Design and Development of a Fast Response Torque Meter for Unsteady Flows in Turbocharger Applications

A high-speed torque meter has been designed and tested for turbocharger applications in order to assess the effect of unsteady boundary conditions. The torque meter is designed using the shaft-twist method by measuring the change in relative angle between the two ends of the drive shaft. Two encoder wheels are mounted on either end of the shaft and a high-speed FPGA measures the variation of time between edges from optical switches. The angular twist in the shaft is calibrated against a reference torque transducer over a range of torque values. The torque meter is installed on an existing compressor rig testing facility at Imperial College London equipped with a pulse generator capable of producing different pulse frequencies and amplitudes. To test the response to unsteady conditions, a centrifugal compressor is driven under a pulsating backpressure while torque is measured at the drive shaft. The torque measurement is compared against static pressure measurements corresponding to the pulsating conditions. Twelve combinations of frequency and pulse amplitudes have been tested. Due to its simple construction and development, the authors believe that where high-speed measurement equipment is already in place, effective torque measurements of this kind can be added with a low cost to help explore unsteady performance in turbomachinery.