“…Their purpose is to control boundary layer separation due to adverse pressure gradients [1,2] and shock-induced separation [2,3]. They have also been used to reduce fluctuating pressure loads for buffet control [4,5]. VGs energize the boundary layer by enhancing mixing between the higher momentum external flow and the low momentum near-wall flow.…”
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 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: wedgeshaped 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.
Nomenclaturefreestream flow velocity, ms 1 u = local flow velocity, ms 1 X = streamwise coordinate, mm Y = vertical coordinate, mm Z = spanwise coordinate, mm = boundary layer thickness, mm = boundary layer displacement thickness, mm R 0 1 u= e U e dy = boundary layer momentum thickness, mm R 0 u= e U e 1 u= e U e dy Subscripts 0 = total conditions 1 = upstream of shock 1 = freestream
“…Their purpose is to control boundary layer separation due to adverse pressure gradients [1,2] and shock-induced separation [2,3]. They have also been used to reduce fluctuating pressure loads for buffet control [4,5]. VGs energize the boundary layer by enhancing mixing between the higher momentum external flow and the low momentum near-wall flow.…”
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 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: wedgeshaped 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.
Nomenclaturefreestream flow velocity, ms 1 u = local flow velocity, ms 1 X = streamwise coordinate, mm Y = vertical coordinate, mm Z = spanwise coordinate, mm = boundary layer thickness, mm = boundary layer displacement thickness, mm R 0 1 u= e U e dy = boundary layer momentum thickness, mm R 0 u= e U e 1 u= e U e dy Subscripts 0 = total conditions 1 = upstream of shock 1 = freestream
“…The increase in frequency may be due to the result of the reduction in the intermittent length ( L s ) for the constant shock velocity. 47 As discussed earlier, beyond the injection pressure of 208.5 kPa, there was no major variation in intermittent length, which is reflected as overlap in the spectral value at higher injection pressures. Figure 15.Spectral energy distribution for the flow control devices.…”
Section: Resultsmentioning
confidence: 65%
“…As the γ value increases, the fcis observed to increase indicating an increase in the shock jitter. Earlier studies have reported 47 that at γ≈0.5, the fc reaches the peak value and any further increase in γ shows a reduction in fc value. On careful observation, Figure 17, the as-symmetry in the fc curve can be seen as indicated by two lines at γ = 0.2 (fc = 0.3) and at γ = 0.8 (fc = 0.42).…”
Section: Resultsmentioning
confidence: 86%
“…The distance between the upstream and downstream boundary is usually defined as the intermittent region length, L s (0.1≤γ≤ 0.9). 47 For the current incident angle 22°, the L s was calculated to be around 10.75 mm or 1.68δ. Figure 9.Intermittency value distribution with various flow control devices.…”
Section: Resultsmentioning
confidence: 99%
“…In order to get an idea about the number of times on an average the separation shock passes through a given transducer location in a given direction, the parameter widely used is zero-crossing frequency. 47 The conditional sampling technique was again used to generate the box-car signal as shown in Figure 16. The time interval ( T m ) between two shock waves to pass a given transducer location can be determined by where, N is number of periods and Tm is the mean value.…”
Experiments were carried out to control an incident shock-induced separation associated with 22° shock generator in a Mach 3.5 flow using an array of steady micro-jet actuators. Four micro-jet actuator configurations based on the variation in their pitch angle [Formula: see text], skew angle [Formula: see text] and span-wise spacing were used. Each of these configurations were placed 14 δ upstream of the interaction and operated with injection pressures ( Poj) varying from 140 to 643 kPa. While no major variations in separation characteristics were observed for Poj < 140 kPa, significant modifications were observed beyond [Formula: see text] of 140 kPa and until 208.5 kPa. Amongst all the four control configurations, micro-jet vortex generator 2 ([Formula: see text] showed the best control with a 2 δ downstream shift in separation point location relative to no-control. The shift is also accompanied with a change in maximum zero-crossing frequency towards higher frequency (almost twice), a reduction in the intermittency length and an increase in the correlation value between the boundary layer just upstream of the interaction and the intermittent region. These results indicate that the effectiveness of micro-jet vortex generator 2 is probably due to the improved entrainment levels in the shear layer induced by the micro-vortices which are generated downstream of these devices. The increase of the skew angle [Formula: see text] from 180° to 270° for the same pitch angle of β = 45° (micro-jet vortex generator 3) seems to have no major impact on the separation characteristics. The reduction in the span-wise spacing (micro-jet vortex generator 4) resulted in deterioration of the flow field due to the jet-to-jet interaction with increasing injection pressures.
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