Velocity measurements using the photon correlation technique in a separated boundary layer

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Abstract
A photon correlation system employing a Bragg cell to frequency shift the incident laser light has been used to measure mean velocities and turbulence intensities in the separated flow behind a backward facing step. Theoretical relationships are derived relating the probability density of flow velocity to the count correlation, these results being applicable to the case of unseeded air flow. The method can be used for measuring in flow regions where there are very high local turbulence levels, outside the range of more conventional techniques. Good agreement was found with previous measurements recorded using hot‐wire anemometry.