Effect of Speed Ratio and Axial Spacing Variations on the Performance of a High Aspect Ratio, Low Speed Contra-Rotating Fan

Abstract

This paper explores the effect of speed ratio and axial spacing between high aspect ratio, low speed contra-rotating pair rotors on their aerodynamic performance. The blades were designed with a low hub-tip ratio of 0.35 and an aspect ratio of 3.0. Numerical and experimental studies are carried out on these contra-rotating rotors operating at a Reynolds number of 1.258 × 105 (based on blade chord). The first and second rotors were designed to develop a pressure rise of 1100 Pa and 900 Pa, respectively, for total mass flow rate of 6 kg/s when both operating at a design speed of 2400 rpm. The performance of the fan was evaluated based on variations of total pressure and flow angles at off-design operating conditions. The measurementsof total pressure rise, flow angles etc. are taken upstream of the first rotor and in between the two rotors and downstream of the second rotor. The performance of the contra rotating stage is mainly influenced by the axial spacing between the rotors and speed ratio of both the rotors. The study reveals that the aerodynamics of the contra-rotating stage and stall margin is significantly affected by both the speed ratio as well as the axial spacing between the rotors. It was found that with increasing the speed ratio, the strong suction generated by the second rotor, improves the stage pressure rise and stall margin. Lower axial spacing changes the flow incidence to the second rotor and thereby improves the overall performance of the stage. This however, is accompanied by an increased noise level. The performance is investigated at different speed ratios of the rotors at varying axial spacing. Detailed numerical simulations have been conducted using ANSYS CFX13© using mixing plane approach between rotors. Numerical simulations are compared with experimental results at off-design conditions. These results are validated using the experimental data. Numerical simulations are expected to provide deeper insight into the flow physics of contra-rotating rotors which may be difficult to capture experimentally.

Numerical investigation of the unsteady flow behaviors in a counter-rotating axial compressor

“…10,11 To obtain a deeper insight into the flow physics in CRAC, a large amount of work has been carried out on the effects of some major factors such as rotor stagger angle, pitch-chord ratio, inlet distortion, casing treatment, speed ratio of the two rotors, axial spacing between two rotors, etc. [12][13][14][15][16][17][18][19] Results showed that those factors have significant impacts on the performance of CRAC. So as to understand the tip clearance size effect on the overall performance and TLF, Gao et al 20 and Wang et al 21 have conducted steady numerical simulations on several tip clearance sizes for both rotors.…”

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

“…This may be due to the inverse design concept with stacking of the front rotor along trailing edge and along leading edge for the rear rotor. Mistry and Pradeep 14,15 have recently reported design and preliminary performance analysis of a high aspect ratio contra-rotating axial flow fan stage.…”

Investigation of Speed Matching Affecting Contrarotating Fan’s Performance Using Wireless Sensor Network including Big Data and Numerical Simulation

“…Experimental studies showed that variable speed matching can improve the work stability [16]. Mistry and Pradeep [17,18], through experiments and numerical simulations, reported a study of speed ratio on the performance of a contrarotating fan stage. Results showed that with increasing the speed ratio, the strong suction generated by the second rotor improves the stage pressure rise.…”