Abstract: To investigate the effect of wake/shock on downstream turbine blade aerodynamic load distribution in multistage vaneless counter-rotating turbine, this paper employed unsteady numerical simulation to analyze the influence of complex inter-stage flow on the pressure fluctuation on the downstream blade surface. The absence of guide vanes in multistage vaneless counter-rotating turbine creates uncovered suction side of the first-stage moving blade, form-ing a converging-diverging wake flow passage resembling a Laval nozzle. Unsteady rotor/rotor interactions de-crease the outlet Mach number of the first-stage moving blade, forming a new compression wave (wake flow pas-sage shock) near its trailing edge. Since the propagation direction of the wake flow passage shock is the same as the rotation direction of the first-stage moving blade, within one cycle, the wake flow passage shock only sweeps across the suction side of the second-stage moving blade. Reflected shock of pressure side leg of the trailing edge shock sweeps from the suction side to the pressure side of the second-stage moving blade, and its velocity is faster than that of the wake flow passage shock. At a specific moment within one cycle, reflected shock of pressure side leg of the trailing edge shock and the wake flow passage shock wave act simultaneously on the 28.8% axial posi-tion of the suction side of the second-stage moving blade, causing a significant increase in the pressure fluctuation peak at that position, with the peak reaching 81.2% of that caused by suction side leg of the trailing-edge shock sweep-induced pressure fluctuation peak. Suction side leg of the trailing-edge shock is the primary factor causing changes in the pressure load on the blade surface of the second-stage moving blade, with its main disturbance re-gion being the leading edge of the second-stage moving blade. The maximum pressure fluctuation peak caused by suction side leg of the trailing-edge shock sweep in this region within one cycle reaches 47.7% of the pressure mean value. Due to the dissipative effect of reflected shock of pressure side leg of the trailing edge shock and wake flow passage shock waves, the wake intensity of the first-stage moving blade decreases significantly, resulting in a minor influence on the aerodynamic load on the blade surface of the second-stage moving blade. Spectral analysis results indicate that due to the superimposed effect of the wake flow passage shock wave and reflected shock of pressure side leg of the trailing edge shock, similar to the suction side leg of the trailing-edge shock, the main fre-quency of the pressure fluctuation on the blade surface of the second-stage moving blade is twice the sweep fre-quency of the suction side leg of the trailing-edge shock.

Key words: counter-rotating turbine, numerical simulation, rotor/rotor interactions, unsteady flow, aerodynamic load