Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade

Abstract

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4%. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40% of chord. For high turbulence levels (Tu > 3%) and high Reynolds numbers transition propagates upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably and at Tu = 4% bypass transition is observed near 7–10% of chord. Experimental results are compared to theoretical predictions using the transition model which is implemented in the MISES code of Youngren and Drela. Overall the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.

Controlling Secondary Flows in Highly-Loaded Compressor Cascades

“…point of maximum velocity), as the Reynolds number was increased. Similar conclusions were obtained from the analytical studies performed on a compressor cascade by Schreiber et al (2002). The blade profile used had a design inlet Mach number of 0.6, a flow turning of 16° and a suction peak at 30% chord.…”

“…scale are 4% and 0.4B x for this grid (Mahallati, 2003). Different compressor cascades Inlet Flow at -1.2B x Outlet Flow at 1.6B x 6 6 7 7 8 8 (Küsters et al, 1999;Köller et al, 2000;Schreiber et al, 2002) and turbine cascades (Zoric, 2006;Gregory-Smith and Cleak, 1992) investigators studied the effects of freestream turbulence intensity on the secondary flows showed that it had little influence in the range of the Reynolds numbers experienced in the present study. Based on these investigations, it is assumed that the freestream turbulence intensity has little effect on the secondary flows in the present study.…”

Continuous Closed-Loop Transonic Linear Cascade for Aerothermal Performance Studies in Microturbomachinery

“…According to the profile loading distribution, the blades are subjected to an 8 kg force, yielding negligible torque and stress values. Figure 11 shows the vanes installed on the window using a set of vane mounts (1), self-lubricating bronze bearings (2,3,4), and an O-ring (5). Tolerances of the blademount interface are critical, as every 5 lm translates to 0.1 deg rotation of the vane trailing edge, resulting in a 1% change in throat area.…”

“…Addressing these issues, there are a limited number of continuous transonic turbine research rigs, capable of operating in various Reynolds conditions. Regardless of operational principle, a noninclusive list of existing transonic linear cascade facilities in academic institutions is provided in Table 1 [1][2][3][4][5][6][7][8][9][10][11][12]. The only heated test rigs among them are in Ecole Polytechnique Federal de Lausanne and Virginia Tech [2,11].…”

Investigation of Positively Curved Blade in Compressor Cascade Based on Transition Model

“…Nowadays, the need for load on compressor is increasing, which makes the reversed pressure gradient near the suction surface in the passage gradually increase, resulting in a significant rise of the three-dimensional character and the complexity of flow, and the development of the boundary layer separation and transition becomes more sensitive with external factors. Schreiber et al [4] studied the effect of Reynolds number and turbulence intensity on boundary layer transition using a surface flow visualization test method. They considered the position and geometric characteristics of the transition phenomenon and pointed out that it was necessary to pay attention to the characteristics of locations and geometry such as the starting location of transition and the width of laminar separation bubbles.…”