Influence of Circumferential Inflow Distortion on the Performance of a Low Speed, High Aspect Ratio Contra Rotating Axial Fan

Abstract

The influence of circumferential inflow distorted on the performance and flow behavior of a high aspect ratio, low speed contra rotating fan is reported in this paper. The total pressure at the inlet is artificially distorted by means of 90 deg mesh sector with a porosity of 0.70. The performance of the contra rotating fan was studied under different speed combinations of the two rotors under clean and distorted inflow conditions. Detailed flow analyses were conducted under design and off-design conditions. In order to understand the effect of distortion and its extent, the distortion sector was rotated circumferentially at intervals of 15 deg to cover the entire annulus. Detailed measurements of the total pressure, velocity components, and flow angles were carried out at the inlet of the first rotor, between the two rotors, and at the exit of the second rotor. The study reveals a few interesting aspects on the effect of inflow distortion on the performance of a contra-rotating stage. For the design speed combination and lower rotational speed of rotor-2, a reduction in the overall operating range with a shift of the peak pressure point towards higher mass flow rate, was observed. It is observed that the effect of inflow distortion at the inlet of rotor-1 gets transferred in the direction of rotor-1 rotation and spreads across the entire annulus. The opposite sense of rotation of rotor-2 causes the distortion effect to get transferred in the direction of rotation of rotor-2 with an associated reduction in the total pressure near the hub. It is observed that a higher rotational speed of the second rotor has a beneficial effect on the overall performance due to the strong suction by generated higher rotational speed of rotor-2.

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

“…Higher aerodynamic loading can be observed nearly about 60% span to 90% span. This is in line with the design of the rotors with higher loading near the tip region [11]. The magnitude of the pressure coefficient near the tip region decreases.…”

“…The performance of the stage is found to be improved with the increase of the rotational speed of rotor-2, which is similar to what is observed for the clean inflow condition [11]. For the distorted inflow condition, up to 45% span is found to be significantly affected showing a reduction of the pressure coefficient in that region for all the speed combinations.…”

“…The study focuses on the effect of different speed combinations of the rotors on the performance of the contrarotating stage. This particular axial spacing was chosen based on the observations reported in Mistry and Pradeep [11]. The speed of rotor-1 was maintained constant at a design speed of 2400 rpm (referred to as ) and the speed of rotor-2 was varied as 2200 rpm, 2400 rpm, and 2600 rpm, respectively, denoted as 0.91 , , and 1.08 .…”

Propagation of Different Types of Inflow Distortions through a Contra Rotating Fan Stage

“…Under circumferential inflow distortion the performance of rotor-1 is lower than [27]. For hubstrong complex inflow distortion, the performance (in terms of pressure rise) reduces by about 3% and so does the overall operating range.…”

Numerical Investigation for the Impact of Single Groove on the Stall Margin Improvement and the Unsteadiness of Tip Leakage Flow in a Counter-Rotating Axial Flow Compressor

“…Endeavors to gain further insights into the flow physics in CRAC have been conducted on the important factors, including axial spacing between two rotors, unsteady effects, inlet distortion, etc. [30][31][32][33][34][35][36][37][38]. Compared with a conventional compressor stage, it was found that there are many new characteristics and unique flow phenomena in CRAC.…”