The Transient Heat Transfer Facility (THTF) was developed
at the University of Oxford to test full-scale high pressure compressor
and turbine casing air systems using gas turbine engine
representative secondary air system mass flow rates, total
temperatures and total pressures. Transient casing response
together with blade and disc responses governs achievable tip
clearances in both compressors and turbines. In this paper
we investigate the use of air impingement as a means to speed
up the casing response. Two different
impingement configurations were selected from a total of
eight designs based on steady RANS predictions of maximum HTC.
The 3D thermal growth of the casing was characterised by the
surface temperature rise over a given period of time to assess
achievable dynamic response.
The experimental set-up resembles a typical aircraft engine
and therefore includes measurement uncertainties arising from features such as fixtures, seals, geometries and large surface
areas that are then subjected to varying thermal inertias.
These can lead to circumferential temperature non-uniformities,
as evident from the experimental results. The experimental data was then compared
against numerical predictions from an axisymmetric, 90° sector,
conjugate heat transfer model of the facility using the two impingement
plate designs. The combined experimental and numerical study
shows the significance of analysing the full annulus, at engine
representative conditions and the benefit of an impingement array
to potentially speed up casing response for future engines.