Investigation of backface cavity sealing flow in deeply scalloped radial turbines

Abstract

The backface cavity sealing flow in deeply scalloped radial turbines is numerically investigated in this article. Both the time-averaged and unsteady results are shown, and three cavity sealing geometry models are analyzed. It is found that the the sealing flow strengthens the backface casing scraping flow in the lower radial region of backface clearance, cools the root of the blade backface and prevents hot gas ingestion. With the same disk radius ratio, the model with a radial clearance shows a better performance on cooling and sealing effectiveness than that with an axial clearance. The model with a radial clearance and a larger disk radius ratio has a higher isentropic efficiency. However, the axial thrust increases drastically and the cooling effectiveness is very low. Furthermore, the sealing effectiveness for the model decreases sharply because of the larger circumferential pressure difference near the disk rim and the higher rotational Reynolds number. In transient state, the amplitude of pressure and temperature increases significantly near the disk rim. And an unsteady flow pattern with high pressure and ingestion zones rotating at twice the rotational speed in the counter rotating direction, is found on the disk backface surface.