Design and testing of a highly loaded mixed flow turbine
A method of designing a new generation of highly loaded mixed flow turbines for turbocharger application is described. A review of the published work concerning radial turbines and closely related to mixed flow turbines is presented. A 1-D design method was developed. It is used to define the over all turbine dimensions and to analyse its performance at the off design conditions. The method is applicable to both radial and mixed flow turbines. A series of designs had been produced and then analysed by the off design performance prediction method. The effects of several geometrical parameters on the performance of the designs were investigated. This had led to the selection of an optimum rotor design for further analysis. An analytical method based on the Bezier polynomials is used to define the three dimensional blade geometry . The rotor geometry is optimised by means of a quasi three-dimensional method for the flow analysis. The effect on the flow inside the rotor of three factors influencing the blade geo metry has been investigated. These consist of the rotor blade angle variation along the leading edge, the rotor length and the blade curvature. Two mixed flow turbine prototype s have been manufactured and experimentally tested. These differ mainly in the rotor inlet, which is a constant blade angle in one case, and a notionally constant incide nce ang le at design conditions in the other case. The former turbine showed significantly higher efficiencies across the operating range, and possible reasons for this are discussed. The experimental analysis concerns the measurement of the turbine overall performance, the pressure distribution along the rotor shroud and the flow field downstream of the rotor exit.