Influence of Mach number on the off-design performance of S-shaped compressor transition duct under the combined effect of curvature and pressure gradient

The compressor transition duct transfers the air from the low-pressure compressor to the high-pressure compressor. An aircraft always experiences off-design conditions except for level flight conditions during aircraft range. So, to throw some light on the performance of transition ducts under off-design conditions, this paper presents its performance assessment numerically for uniform and swirl flow cases under varying Mach numbers (M). This analysis reveals that a higher Mach number provokes an adverse pressure gradient and non-uniformity. In the uniform flow, the non-uniformity attains a maximum value of 0.04366 near the inner wall, which indicates the presence of a highly distorted flow near the inner wall; however, its maximum value is 0.03661 near to the outer wall in the swirl flow. Also, the pressure recovery reduces with an increased Mach number. Notably, as the Mach number increasesfrom the design point, the pressure coefficient along the convex curvature significantly drops to the lowest point of −0.65015 and −0.79324 for uniform and swirl flow, respectively. Consequently, the inner wall experiences a large adverse pressure gradient (−0.90822) compared to the decreasing Mach number from the design point for the uniform flow, whereas it is experienced by the outer wall in the case of swirl flow (−0.94729).