Deduction of temperature fluctuations in transient compression wind tunnels using incompressible turbulent flow data

Wind tunnels and other aero-thermal experimental facilities are likely to make a contribution to the optimisation of energy and propulsion systems for the foreseeable future. Short duration wind tunnels such as shock tunnels and gun tunnels rely on a transient compression process and are likely to generate significant turbulent fluctuations in the nozzle reservoir region. In the present study, the magnitude of likely stagnation temperature fluctuations in two such facilities is inferred from incompressible temperature fluctuations data obtained by other workers. The friction velocity Reynolds numbers for the gun tunnel and shock tunnel cases considered presently were Reτ =31,579 and 24,975 respectively. The RMS stagnation temperature fluctuations, when averaged over the pipe flow diameter, are estimated to be 14.6 and 278 K for the gun tunnel and shock tunnel cases respectively. The estimated RMS value in the case of the gun tunnel is significantly larger than the experimental value previously measured on the centre line of the gun tunnel nozzle of 2.3 K. The difference observed between the inferred and measured temperature fluctuations in the gun tunnel case may be related to spatial variations in the temperature fluctuations. In the case of the shock tunnel, the magnitude of the fluctuations is demonstrated to be significant for supersonic combustion experiments. The present approach for estimating the magnitude temperature fluctuations should be refined, but more detailed measurements of temperature fluctuations in such facilities are also required.