Effect of Solidities and Nozzle Flow Angles on a Partially Admitted Small Axial-Type Turbine

Abstract

The performance characteristics of a partially admitted small axial-type turbine are experimentally studied with changing design parameters, such as the exit flow angles at the nozzle and solidities at the rotor. The tested turbine consists of a single stage and its mean radius is 35 mm. This small turbine could be applied to an air tool driver, which usually uses a vane-type rotor. If an axial-type turbine rotor is applied to the driver instead of a vane-type rotor, it could operate without friction and abrasion because the turbine rotor does not make contact with its casing. In order to maintain these merits in the turbine without reducing power and with a limited mass flow rate, the performance tests are conducted at partial admission. When an axial-type turbine is operated at partial admission, the design parameters are changed from the suggested design parameters obtained from the full admission because the flow loss mechanisms are different. In this experiment, three different solidities and four different nozzle flow angles are applied to find the optimal design parameters. To compare the turbine performance, the net specific output powers are evaluated. The test results show that the impulse force is a more important factor than other design parameters for partially admitted small turbines to obtain high output power. For a 3.4% partial admission rate, the best performance is obtained when the rotor solidity is at 2.18, which is increased by 74% compared with the typically recommended optimum solidity at full admission.