Effect of variation in axial spacing and rotor speed combinations on the performance of a high aspect ratio contra-rotating axial fan stage

Abstract

This article reports a parametric study on the performance of a high aspect ratio, low speed contra-rotating fan stage. Parameters namely speed ratios of the two rotors and axial spacing between the rotors that play a significant role on the overall performance of the contra-rotating fan stage were evaluated. The rotors have a low hub-tip ratio of 0.35 and chord of 45 mm. The two rotors were designed to develop a pressure rise of 1100 Pa and 900 Pa, respectively, when operating at 2400 r/min and developing a mass flow rate of 6 kg/s. In order to evaluate the performance of the designed rotors, measurements of total pressure at the entry of rotor-1, between the rotors and the exit of rotor-2 were taken using total pressure probe rake, 4-hole probe and a Kiel probe rake. The experiments were conducted for different speed combinations of rotor-1 and rotor-2. All these speed combinations were studied separately for different axial spacing. The performance plots revealed the existence of two stall limits namely, partial stall and full stall. For lower throttle positions, rotor-2 was observed to stall. Further lowering the mass flow rate; reduces the pressure rise capacity of the stage due to stalling of rotor-1 as well as rotor-2. For the design speed operation of rotor-1 in combination with an off-design speed of rotor-2, the flow parameters change significantly. A higher rotational speed of rotor-2 generates a stronger suction effect leading to an overall improvement in the performance of the whole stage. The effect of variation in the axial spacing between the rotors was also studied. The strongest suction effect between the rotors was observed at an axial spacing of 0.9 chord.

Experimental Study of the Effect of Radially Distorted Inflow on a Contrarotating Fan Stage

“…The pressure measurement at the exit of rotor-1 allows evaluating the pressure rise across individual rotors. The presence of two possible stall regimes, partial stall and full stall, in clean flow and under circumferential inflow distortion has already been reported in Mistry and Pradeep [10]. A similar trend is observed under the hub-strong radial inflow distortion as well.…”

“…As compared to both the clean inflow and the hub-strong inflow distortion, a flatter operating range is observed. The partial stall is indicated by open circle and the full stall region is indicated towards the low mass flow rate for tip-strong radial distortion condition [10]. The stage performance characteristics are similar in trend for the various speed combinations.…”

“…Rotor-1 has 19 blades and rotor-2 has 17 blades, each with an aspect ratio of 3 and a chord of 45 mm. Details of the rotor blades and of the experimental facility are described in detail in Mistry and Pradeep [10].…”

Numerical investigation on the shock-wave and flow structures in a transonic contra-rotating axial compressor

“…[3][4][5][6] Wang et al 7 carried out an unsteady simulation on the shock-wave structure and the interaction between coupled blade rows in a contra-rotating turbine. Recently, Mistry and Pradeep 8,9 experimentally studied the effect of rotating speed, axial spacing, and so on on the performance of a low-speed contrarotating fan. A boundary layer suction flow control strategy has been experimentally studied by L Shi School of Power and Energy, Northwestern Polytechnical University, Xi'an, China et al 10 to actively improve the contra-rotating compressor.…”

The Acoustical Behavior of Contra-Rotating Fan

“…In the current investigation, both numerical and experimental studies were employed to obtain the characteristics of flow field in contra-rotating fan [3][4][5][6][7]. On axial spacing, Roy and Rao [8] tested flow behavior of contra-rotating fan.…”