Nonsteady Flow in a Turbocharger Nozzleless Radial Gas Turbine

Results of an extensive test program investigating the nonsteady flow performance of a nozzleless radial gas turbine in a special rig show that the measured mass flow rate and power are different from predicted values using turbine steady flow test data. Furthermore, when the results are correlated against the form factor and pulse frequency, the overall mass flow predictions are substantially independent of these two parameters but the power predictions are strongly influenced by them. Measured power to the predicted power based on steady flow data decreases as the pulse shape approaches sinusoidal form, thus indicating that the internal losses in the turbine are related to the nonsteady flow conditions within it. The tests showed that the form factor was dependent on pipe length, pulse frequency, mean pressure in the pipe, and turbine casing size. For the rig there was an optimum form factor for each combination of pipe, turbine casing, and mean pressure ratio across the turbine. It is deduced that the pulse shape is not only dependent on the normal factors, such as pipe diameter and length, and turbine cross-sectional area, but also on scroll length, and that this, in turn, influences the nonsteady flow within the turbine.