Sub-boundary Layer Vortex Generators Research Articles

Testing the Accuracy of the Cell-Set Model Applied on Vane-Type Sub-Boundary Layer Vortex Generators

Vortex Generators (VGs) are applied before the expected region of separation of the boundary layer in order to delay or remove the flow separation. Although their height is usually similar to that of the boundary layer, in some applications, lower VGs are used, Sub-Boundary Layer Vortex Generators (SBVGs), since this reduces the drag coefficient. Numerical simulations of sub-boundary layer vane-type vortex generators on a flat plate in a negligible pressure gradient flow were conducted using the fully resolved mesh model and the cell-set model, with the aim on assessing the accuracy of the cell-set model with Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) turbulence modelling techniques. The implementation of the cell-set model has supposed savings of the 40% in terms of computational time. The vortexes generated on the wake behind the VG; vortical structure of the primary vortex; and its path, size, strength, and produced wall shear stress have been studied. The results show good agreements between meshing models in the higher VGs, but slight discrepancies on the lower ones. These disparities are more pronounced with LES. Further study of the cell-set model is proposed, since its implementation entails great computational time and resources savings.

The Wingtip Vortex of a Dimpled Wing With an Endplate

Dimples used as sub-boundary layer vortex generators have been shown to reduce wake size at large angles of incidence. The effect these dimples have on wingtip vortices with an endplate is measured via laser Doppler anemometry (LDA) on an inverted Tyrrell026 airfoil (ReC = 0.5 × 105 and chord = 0.075 m) in ground effect in order to determine the flow characteristics for this configuration and to see if previous measurements were performed in a thinner part of the wake due to any potential wake waviness. The strength of the wingtip vortex for the dimpled wing is 10% higher than the “clean” wing immediately downstream. The clean wing has large region of high turbulence throughout the wake, and the dimples reduce this by 50%. The net result is that dimples drastically improve the flow in the wake of the wing and endplate.

Computational Investigation of a Race Car Wing With Vortex Generators in Ground Effect

Vortex generators can be applied to control separation in flows with adverse pressure gradients, such as wings. In this paper, a study using three-dimensional steady computations for an inverted wing with vortex generators in ground effect is described. The main aim is to provide understanding of the flow physics of the vortex generators, and how they affect the overall aerodynamic performance of the wing to complement previous experimental studies of the same configuration. Rectangular vane type sub-boundary layer and large-scale vortex generators are attached to the suction surface of the wing, including both counter-rotating and co-rotating configurations. In order to provide confidence, Reynolds-averaged Navier–Stokes simulations using the Spalart–Allmaras turbulence model are validated against the experimental results regarding force, pressure, and wake characteristics, with the validation exhibiting close agreement with the experimental results. The streamwise friction shows the downwash induced by the generated vortex acts to suppress flow separation. The flow field survey downstream of the vortex generators features breakdown and dominance of the generated vortex in the flow. The vortex generated by the counter-rotating sub-boundary layer vortex generator grows in size and breaks down as it develops downstream, while the vortex generated by the counter-rotating large-scale vortex generator shows high vorticity even further downstream, indicating the persistence of the vortex in the flow. The flow field behind the co-rotating sub-boundary layer vortex generator is dominated by a lateral flow, having the spanwise flow component rather than a swirling flow, and the vortex quickly dissipating as it develops downstream. The results from this paper complement previous experimental measurements by highlighting the flow physics of how vortex generators can help control flow separation for an inverted wing in ground effect, and how critical vortex generator type and size are for its effectiveness.

