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.

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.

scholarly journals Micro-Vortex Generators on Transonic Convex-Corner Flow

Aerospace ◽  
2021 ◽  
Vol 8 (9) ◽  
pp. 268
Author(s):  
Kung-Ming Chung ◽  
Kao-Chun Su ◽  
Keh-Chin Chang
Keyword(s):  
Boundary Layer ◽  
Pressure Fluctuations ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Convex Corner ◽  
Pressure Distributions ◽  
Corner Flow ◽  
Favorable Pressure Gradient ◽  
Oil Flow ◽  
Shock Oscillation

A convex corner models the upper surface of a deflected flap and shock-induced boundary layer separation occurs at transonic speeds. This study uses micro-vortex generators (MVGs) for flow control. An array of MVGs (counter-rotating vane type, ramp type and co-rotating vane type) with a height of 20% of the thickness of the incoming boundary layer is installed upstream of a convex corner. The surface pressure distributions are similar regardless of the presence of MVGs. They show mild upstream expansion, a strong favorable pressure gradient near the corner’s apex and downstream compression. A corrugated surface oil flow pattern is observed in the presence of MVGs and there is an onset of compression moving downstream. The counter-rotating vane type MVGs produce a greater reduction in peak pressure fluctuations and the ramp type decreases the separation length. The presence of MVGs stabilizes the shock and shock oscillation is damped.

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.

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

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.

Instantaneous Behavior of Streamwise Vortices for Turbulent Boundary Layer Separation Control

2006 ◽  
Vol 129 (2) ◽  
pp. 226-235 ◽  
Author(s):  
K. P. Angele ◽  
F. Grewe
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Separation Bubble ◽  
Vortex Generator ◽  
Boundary Layer Separation ◽  
Separation Control ◽  
Streamwise Vortices ◽  
Layer Separation ◽  
Vortex Size ◽  
The Mean

The present study investigates turbulent boundary layer separation control by means of streamwise vortices with focus on the instantaneous vortex behavior. A turbulent boundary layer is exposed to a pressure gradient that generates a separation bubble with substantial backflow. The separation bubble is controlled by conventional passive vortex generators creating pairs of counterrotating vortices. Quantitative information is achieved by applying Particle Image Velocimetry (PIV) to the cross-stream plane of the vortices. The characteristics of a pair of counter-rotating vortices shed from a vortex generator is investigated in the near-field downstream of the vortex generator. The vortices were found to grow with the boundary layer in the downstream direction, and the maximum vorticity decreases as the circulation is conserved. The vortices are nonstationary, and the movements in the spanwise direction are larger than those in the wall-normal direction, due to the presence of the wall. The vortices fluctuate substantially and move over a spanwise distance, which is approximately equal to their size. The most probable instantaneous separation between the two vortices shed from one vortex generator equals the difference between their mean positions. The unsteadiness of the vortices contributes to the observed maxima in the Reynolds stresses around the mean vortex centers. The instantaneous vortex size and the instantaneous maximum vorticity are also fluctuating properties, and the instantaneous vortex is generally smaller and stronger than the mean vortex. A correlation was found between a large instantaneous vortex size and a low instantaneous maximum vorticity (and vice versa), suggesting that the vortices are subjected to vortex stretching.

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

A Simple Means of Measuring Vortex Strength, and the Performance of Triangular Ramp-Type Vortex Generators in a Uniform Velocity Field

1962 ◽  
Vol 66 (624) ◽  
pp. 783-785
Author(s):  
A. D. McEwan ◽  
P. N. Joubert
Keyword(s):  
Boundary Layer ◽  
Velocity Field ◽  
Adverse Pressure Gradient ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Measuring Device ◽  
Vortex Strength ◽  
Layer Separation ◽  
Uniform Velocity ◽  
Edge Separation

The performance of triangular ramp vortex generators of a type used for boundary layer separation control, has been compared with that of equivalent wing or vane type of lifting generators, in a uniform velocity field, and was shown to be substantially inferior. Performance was established using a novel vortex strength measuring device of unusual simplicity, for which calibrations are given and applications are discussed.The usefulness of vortex generators in avoiding boundary layer separation due to an adverse pressure gradient has been established. Little, however, is known of the nature of vortex modified boundary layers. As part of an investigation into convective heat transfer through such layers it was desired to compare the circulation-drag performance of two representative generator configuration types, these being the popularly used stub wing or vane type, and the edge separation, plough or wedge type.

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