Flow Characterization of an Experimental Rotor Rig using a Hot Film Probe

Abstract

A horizontal axis helicopter rotor rig was developed in this study and early model testing was completed using a 2D cross wire hot film probe. The motivation of study was to identify the flow characteristics that could be determined using the hot film probe and to identify persistent issues in the rig for future investigation. Preliminary classification of the rotor flow field was discussed in an analysis of the downstream velocity. The raw unsteady data signal was also analyzed statistically through the use of Fourier Transform and autocorrelation analysis. Experiments consisted of three types of tests: the first consisted of a horizontal 1D linear traverse, meant to act as a baseline axisymmetric case. The second test consisted of a 2D strip traverse, intended to characterize the flow behavior over a rotationally symmetric section of the downstream plane. The third test consisted of an unsteady traverse measurement, meant to record the flow over a long sampling time for signal analysis using Fourier Transform and autocorrelation analysis. The experiments showed promising results and a high potential for adding more complexity, such as a simulated tailboom in the downstream flow field. Flow characterization of averaged wake data showed a flow field consistent with published theoretical aerodynamic results. Signal analysis of instantaneous data showed a good ability for the hot film probe to distinguish periodic occurrences such as blade passing events from noise. Comparison with 7-hole pressure probe data, completed in a parallel study showed good correlation. The two measurement methods were found to complement each probe's shortcomings well. Since this analysis was as an initial test, persistent problems in the rotor rig, including frame vibration or recirculation effects occurred. Potential solutions are discussed for future investigation.