Multi-hole probes

1. Multi-holeprobes • simple and robust probe for the measurement of flow velocity and direction ( V : velocity magnitude, aT : pitch angle, bT: yaw angle) • Incident angle up to +/- 60 deg (5-hole probe) +/- 70 deg (7-hole probe) • Measurement of hole pressures → calculation of pressure coefficients → calculation of V, aT, bT using calibartion constants. • Calibration in wind tunnel needed to determine calibration constants.

2. Multi-holeprobesto be used • A 5-hole probe of own design • 4 mm diameter, 45°cone angle, soldered of copper • Short flexible tubing connecting the probe to the sensor circuit board The pressure sensor used • Sensortechnics HCLA pressure sensors: • will be located on a circuit board not far from the probe • 12 bit A/D resolution, 0.25% uncertainty • Response time 0.5 ms → temporal resolution well above 100 Hz • readout digitally through I2C bus

3. Calibrationrig • A small wind tunnel used to set the reference wind speed • 0-24 m/s • 0.35 x 0.35 m free jet test section • turbulence intensity < 0.8% • Calibration rig to mount the probe and to set up pitch and yaw angle • Controlled by 2 stepper motors • Fully automatic calibration possible. The wind tunnel to be used for calibration • Current project status: • probes already manufactured, • calibration rig is almost ready • test progrem in LabVIEW is under development • calibration expected in the following month. Components of the 2D calibration rig