A new method based on laser light scattering was developed to detect a radial inflow of gas inside a rotating-disk system. Ambient air was seeded with small particles that followed the flow. Once entering the wheel space between rotor and stator, these particles crossed a laserbeam emitted by an At+-Laser. The scattered light was detected by a photomultiplier whose electrical output signal was finally processed in a data acquisition system. The signal intensity thereby indicated the strength of ingress.

The measuring technique was adapted to a shrouded rotor-stator system in a quiescent environment and an experimental investigation was conducted to determine the minimum cooling flow rate necessary to just prevent ingress (Cw,min) for several seal clearance ratios and two different rotor disk geometries. The results were correlated to the disk rotational Reynolds number and compared with data yielded by applying a pressure criterion. With the rotating disk being 0.5m in diameter and spinning at max. 10000rpm, rotational Reynolds numbers up to 3.8×106 were achieved. The results show an expected behaviour for the seal clearance variation and an unexpected behaviour for the two disk geometries. Compared to the new technique, the pressure criterion underestimates the minimum purge flow. Additional experiments were conducted for a single seal configuration to demonstrate the new method’s capability to acquire the sealing effectiveness. The results are intriguing but also show that further investigations must be conducted to establish this new technique.

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