Performance Margins of Non-Reflecting Slotted Walls in a Transonic Linear Cascade Tunnel

An experimental investigation was conducted into the endwall interference from a low-pressure turbine nozzle blade profile tested in linear cascade at an isentropic discharge Mach number of 1.27. This was above the profile design point of Mach 0.995. This highlighted that inviscid flow phenomena, at the cascade pitchwise boundaries, are the main cause of spurious end-wall interference at these test conditions. Specifically, fish-tail shocks from the profile trailing edges reflect at these boundaries disturbing the interior flow. An appreciable reduction of such interference was obtained through the use of a slotted tailboard downstream of the outmost blade trailing edge, with void ratio and pitch optimized to operate at Mach 1.27 in this cascade wind tunnel. Cascade tests in the Mach number range 1.20 to 1.32 show that the tailboard at off-design conditions gives a more pitchwise periodic discharge than without a tailboard and a test section open jet boundary. Reducing the tailboard pitch from its design value of 64° to 62° does not further improve the flow pitchwise periodicity over the Mach number range 1.18 to 1.31. Over this range, the slotted tailboard at its design pitch angle retains an appreciable performance margin over the other two end-wall configurations tested.