Session: 13-02 Heat Transfer Testing & Instrumentation

Submission Number: 178411

High-Accuracy Transient Thermal Measurement Technique By Ramp Heating in Tip Cooling of a Transonic Turbine Blade 

Heat transfer experimental accuracy is crucial for thermal design and durability of turbine blades, but transient thermal measurement, as a popular tool to test external heat transfer design under transonic conditions, suffers from high uncertainty that is typically above 10%. One error source is associated with the prevalent use of step heating in mainstream, leading to an abrupt climb in wall temperature that is difficult to be sampled accurately by regular sensors. To mitigate this error, ramp heating method is applied to transient thermal measurement of film cooling in transonic turbines, for the first time in open literature. In this paper, heat transfer experiments were conducted for film cooling on a flat tip of transonic turbine blade, using infrared thermography with both step and ramp heating methods. Experimental data demonstrate that ramp heating method significantly enhances the robustness of linear regression, i.e. desensitizing tip Nusselt number results to the selection of the onset of data reduction period, thus reduces regression uncertainty by 57%, and run-to-run error by 31%, compared to step heating method. To accommodate ramp heating in mainstream, a new data reduction theory and procedure is developed, namely “iterated linear regression technique”, which iterates adiabatic effectiveness to search for the optimum regression performance. This is necessary because adopting ramp heating method directly in conventional transient thermal measurement technique produces inconsistent results of Nusselt number with respect to step heating method. The newly-proposed technique eliminates this inconsistency by making more reasonable assumptions to deal with the time-variation of mainstream-to-coolant temperature ratio during ramp heating, and is recommended for high-accuracy transient thermal measurement of film cooling in transonic flows. 

Presenting Author: Jiabo Cui Shanghai Jiao Tong University

Presenting Author Biography: Mr. Jiabo Cui is a PhD student in Shanghai Jiao Tong University. His research interest is gas turbine heat transfer and film cooling, with a focuse on high-speed flows.

Authors:

Haiteng Ma Shanghai Jiao Tong University
Jiabo Cui Shanghai Jiao Tong University