Numerical analysis and preliminary experimental heat transfer measurements on a novel rotating leading edge model

This paper reports the preliminary findings of an investigation, conducted at the University of Florence within a national research project, devoted to the analysis of the flow field and heat transfer in a high pressure turbine blade leading edge (LE) cooling system under rotating conditions. A rotating test rig was designed in order to investigate a scaled up model of a simplified LE cooling system. The investigated test article is composed by a trapezoidal duct which feeds the LE cavity through three large racetrack holes generating coolant impingement on the internal LE surface. Air is then extracted by means of 4 rows of 6 holes, 2 for shower-head and 2 for filmcooling. The effect of the pressure drop between pressure and suction side is reproduced by three plenum that allow variable coolant mass flow rate extraction from each cooling row, providing realistic flow conditions inside the leading edge cavity. Heat transfer coefficient distribution on the internal leading edge surface was evaluated through a steady state measurement technique. A constant voltage drop was applied on a Inconel sheet providing a constant heat flux on the test section; the wall temperature was measured exploiting wide band thermochromic liquid crystals. The test rig was designed to reach typical actual engine ranges of jet Reynolds number (from 10000 to 40000) and Rotation number (from 0 to 0.05) for three crossflow cases representative of tip, mid and hub of the blade respectively. The aim of current contribution is to present the results obtained in a preliminary experimental and numerical campaign performed under stationary conditions. Both the jet Reynolds number and the cross-flow condition effects on the heat transfer distribution were investigated from the steady state measurements. Experimental results were also used to support the validation of a reliable CFD model to permit an in-depth analysis of the investigated test cases. It is particularly interesting, for example, to assess the flow-field development into the leading edge cavity, in order to evaluate how it affects the heat transfer LE distribution. A RANS steady state approach was used to perform the numerical analysis, which was carried out using the commercial CFD code ANSYS CFX® v15 exploiting the k-ω SST turbulence model. A comparison between obtained numerical and experimental HTC distributions on the leading edge surface is presented in this paper, showing a fairly good agreement.