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.
Measurement and analysis of a gust generator flow field in wind tunnel
A pilot gust generator is as experiment object,by measuring the flow field of the gust generator in different situations with two dimension hot wire anemometer,the measurement scheme and online measuring angle correction,and the calculation of the gust amplitude and flow fluctuation are proposed.Experiment results show that online angle correction used can improve the accuracy and efficiency of two dimension hot wire in Ydirection,phase analysis used can satisfy the calculate the amplitude and fluctuation of periodic gust.Gust amplitude is in direct ratio with the vane oscillation frequency of 4~15Hz,oscillation angle of 8°~30°,and vane chord length of 50~100mm.Unstability(velocity fluctuation at same phase)of the gust flow has a certain linear relationship with the vane oscillation angle and wind speed,which increases while the vane oscillation angle and wind speed increase in the test range,at the same time,proper vane oscillation frequency can decrease unstability.The conclusion is helpful for the gust generator development and flow field measurement in wind tunnel.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.