A blowdown tunnel has been constructed for testing large-scale models of gas turbine blading to measure pressure distributions and losses, and for fundamental studies of boundary layers and secondary flows. It can accommodate cascades of approximately 100-mm chord, 300-mm span, and sufficient passages to achieve periodicity, or larger blades up to about 300-mm chord with fewer passages. The exit Reynolds number per metre range is 3 × 105 to 6 × 107 at unity exit Mach number, and the maximum exit Mach number is typically 1.45. These limits are well in excess of likely developments in gas turbine technology in the foreseeable future. The tunnel has a running time of 3–5 sec, which means that a small and inexpensive compressor plant is sufficient to supply the system. A pressure regulator produces a constant supply presssure regardless of line pressure fluctuations. The cascade exit pressure is controlled by tandem ejector pumps which produce sub-atmospheric conditions. The cascade Reynolds and Mach numbers may thus be independently and continuously varied.

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