INVESTIGATION OF CONJUGATED HEAT TRANSFER FOR A RADIAL TURBINE WITH IMPINGEMENT COOLING

Abstract

Abstract Radial turbine is widely used in micro-turbines, turbochargers, small jet engines and expanders, and the pursue of high system efficiency has resulted in elevated turbine inlet temperatures for some of its applications, threatening its reliability. There are, however, few cooling studies on radial turbines. This paper studies the jet impingement cooling of a turbocharger radial turbine. A small amount of air (coolant), which could come from compressor discharge cooled by an intercooler, is injected through a few jet holes on the heat shield of the turbine onto the upper part of turbine backdisc, to cool the rotor blades and the backdisc. Parameters that may affect the cooling were studied by a Conjugated Heat Transfer (CHT) numerical simulation using steady flow calculations. The influences to the cooling effects by different coolant-to-turbine mass flow ratios, Coolant-to-turbine inlet temperature ratio, number of the jets etc. were analysed by a steady flow simulation. The simulation results show that, when four jet holes are placed at blade leading edge radius, using 1.0% ~ 3.0% of the main gas mass flow of coolant, the average temperature on leading edge, inducer hub and backdisc surface is reduced by 2K ~ 17K,27K ~ 65K and 51K ~ 70K respectively. Turbine efficiency is mostly reduced little over 1% point.