Design of Two Counter-Rotating Fan Types and CFD Investigation of Their Aerodynamic Characteristics

Abstract

The design information and numerical investigation are presented for two kinds of counter-rotating fans. The fans, both vaneless and non-aspirated, are intended for a civil aviation engine with a bypass ratio of 8 and for a military engine with a bypass ratio of 0.5 respectively. The pressure ratios are respectively 1.60 and 3.50, and the tip speeds are (300 m/s, −222 m/s) and (500 m/s, −391 m/s). The design rotating speed ratio of the front to the aft rotor is discussed based on one-dimensional analysis. The variations in pressure ratios, isentropic efficiencies, diffusion losses and shock losses at mean-line with the design rotating speed ratios are studied. The flow fields of the two contra-stages are numerically simulated and the detailed flow physics is investigated at both design and off-design conditions. The simulations reveal that the two stages both perform well. The civil engine contra-stage test fans are still conventional transonic rotors due to the low pressure ratio and low tip speeds. For the military engine contra-stage, the aft rotor differs from the conventional transonic front rotor. It is a full-span relative supersonic rotor in which both the leading edge shock and the passage shock extend from the casing to the hub. At the stall point, for the low pressure ratio civil test fan, both the front and aft rotors are stalled and the shocks detached. In the corresponding high pressure ratio military fan, only the aft rotor is stalled which determines the stage stall point.