DESIGN ASPECTS FOR LARGE DIAMETER, LOW SPEED AXIAL FLOW FAN FOR WIND TUNNEL APPLICATION

A large diameter, low speed axial flow fan has been designed to drive the Centre for Railway Research (CRR) wind tunnel at HT Kharagpur. Total pressure rise of 1400 Pa is required from the fan at the design mass flow rate of 420 kg/s. The outer diameter of the fan is 4 m with 0.6 hub to tip ratio. The present paper discusses the design methodology and computational analysis of wind tunnel fan. The design methodology includes a preliminary mean line analysis using the fundamental governing equations and CFX inbuilt design module. Subsequently, detailed computational analysis of the rotors was carried out using ANSYS CFX (R). Based on the results obtained from the CFX analysis, the mean line analysis was modified to achieve the desired performance of the rotor. Parametric study was undertaken with different blade number combination, axial spacing, blade chord length, location of maximum thickness, leading edge profile, etc. The selection of number of blades for rotor and stator is an important aspect for such fan design in terms of cost, utility installation and noise. For low background noise in wind tunnel higher number of blades with suitable combination was selected for the fan ensuring the tone noise (produced by interaction of rotor and stator) is generated at attenuable frequencies. The blade angles, chord lengths, blade camber were optimized for good aerodynamic performance in terms of blade loading, wake thickness, hub-tip pressure profile, overall efficiency and pressure rise. It is strongly believed that discussed design aspects in terms of selection of various geometrical parameters for wind tunnel fan will give useful guidelines for future design of a low speed, large diameter fan of such capacity.