Jet impingement heat transfer in rotating coolant passages

Abstract

In gas turbine engines, increasing turbine inlet temperature increases engine thermal efficiency but also increases the amount of heat transferred to the turbine blades. To achieve reasonable turbine blade durability goals, the blades are cooled with air extracted from the compressor but at a penalty to the efficiency. Advanced turbine blade design employs jet impingement cooling for internal blade surfaces. Using stationary models, many tests have optimized impingement designs for turbine operating conditions. However, rotation of turbine blades introduces centrifugal and Coriolis forces on the coolant inside the blades. These forces alter coolant motion and thus heat transfer for internal blade surfaces. Therefore, tests have been conducted to obtain local heat transfer coefficients and the coolant flow distribution for rotating channels with impingement cooling by arrays of circular jets. Additional stationary tests serve for a baseline and for comparison with other investigations. Results of this study are important to turbine rotor blade coolant passage design. Jet flow direction was in the direction of rotation in one channel and opposite to the rotation direction in the other channel. The air jets impinged normally on smooth target walls. Heat transfer and flow distribution results are presented for these two target walls. Two flow exit configurations were studied: flow exited both channels in a single direction, radially outward, creating cross flow on jets at larger radii, and flow exited through extraction orifices in each target wall creating little cross flow on other jets. Jet rotation number, EIDN,, was varied from 0.0 to 0.0055 and the isolated effects of jet Reynolds number (2500 to 10,000), rotation speed (0, 400 and 800 rpm) and heated wall-to- coolant temperature difference (AT = 11, 28 and 45K) were measured. Also the number of extraction orifices was reduced by 50%.