Measuring Vortex-Induced Vibration with Hot Wire in Wind Tunnel
Long cantilever stings that support aerodynamic models in wind tunnels are a potential source of vibration problems which would damage test data quality, many documents use the methods of setting acceleration sensors on model to measure vibration of model-sting system, but setting sensors on little scale model is hard to realize, and sensors could interfere with flow field around the model. For purpose of reducing flow field interference, a method of hot wire probe measuring wake to acquire vibration parameters of model is tried, this way is easy to realize for little scale model. At the same time, methods of accelerator signal frequency domain filtering and frequency domain integration are used to acquire vibration model parameters of model-sting for comparison with data of hot wire, this method could improve the SNR of effective signal. Using method of accelerator signal power spectrum analysis, three order vibration frequencies of 31.1Hz¡¢120.9 Hz and 221.4Hz of the system are acquired. Using method of frequency domain filtering and frequency domain integration, the vibration mode and node of the system are acquired. Using method of hot wire measuring wake, vortex shedding frequencies of 31.1Hz and 124.1 Hz, and the model buffet boundary are acquired. Experiment results show that, the method of hot wire measuring model wake vortex shedding frequency for analysis of aircraft model vibration, is convenient for little scale model test, is a practical method for vortex-induced vibration measurement.
Effects of Active Sting Damping on Common Research Model Data Quality
Recent tests using the Common Research Model (CRM) at the Langley National Transonic Facility (NTF) and the Ames 11-foot Transonic Wind Tunnel (11’ TWT) produced large sets of data that have been used to examine the effects of active damping on transonic tunnel aerodynamic data quality. In particular, large statistically significant sets of repeat data demonstrate that the active damping system had no apparent effect on drag, lift and pitching moment repeatability during warm testing conditions, while simultaneously enabling aerodynamic data to be obtained post stall. A small set of cryogenic (high Reynolds number) repeat data was obtained at the NTF and again showed a negligible effect on data repeatability. However, due to a degradation of control power in the active damping system cryogenically, the ability to obtain test data post-stall was not achieved during cryogenic testing. Additionally, comparisons of data repeatability between NTF and 11-ft TWT CRM data led to further (warm) testing at the NTF which demonstrated that for a modest increase in data sampling time, a 2-3 factor improvement in drag, and pitching moment repeatability was readily achieved not related with the active damping system.
Results From a Sting Whip Correction Verification Test at the Langley 16-Foot Transonic Tunnel
In recent years, great strides have been made toward correcting the largest error in inertial Angle of Attack (AoA) measurements in wind tunnel models. This error source is commonly referred to as 'sting whip' and is caused by aerodynamically induced forces imparting dynamics on sting-mounted models. These aerodynamic forces cause the model to whip through an arc section in the pitch and/or yaw planes, thus generating a centrifugal acceleration and creating a bias error in the AoA measurement. It has been shown that, under certain conditions, this induced AoA error can be greater than one third of a degree. An error of this magnitude far exceeds the target AoA goal of 0.01 deg established at NASA Langley Research Center (LaRC) and elsewhere. New sting whip correction techniques being developed at LaRC are able to measure and reduce this sting whip error by an order of magnitude. With this increase of accuracy, the 0.01 deg AoA target is achievable under all but the most severe conditions.