Experimental Investigation of the High Turbulence Wake, for Measurement of Drag Force

Momentum difference method can be used for measuring drag force. In this method, using velocity and turbulence intensity distributions at the model downstream, drag coefficient is determined. If the turbulenceintensity downstream of the model is high, turbulence will not be uniform (homogenous) and measurements by one-dimensional hot-wire probe will be associated with error. In this experimental investigation, turbulence intensity downstream of a rod has been studied and the minimum distance at which the flow turbulence can be considered with acceptable uniformity(homogeneity), has been determined. Turbulence intensity at the rod downstream, decreases with increase in X/D ratio, so that the maximum turbulence intensity at a distance of 25 times the downstream diameter reduces to %10 and error in measurement of drag coefficient at this distance is about 8%. at the distance of 35 times the downstream diameter, the maximum turbulence intensity reduces to about %7 and the measurement error is about %5. In this study, a hot wire anemometer has been used to investigate velocity distribution and air flow turbulence intensity at the rod downstream at Reynolds numbers of 1570 to 10470.