  
Davide Lengani ◽  
Francesca Satta ◽  
Ennio Spano ◽  
Marina Ubaldi ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Flat Plate ◽  
Particle Image ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Separation Control ◽  
Pressure Gradients ◽  
Layer Separation ◽  
Image Velocimetry

The continuous tendency in modern aeroengine gas turbines towards reduction of blade count and ducts length may lead to aerodynamic loading increase beyond the limit of boundary layer separation. For this reason boundary layer separation control methods, up to now mostly employed in external aerodynamics, begin to be experimented in internal flows applications. The present paper reports the results of a detailed experimental study on low profile vortex generators used to control boundary layer separation on a large-scale flat plate with prescribed adverse pressure gradients. Inlet turbulent boundary layer conditions and pressure gradients are representative of aggressive turbine intermediate ducts. This activity is part of a joint European research program on Aggressive Intermediate Duct Aerodynamics (AIDA). The pressure gradients on the flat plate are generated by increasing the aperture angle of a movable wall opposite to the flat plate. To avoid separation on the movable wall, boundary layer suction is applied on it. Complementary measurements (surface static pressure distributions, surface flow visualizations by means of wall mounted tufts, instantaneous and time-averaged velocity fields in the meridional and cross-stream planes by means of Particle Image Velocimetry) have been used to survey the flow with and without vortex generators. Three different pressure gradients, which induce turbulent separation in absence of boundary layer control, were tested. Vortex generators height and location effects on separation reduction and pressure recovery increase were investigated. For the most effective VGs configurations detailed analyses of the flow field were performed, that demonstrate the effectiveness of this passive control device to control separation in diffusing ducts. Particle Image Velocimetry vector and vorticity plots illustrate the mechanisms by which the vortex generators transfer momentum towards the surface, re-energizing the near-wall flow and preserving the boundary layer from separation.

scholarly journals The Effect of Vortex Generators on Shock-Induced Boundary Layer Separation in a Transonic Convex-Corner Flow

Aerospace ◽  
2021 ◽  
Vol 8 (6) ◽  
pp. 157
Author(s):  
Kung-Ming Chung ◽  
Kao-Chun Su ◽  
Keh-Chin Chang
Keyword(s):  
Boundary Layer ◽  
Surface Pressure ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Streamwise Vorticity ◽  
Layer Separation ◽  
Convex Corner ◽  
Corner Flow ◽  
The Mean ◽  
Control Surfaces

Deflected control surfaces can be used as variable camber control in different flight conditions, and a convex corner resembles a simplified configuration for the upper surface. This experimental study determines the presence of passive vortex generators, VGs (counter-rotating vane type), on shock-induced boundary layer separation for transonic convex-corner flow. The mean surface pressure distributions in the presence of VGs for h/δ = 0.2 and 0.5 are similar to those for no flow control. If h/δ = 1.0 and 1.5, there is an increase in the amplitude of the mean surface pressure upstream of the corner’s apex, which corresponds to greater device drag and less downstream expansion. There is a decrease in peak pressure fluctuations as the value of h/δ increases, because there is a decrease in separation length and the frequency of shock oscillation. The effectiveness of VGs also depends on the freestream Mach number. For M = 0.89, there is an extension in the low-pressure region downstream of a convex corner, because there is greater convection and induced streamwise vorticity. VGs with h/δ ≤ 0.5 are preferred if deflected control surfaces are used to produce lift.

Turbulent boundary layer separation control and loss evaluation of low profile vortex generators

2011 ◽  
Vol 35 (8) ◽  
pp. 1505-1513 ◽  
Author(s):  
Davide Lengani ◽  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Francesco Bertini
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Separation Control ◽  
Layer Separation ◽  
Low Profile

The Effects of Freestream Turbulence on the Profile Boundary Layer and Losses in a Compressor Cascade

1984 ◽  
Author(s):  
R. L. Evans
Keyword(s):  
Boundary Layer ◽  
Pressure Loss ◽  
Total Pressure ◽  
Boundary Layer Separation ◽  
Skin Friction Coefficient ◽  
Total Pressure Loss ◽  
Freestream Turbulence ◽  
Compressor Cascade ◽  
Deviation Angle ◽  
Displacement Thickness

The turbulent profile boundary layer on a one-foot chord compressor cascade blade has been measured with varying levels of freestream turbulence. Increased levels of freestream turbulence were found to increase the fullness of the velocity profiles, with a consequent decrease in displacement thickness and an increase in the skin friction coefficient. A small increase in freestream turbulence causes the cascade total-pressure loss to increase initially, while at the higher turbulence levels boundary layer separation was delayed, resulting in a decrease in the total-pressure loss and deviation angle.

