Endwall Contouring and Fillet Design for Reducing Losses and Homogenizing the Outflow of a Compressor Cascade

Abstract

The following paper deals with the development of an optimized fillet and an endwall contour for reducing the total pressure loss and for homogenizing the outflow of a highly loaded cascade with a low aspect ratio. The NACA-65 K48 cascade profile without a fillet and without endwall contouring is used as a basis. Optimizations are performed using the DLR in-house tool AutoOpti and the RANS-solver TRACE. Three operating points at an inflow Mach number of 0.67 with different inflow angles are used to secure a wide operating range of the optimized design. At first only a fillet is optimized. The optimized fillet is small at the leading edge and rather high, wide and thick towards the trailing edge. It reduces the total pressure loss and homogenizes the outflow up to a blade height of 20 %. Following this a combined optimization of the endwall and the fillet is performed. The optimized contour leads to the development of a vortex, which changes the secondary flow in such a way, that the corner separation is reduced, which in turn significantly reduces the total pressure loss up to 16 % in the design operating point. The contour in the outflow region leads to a significant homogenization of the outflow in the near wall region.

Advanced Endwall Contouring for Loss Reduction and Outflow Homogenization for an Optimized Compressor Cascade

“…The operating points were the same ones as in Reutter et al [13], being at OP0 44 • , OP1 38 • , and OP2 52 • . Thus, in contrast to the airfoil MISES optimization, where the OP2 is chosen at 51 • for the endwall optimization, the OP2 is chosen at 52 • due to the larger operating range of the full cascade compared to the airfoil 2D midsection.…”

“…While Reutter et al [13] used a NACA 65 K48 airfoil (National Advisory Committee for Aeornautics) as a base configuration for EWC in a cascade, this study uses an optimized airfoil. It is the next step in the DLR research on endwall contouring.…”

“…The endwall optimization is used not only in order to reduce the losses, but also to homogenize the exit flow angle for beneficial effects on a hypothetical next stage or on the combustion chamber. No 3D design of the blade was used in order to be better comparable to the former study [13], as well as to separate the relevant effects. Even using a 3D design would not have suppressed all of the secondary flow and influencing this is the main study focus and the main effect of EWC.…”

“…As future experiments are now planned for the transonic cascade wind tunnel (TGK) at DLR Cologne, in contrast to the work of Hergt [23] the profiles now have a chord length of 70 mm. In the study by Reutter et al [13] the numerical operating point at 44° inflow angle showed the lowest loss, so in this study the same operating point was chosen as the design point and called operating point 0 (OP0). The operating range, shown in Figure 2, is the operating range defined by the almost linear range of the static pressure ratio versus the inflow angle.…”

“…The endwall optimization was carried out similar to Reutter et al [13], but the optimized airfoil DLR SC14-067A (DLR) was used instead of NACA. The operating points were the same ones as in Reutter et al [13], being at OP0 44 • , OP1 38 • , and OP2 52 • .…”