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Abstract. Heat flux gauges at a flat plate are designed suited to measure the heat transfer in transition boundary layers. The measuring technique employed (cold thin films) is convenient for transient experimental facilities (such as a Ludwieg tube). The development of a well defined and optimized sensor design is discussed.

The influence of free stream turbulence intensity on boundary layer transition was studied for a weakly compressible flow along a flat plate. The test facility consisted of a Ludwieg tube in which values of Mach number, Reynolds number and free stream turbulence could be varied over the following ranges: 0.09 < M < 0.6, 5.105 < Reu/m < 1.107, 1.2% < Tu < 9%. In this paper the turbulence intensity was varied up to 4.0 %. Unsteady heat flux to the flat plate was measured using cold thin film gauges. From these measurements, the intermittency was computed using an integral technique. For turbulence intensities of 1.2 %, the intermittency distribution is somewhat below the Narasimha and Johnson model, whereas a good agreement is obtained for a free stream turbulence intensity of 4.0 %. The calculated dimensionless spot production rates is proved to agree very well with existing data sets from other experiments. For a Mach number equal to 0.36 the production rates seems a bit higher when compared to the incompressible data. However, the differences are small.

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