Boundary Layer Separation Control on an Inclined Plate Using Jet and Vortex Actuator

2013 ◽  
Author(s):  
Sertac Cadirci ◽  
Hasan Gunes
Keyword(s):  
Boundary Layer ◽  
Inclination Angle ◽  
Cross Flow ◽  
Boundary Layer Separation ◽  
Velocity Profiles ◽  
Computational Domain ◽  
Inclined Plate ◽  
Layer Separation ◽  
Displacement Thickness ◽  
Wide Gap

In this numerical study a Jet and Vortex Actuator (JaVA) system is implemented on an inclined plate (with an inclination angle 6°) to control the laminar boundary layer separation. JaVA is an active flow control device similar to the synthetic jets that transports momentum into the boundary layer and interacts with the boundary layer velocity profiles. The JaVA used in this study is a two-dimensional rectangular cavity with an actuating plate mounted on the opening which is placed asymmetrically. The plate moves up and down in vertical direction with a specified frequency. As the actuating plate is mounted asymmetrically on the cavity-opening, there are one narrow (wn) and one wide gap (ww) between the plate and the cavity. First JaVA in a cross-flow on an inclined plate (with inclination angle 6°) is modeled using a computational domain including a moving zone to mimic the vertical motion of the actuating plate. As plate moves up and down like a piston, JaVA-induced vortices emanate from the wide gap and are injected into the oncoming boundary layer. The calculations are carried out by a commercial finite-volume-based unsteady, laminar, incompressible Navier-Stokes solver. Time-averaged flow fields are calculated to extract boundary layer profiles from various downstream stations. For different oscillation frequencies (f = 1, 2, 3 and 4 Hz) time averaged boundary layers are compared to the non-actuated case (f = 0). The variations of the important boundary layer characteristics (displacement thickness, momentum thickness, shape factor) as well as friction coefficient are also investigated. It is observed that with increasing plate frequency or jet-Reynolds number (ReJ = 4abf/ν), JaVA-induced vortices interact with the cross-flow and modify the boundary layer characteristics. This has been shown in the time-averaged velocity profiles with a fuller shape causing larger displacement thicknesses and in association with them the shape factors drop and the friction coefficients increase. The proposed control method based on alternating suction and blowing with an oscillating plate is effective in delaying or preventing the flow separation downstream of an inclined plate.

Flow Control in an Aggressive Inter-Turbine Duct Using Low Profile Vortex Generators

2012 ◽  
Author(s):  
Yanfeng Zhang ◽  
Shuzhen Hu ◽  
Xue Feng Zhang ◽  
Michael Benner ◽  
Edward Vlasic
Keyword(s):  
Boundary Layer ◽  
Radial Pressure ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Flow Structures ◽  
Streamwise Vortices ◽  
Streamwise Vorticity ◽  
Layer Separation ◽  
Low Profile ◽  
Flow Mechanisms

This paper presents the experimental investigation of the flow in an aggressive inter-turbine duct (AITD). The goal is to improve the understanding of the flow mechanisms within the AITD and of the underlying physics of low-profile vortex generators (LPVGs). The flow structures in the AITD are dominated by counter-rotating vortices and boundary layer separations in both the casing and hub regions. At the first bend of the AITD, the casing boundary layer separates in a 3D mode because of the upstream wakes; this is followed by a massive 2D boundary layer separation. Due to the effect of the radial pressure gradient at the first bend, the streamwise vorticity generated by the casing 3D separation stays close to the casing endwall, and later mixes with the casing counter-rotating vortices formed at the second bend. By using LPVGs with different configurations installed on the casing, the casing boundary layer separation is significantly reduced. The streamwise vortices generated by the LPVGs have the potential to generate another pair of counter-rotating vortices at the AITD second bend, which help to delay/prevent the boundary layer separation. Therefore, the total pressure loss in the AITD was significantly reduced.

Detection of Boundary Layer Separation and Implementation of Autonomous Vortex Generators

2020 ◽  
Author(s):  
Samuel D. Morice ◽  
Kilian Ginnell ◽  
Shannon Geary ◽  
James Baughn ◽  
Stephen K. Robinson
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Layer Separation
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