Experimental Investigation of the Blade Surface Pressure Distribution in an Axial Flow Fan for a Range of Flow Rates

Numerical modeling of the flow field in the vicinity of large axial flow fans finds application in various engineering investigations, whether for fan design purposes, fan induced flow fields or fan system modeling. These three-dimensional fan models generally require verification with experimental results to establish validity. For this purpose a comparison is generally made between the numerically and experimentally obtained fan performance characteristics (fan static pressure and static efficiency curves) to verify the model. Although this method provides a means to validate the numerical model on a global flow level, some uncertainty on the accuracy of this validated model on a local flow level (flow structures close to the fan blade) might still exist. In the present study an experimental technique is presented to measure blade surface static pressures that can be used to validate numerical fan models on a local flow level. These measurements are obtained for a specific fan by means of piezo-resistive pressure transducers mounted in a capsule on the fan axis and connected to pressure taps in specially manufactured fan blades. The transducers are also coupled to a telemetry system that samples the measured pressures and enables wireless communication between the fan and a laptop/PC. Blade surface pressure measurements are obtained for a series of volumetric flow rates through the fan and compared to the numerical data simulated using a RANS approach. A good comparison between the experimental and numerical blade surface static pressure data exists, with the largest discrepancies occurring near the hub as well as the leading and trailing edges of the blade. The reason for this discrepancy could be attributed, amongst others, to low y⁺ values (y⁺ < 30) on the blade surface in these regions, leading to errors in the calculation of the wall condition by the wall function. The experimental technique therefore provides CFD engineers with an additional tool for numerical fan model validation on a local flow level.