Scaling overall metal effectiveness from ECAT rig to engine conditions

This project falls within the EPSRC Engineering research area.

This project is sponsored by Rolls Royce.

Jet engines operate at temperatures above the melting point of the metal vanes and large temperature gradients cause large thermal stresses that can severely limit the lifetime of engine components. Cooling systems have been developed and applied to components within a gas turbine engine. The high-pressure nozzle guide vane (HP NGV) is the row of stators at the first stage of the turbine, immediately downstream of the combustor. It is subject to a non-uniform inlet total temperature profile and high temperatures.

Existing research has focused on optimizing efficiency of NGV cooling systems. Few experiments have been performed at engine conditions with real engine parts as it is very expensive to supply the required high temperatures and pressures. Thus, most experiments are carried out in low-temperature, low-pressure cascade facilities with high levels of non-dimensional similarity between engine and rig conditions. Despite the high level of similarity, some scaling parameters are commonly unmatched, including the coolant-to-mainstream temperature ratio.

The Engine component aerothermal facility (ECAT) is a highly matched rig for testing NGV cascades. The high-level objective of this project is to determine a robust procedure for scaling metal temperature data from ECAT in order to accurately predict in-service HP NGV metal temperatures. To our knowledge, no such scaling procedure has been presented in available literature. This scaling procedure would benefit both Rolls Royce and the wider aerospace industry as the only present method for experimentally predicting in-service metal temperatures is the thermal paint test. This can only be carried out late in the development process and the boundary conditions of such a test are typically very difficult to determine, so it is challenging to obtain meaningful results from paint tests. The scaling procedure developed in this project will allow for accurate prediction of in-service metal temperatures from testing done in large-scale rigs (such as ECAT) earlier in the development process in an environment with known boundary conditions.

This project involves three scaling processes to facilitate understanding of the required scaling procedure and satisfy the high-level objective. The first process is a low order virtual experiment, that will be carried out in MATLAB and with Rolls Royce tools. The outcome of this will be the assessment of differences between engine and ECAT rig conditions, and to determine simple approximate scaling rules. To our knowledge, no study in the available literature has proposed scaling rules for metal temperature as a function of other non-dimensional parameters.

The second process is a high order virtual experiment, in the form of a fully conjugate computational fluid dynamics large eddy simulation (LES). The outcome of this will be the assessment of differences between the two cases and verification of the simple scaling rules obtained from the low order virtual experiment. To our knowledge, no study in the available literature has performed a fully conjugate LES simulation of a flat plate so this is intended to provide novel understanding of the various physical mechanisms that affect the scaling procedure from rig to engine conditions and an insight into the relative importance of various scaling parameters when it comes to considering the degree of matching required in experimental rigs.

The third process is scaling metal effectiveness results from ECAT to engine conditions and comparing to Rolls Royce thermal paint test results.