The contemporary design philosophy behind novel aircraft concepts is inclined towards tighter integration of airframe and propulsors. Although embedded engines show potential fuel benefit, on a component level, the fan performance is adversely affected due to the non-uniformity of the ingested boundary layer. The distorted flow undergoes three-dimensional redistribution around the spinner as it approaches the fan. The redistribution results in non-axisymmetric off-design conditions at Aerodynamic Interface Plane of a fan. Therefore, the redistribution leads to the losses. Although many past studies have addressed this problem, a parametric study on distortion index and experimental velocity measurements in redistribution region are missing.    
   The present study shows the effect of varying the distortion index on three aspects of fan operation: performance curve, near stall points, and the upstream flow topology. A low-speed axial fan is tested under the circumferential total pressure distortion. The distorted sector spans over sixty degrees. The distortion index is varied parametrically.  Planar and stereo Particle Image Velocimetry (PIV) are applied to measure the flow redistribution upstream of the fan. Note that this is one of the first studies where PIV is applied to study the redistribution of the distorted flow. Total pressure downstream of the fan is measured with a pressure rake. Noise measurements are carried out using a microphone. Stall points on the performance curves are identified by analysing the noise spectrum. It is observed that with increasing distortion index, overall performance curves shift to lower loading coefficients and the near stall points occur at higher flow coefficients (earlier). Therefore, the stall margin is reduced. This trend is in agreement with the literature.  
   It is found that for a constant wall thickness of the distortion screen, the distortion index varies linearly with the grid porosity. However, the topology of the generated distortion is different at low grid porosity, where a counter-rotating stream-wise vortex pair is observed. However, no evidence of this vortex pair is observed downstream of the fan.   
  The present study overcomes the limitation of the previous experimental study. In past studies, the upstream pressure measurements did not cover the region below the hub radius. In the present study, PIV overcomes this limitation and provides velocity field in the whole range of radius, including at the spinner tip. This provides further insights into the flow redistribution around the spinner. The velocity field is also measured without the distortion. Subtracting the clean velocity field from the distorted flow clearly shows how upstream flow is modified under distortion. This allows us to quantify the redistribution of momentum from clean flow to the distorted flow.   
   It is clear from the velocity field that the presence of spinner plays an important role in flow redistribution. Therefore, it also identifies the potential of modifying spinner geometry to increase the redistribution and reduce the adverse effect of distortion. This will be a part of future studies.  
   

 


Performance of a Low Speed Axial Fan Under Distortion: An Experimental Investigation

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

Turbo Expo - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.