The Effect of Flow Approaching Angle on the Velocity Measurement Using Bi-directional Velocity Probe

As a preliminary study for estimating the measurement uncertainty and optimal design of bi-directional velocity probe used in fire testing application, the present study has been conducted to examine the effect of Reynolds number and flow approaching angle on the measurement uncertainty of bi-directional probe. Additionally, the CFD calculation has been performed to investigate the low field near the bi-directional probe and analyze the flow c aracteristics with the flow approaching an le. The experimental result shows that the measured probe constant for high Reynolds number is slightly higher than that of McCaffrey and Heskestad while it is in good accordance with Sette's previous result. For the case of Re=3,400, the angular sensitivity between -45° and 45° well matched the previous work of McCaffrey and Heskestad and the maximum angular sensitivity reached 10% comparing to t e case of the flow approaching angle of 0°. The angular sensitivity increased with increasing Reynolds number and the maximum angular sensitivity was observed at flow approaching angle of 30°. From the CFD analysis, asymmetric wake flow was observed at the rear side of bi-directional probe at flow approaching angle of 30°, and the dynamics pressure variation inside the probe hole may affect the angular sensitivity of velocity measurement using bi-directional probe. The present study focuses on the measurement uncertainty and design optimization of bi- directional probe and can contribute to improving the reliability of fire measurement.