LDV measurements in a Navy CPS fan

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Date
1991-09-05
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Virginia Tech
Abstract

New ventilation fans for Navy ships need to filter chemical agents from the supply air. This requires much greater pressure ratios than in earlier fans. This research was conducted to understand the performance of these new fans. LDV measurements of axial and tangential velocities were made in a Navy fan from upstream stations, throughout the blade row, and downstream into the stator. Data were collected two ways: (1) averaged over the entire rotor cycle and (2) averaged at each rotation angle.

Upstream bimodal probability densities of the axial velocity component were found in the cycle-averaged data. Bimodal distributions indicate instabilities in the stagnation or separation lines or vortex shedding. The phase-averaged data show there to be a dependency of velocity on rotor positions.

Downstream profiles mapped the large separation region downstream of the rotor. The downstream region shows recirculating flow and reattachment as the flow moves into the stator section.

Phase-averaged profiles in the stator inlet plane show the periodic rotor wake as it enters the stator. The resulting flow angle does not match the stator angle. In the blade row, the phase-averaged velocity profiles show negative tangential velocities near the leading edge and separation occurring near midchord. The region influenced by the separation extends across most of the blade passage as the fluid approaches the exit plane of the rotor. The separation in the blade row contributes to the poor performance of the fan and low pressure recovery.

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