Abstract
This study presents an approach for obtaining full-field dynamic surface-pressure reconstructions with low differential amplitudes. The method is demonstrated in a setup where an air jet is impinging on a flat plate. Deformations of the flat plate under dynamic loading of the impinging jet were obtained using a deflectometry setup that allows measurement of surface slopes with high accuracy and sensitivity. The measured slope information was then used as input for the virtual fields method to reconstruct pressure. Pressure fluctuations with amplitudes of down to {mathcal {O}}(1)~text {Pa} were extracted from time-resolved deflectometry data using temporal band-pass filters. Pressure transducer measurements allowed comparisons of the results with an established measurement technique. Even though the identified uncertainties in fluctuations were found to be as large as 50%, the spatial distributions of dynamic pressure events were captured well. Dynamic mode decomposition was used to identify relevant spatial information that correspond to specific frequencies. These dynamically important spatio-temporal events could be observed despite their low differential amplitudes. Finally, the limitations of the proposed pressure determination method and strategies for future improvements are discussed.Graphic abstract
Highlights
The measurement of dynamic surface pressure distributions is crucial for a range of applications in fluid dynamics, material design and testing, as well as for the investigation of impinging jets for heat and mass transfer
Since this study aims at identifying dynamic events which are governed by the primary vortices impinging on the specimen, a circular load distribution with a peak amplitude of 10 Pa was chosen as model input, see Fig. 7a
The corresponding standard deviations, sp, obtained from these maps allowed a first evaluation of the captured pressure fluctuations
Summary
The measurement of dynamic surface pressure distributions is crucial for a range of applications in fluid dynamics, material design and testing, as well as for the investigation of impinging jets for heat and mass transfer. Microphones have high sensitivities for differential pressure amplitudes of (1) Pa and well below, depending on the type of microphone and experimental noise sources, but they allow only point-wise measurements. Fitting these microphones requires drill-holes in the investigated specimen, which change the material response. The spatial resolution may be increased using pinhole-mounting, e.g., (Robin et al 2012; Van Blitterswyk and Rocha 2017). This requires a large amount of sensors when measuring pressure over even a moderately large area. Using phase averaging in combination with proper orthogonal decomposition to measure the interaction between a rotor wake and a cylinder, PSP measurements of fluctuations within 100 Pa were achieved
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