Flow Physics of a Race Car Wing With Vortex Generators in Ground Effect

This paper experimentally investigates the use of vortex generators for separation control on an inverted wing in ground effect using off-surface flow measurements and surface flow visualization. A typical racing car wing geometry is tested in a rolling road wind tunnel over a wide range of incidences and ride heights. Rectangular vane type of sub-boundary layer and large-scale vortex generators are attached to the suction surface, comprising counter-rotating and corotating configurations. The effects of both device height and spacing are examined. The counter-rotating sub-boundary layer vortex generators and counter-rotating large-scale vortex generators suppress the flow separation at the center of each device pair, while the counter-rotating large-scale vortex generators induce horseshoe vortices between each device where the flow is separated. The corotating sub-boundary layer vortex generators tested here show little evidence of separation control. Increasing the spacing of the counter-rotating sublayer vortex generator induces significant horseshoe vortices, comparable to those seen in the counter-rotating large-scale vortex generator case. Wake surveys show significant spanwise variance behind the wing equipped with the counter-rotating large-scale vortex generators, while the counter-rotating sub-boundary layer vortex generator configuration shows a relatively small variance in the spanwise direction. The flow characteristics revealed here suggest that counter-rotating sub-boundary layer vortex generators can provide effective separation control for race car wings in ground effect.

Flow Separation Control on a Race Car Wing With Vortex Generators in Ground Effect

Flow separation control using vortex generators on an inverted wing in ground effect is experimentally investigated, and its performance is characterized in terms of forces and pressure distributions over a range of incidence and ride height. Counter-rotating and co-rotating rectangular-vane type vortex generators are tested on the suction surface of the wing. The effect of device height and spacing is investigated. The counter-rotating sub-boundary layer vortex generators and counter-rotating large-scale vortex generators on the wing deliver 23% and 10% improvements in the maximum downforce, respectively, compared with the clean wing, at an incidence of one degree, and delay the onset of the downforce reduction phenomenon. The counter-rotating sub-boundary layer vortex generators exhibit up to 26% improvement in downforce and 10% improvement in aerodynamic efficiency at low ride heights. Chordwise pressure measurement confirms that both counter-rotating vortex generator configurations suppress flow separation, while the co-rotating vortex generators exhibit negligible effectiveness. This work shows that a use of vortex generators, notably of the counter-rotating sub-boundary layer vortex generator type, can be effective at controlling flow separation, with a resultant improvement in downforce for relatively low drag penalty.

Effects of micro-ramps on a shock wave/turbulent boundary layer interaction

Stereoscopic particle image velocimetry is used to investigate the effects of micro-ramp sub-boundary layer vortex generators, on an incident shock wave/boundary layer interaction at Mach 1.84. Single- and double-row arrangements of micro-ramps are considered. The micro-ramps have a height of 20% of the unperturbed boundary layer thickness and the measurement planes are located 0.1 and 0.6 boundary layer thicknesses from the wall. The micro-ramps generate packets of individual vortex pairs downstream of their vertices, which produce counter-rotating longitudinal streamwise vortex pairs in a time-averaged view. These structures induce a pronounced spanwise variation of the flow properties, namely the mixing across the boundary layer interface. The probability of reversed-flow occurrence is decreased by 20 and 30% for the single- and double-row configurations, respectively. Both configurations of micro-ramps stabilize the shock motion by reducing the length of its motion by about 20% in the lower measurement plane. The results are summarized by a conceptual model describing the boundary layer’s and interaction’s flow pattern under the effect of the micro-ramps.

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

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.

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

AbstractExperiments 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.

Effect of Microvortex Generators On Seperated Normal Shock/ Boundary Layer Interactions

Experiments have been performed in a blowdown supersonic wind tunnel to investigate the effect of subboundary layer vortex generators placed upstream of a normal shock/turbulent boundary layer interaction at a Mach number of 1.5 and a freestream Reynolds number of 28 x 10 6 . The Reynolds number based on the inflow boundary layer displacement thickness was 26,000. Two types of subboundary layer vortex generators were investigated: wedge-shaped and counter-rotating vanes. It was found that the vane-type subboundary layer vortex generators eliminated and the wedge-type subboundary layer vortex generators greatly reduced the shock-induced separation. When placed in the supersonic part of the flow, both types of subboundary layer vortex generators caused a wave pattern consisting of a shock, reexpansion, and shock. The reexpansion and double shocks are undesirable features because they equate to increased total pressure losses. Furthermore there are indications that the vortex intensity is reduced by the normal shock/boundary layer interaction. Overall, the vane-type subboundary layer vortex generators were the more effective devices as they eliminated the shock-induced separation and had the least detrimental effect on the shock structure.

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

AbstractThe 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 ofh= 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.