Browsing by Author "Von Backstrom, T. W."

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    Performance of rotor-only axial fans designed for minimum exit kinetic energy
    (South African Institution of Mechanical Engineers, 2002) Van der Spuy, S. J.; Von Backstrom, T. W.
    The major loss source in rotor-only axial fans is the kinetic energy associated with the axial and circumferential components of the exit flow. This paper investigated the aerodynamic and acoustic performance of two fans designed to produce minimum exit kinetic energy. The first was a general application fan and the second a low-noise fan with large-chord forward-swept blades. The fans were tested for fan noise and performance in accordance with BS 848. The low-noise fan was the quieter and more efficient of the two fans, whilst both fans were quieter and more efficient than an existing typical general application fan, of unknown design. The results underlined the importance of following a well-defined design methodology when designing rotor-only axial flow fans.
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    Slip factor prediction for impellers with straight, back-swept blades
    (SAIMechE, 2019) Von Backstrom, T. W.
    ENGLISH ABSTRACT: Slip factor accounts for the deviation of the flow angle from the trailing edge blade angle at the exit of radial impellers. Accurate values are required to predict impeller torque and energy input. The slip factor prediction method for back-swept radial bladed impellers is based on the so-called single relative eddy (SRE) method, which is an approximation of the classical, two-dimensional analytical solution to the inviscid flow problem. The relatively accurate prediction of the slip factors of 19 impellers found in four data sets published since its formulation, shows the reliability of the SRE method. The characteristics of straight-bladed impeller layouts are explored and incorporated into the SRE method. It turns out that the SRE method as developed for logarithmic spiral blades predicts the inviscid flow slip factor of 42 different straight bladed impeller geometries accurately, when a correction for the critical radius ratio at low blade numbers is introduced. Predicted slip factor values are also compared to new experimental data for five different impellers with straight, back-swept blades, over a range of three blade angles and three blade numbers. Agreement is excellent near the flow coefficient corresponding to the volute design angle.
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    Unsteady analysis of a generic non-axisymmetric hub endwall contour as applied to a rotating turbine at on and off- design conditions
    (SAIMechE, 2018) Dunn, D. I.; Von Backstrom, T. W.; Sneddenc, G. C.
    Numerous researchers have investigated various techniques to reduce loss in gas turbine engines. One such technique that has shown promise is endwall secondary flow control using non-axisymmetric endwall contouring. Previous steady state investigations have shown that the generic endwall contour designed for a cascade reduced the loss in a rotating turbine test rig. The current investigation was to determine if there were unsteady effects introduced by the contour at design and off design conditions. An experimental and numerical study was performed to investigate the rotor flow field for any unsteady changes to the rotor exit flow field. The investigation was performed at an increased loading condition, design and a decreased loading condition to determine how changes in operating condition altered the flow field. The experimental results showed that the velocity magnitude of the hub endwall secondary flow vortex system for the contoured rotor was reduced. The peak difference in oscillation of the flow was also reduced. The effect of the endwall contour reduced the over and under turning of the endwall secondary flow vortex system as well. The magnitude of the FFT at the blade passing frequency was reduced below midspan.