Matthew Kovaerk, Luke Amatucci,
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Accurate prediction of aerodynamic pressures on a building is a key factor in the estimation of wind loads on the building. Since the analytical approach has limited capacity in providing pressure estimates, wind tunnel testing is widely used. The experimental approach faces a challenge: pressures on building models cannot be directly measured by pressure sensors. Rather, a tubing system connecting the model to the sensor is required. The pressure waves propagating inside a thin, circular tube distort the aerodynamic pressures on the model owing to the acoustic and visco-thermal effects due to the fluid action on the tube, As a result, pressure fluctuations measured through a tubing system experience amplitude change and phase shift that depend on the pressure fluctuations frequencies. It is therefore necessary to develop a correction procedure for converting the distorted pressures data measured by a transducer into pressures that differ insignificantly from the actual aerodynamic pressures on the model. To address this issue, we reviewed the Navier-Stokes nist-equations, thermodynamic effects, wave propagation issues, and mass and energy conservation associated with sinusoidal air motions in cylindrical tubing systems, and developed a MATLAB-based program to calibrate the amplitude change and phase lag in tubing configurations used in wind tunnel testing. To validate the requisite amplitude ratio and phase lag transfer functions an experimental device was designed and built using a function generator and a speaker. In addition, the validation accounted for phase changes due to the measuring sequence in a multi-channel pressure scanner. The results showed that the transfer functions obtained by the numerical approaches match their experimental counterparts to a remarkably close approximation. An optimized configuration of typical tubing systems was designed for minimization of tubing effects on pressure measurements.
Technical Note (NIST TN) - 1994
Calibration, optimization, pressure measurements, transfer functions, tubing system, wind tunnel experiment.