M. M. Dhongadi ¹, K. V. Sreenivas Rao ², G. R. Srinivas ¹

Affiliations
1 Dayananda Sagar College of Engineering, Bangalore– 560078, Karnataka, IN
2 Siddaganga Institute of Technology, Tumkur– 572103, Karnataka, IN

Abstract

Flow at inlet of fan in an axial compressor must be one dimensional as developed flow so that angular momentum fed by the fan to incoming air is maximum. It is possible with good inlet design and optimum inlet length where we obtain stream line flow into fan with nominal boundary layer thickness. Distortion to the flow at fan inlet in an axial compressor is unavoidable problem. For example in aircraft gas turbine engine; flow at inlet of fan is distorted due to maneuvering of air craft, strong cross winds and atmospherics turbulence at inlet of compressor. Flow at inlet of fan affects boundary layer and hence the performance of compressor. Therefore, visualization of flow with boundary layers in an axial ducted fan setup is carried out for well-defined inlet conditions using pressure probes. To visualize the flow with boundary layer development at the fan inlet, static and stagnation pressure are measured throughout the inlet passage of duct using static and pitot probe and velocity is calculated across the given reference planes of duct using Bernoulli’s equation. Using these data, profile plots are drawn and mathematical models are developed and flow with boundary layer is analyzed. Under normal inlet flow condition flow in the duct inlet is axisymmetric, steady, turbulent and incompressible. Boundary layer develops consistently towards the fan inlet and it is nominal.

Keywords

Axial Compressor, Boundary Layer, Flow Visualization, Pressure Probes.

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M. M. Dhongadi ¹, K. V. Sreenivas Rao ², G. R. Srinivas ¹

Affiliations
1 Dayananda Sagar College of Engineering, Bangalore – 560078, Karnataka, IN
2 Siddaganga Institute of Technology, Tumkur – 572103, Karnataka, IN

Abstract

In axial compressor distortion at inlet leads to adverse pressure gradient at inlet of fan which leads to performance degradation and adverse effects like vibration and noise. The major distortion can lead to surge or stall in compressor. Hence, this study involves creating distortions at inlet and studying its effects on stall and performance of compressor fan. To analyze effect of distortion on compressor, an axial ducted fan is used. Study is carried out for normal flow condition, hub distortion and radial distortion conditions. Static pressure is measured in two cases. In first case, for different mass flow rate, difference in the static pressure of fan is measured, for which performance characteristic curves are plotted. In second case, normal flow inlet is distorted at operating point using above said distortion methods and difference in static pressure of fan is measured for which efficiency of fan is calculated. 60% of flow at inlet is blocked in both the cases of distortion by mechanical means using screens. Velocity across the duct at fan inlet is calculated, for which mathematical models are found. From this, average velocity from hub to tip which is necessary to find efficiency is calculated. Study shows amount of distortion not only affects stall and surge margin but also type of distortion affects surge and stall of ducted fan. Radial distortion exhibits less amount of stall margin than hub distortion for same amount of inlet flow.

Keywords

Axial Compressor, Hub Distortion, Radial Distortion, Surge and Stall.

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