Doctoral Degrees (Mechanical and Mechatronic Engineering)

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Browsing Doctoral Degrees (Mechanical and Mechatronic Engineering) by Subject "Aerodynamics -- Research"

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    A numerical procedure for predicting the effects of distorted inflow conditions on the performance of axial flow fans
    (Stellenbosch : University of Stellenbosch, 1991-03) Thiart, G. D.; Von Backstrom, T. W.; University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering
    ENGLISH ABSTRACT: A numerical procedure for predicting the effect of inlet flow distortions on the performance of axial flow fans is proposed. The study is aimed specifically at fans of low solidity and low hub-to-tip ratios, which have attained some importance with the advent of large directly air-cooled power stations in certain arid regions of the world. The numerical model is an extension to cylindrical polar coordinates of the SIMPLEN algorithm that has been developed by the author previously. The algorithm is implemented in a computer code, FLOVAX, which solves the incompressible Navier-Stokes equations, augmented by the k-Ɛ model of turbulence, on a computational domain that is aligned with the cylindrical polar coordinate system. Several relatively simple flow problems are solved to verify the code: laminar stagnation flow, laminar flow near a rotating disk, turbulent flow near a propeller, turbulent flow through an abrupt axisymmetric expansion, and turbulent swirling flow in an annulus. Good agreement is obtained between the numerical solutions and the corresponding analytical, empirical or published experimental and numerical results. Some experimental results are also presented: measurements of shaft power, volume flow rate and static pressure rise were taken in a setup comprising an axial flow fan mounted in the wall of a wind tunnel. The wind tunnel was used to provide flow across the fan intake, thus establishing distorted inflow conditions. Detailed measurements of the velocity and static pressure distributions in the duct downstream of the fan rotor were also performed. It is clear from the results that flow across the intake of the test fan has a detrimental effect on its performance in that an increased amount of power is necessary to deliver the same flow rate as with no crossflow. In the numerical predictions, blade element theory is used to model the thrust and torque exerted by the fan blades on the air. The numerical results generally confirm the results of the experiment, although the increase in power is underestimated: an increase of only approximately half of the measured increase is predicted. Several recommendations for improvement of the numerical procedure are made.