Role of data processing in measuring temperature gradients with DOE Schardin's schlieren #2

Applications of windowed Fourier fringe analysis in optical measurement: A review

“…The measurement accuracy was shown to be higher than both the FT and the PIV mode. The WFR2 was able to detect smaller deflection angle, thus increased the measurement sensitivity [33].…”

Multi-scale approach for analyzing convective heat transfer flow in background-oriented Schlieren technique

“…The method enables local fringe processing and remedies the problems associated with the global nature of the Fourier transform. More details about the implementation and working of the WFT method for processing DOE BOS fringes are presented in [16]. For each ∆T , the relative phase between the reference and the corresponding phase modulated fringe pattern was computed using the WFT method.…”

“…The opacity of the glass is not critical; as the role of the ground glass is to act as a screen for the fringes, traditional ground glasses can be used. More details about the setup are outlined in [14], while the effects of changing the period of the fringe pattern and the distance between the test section and ground glass are discussed in [16].…”

“…Subsequently, fringe analysis methods [15] can be applied for fringe pattern demodulation or phase extraction. In a recent work [16], application of fringe analysis methods based on Fourier transform method and windowed Fourier transform (WFT) method was studied and quantitatively compared with particle image velocimetry (PIV) method [17] for flow visualization, and WFT method was shown to have superior performance with respect to other methods. Though DOE based schlieren technique offers the advantages of compactness, robustness and good measurement sensitivity, the ability to selectively investigate or visualize the heat flow features or structures on a spatial scale is lacking.…”

Quantitative flow visualization by hidden grid background oriented schlieren

“…Consequently, the role of data processing methods becomes paramount for flow visualization. Typically, data processing in BOS is performed by cross-correlation [19] but also phase extraction has been proposed [29]. Phase shifting [30,31,32] is a prominent technique for phase extraction in the domain.…”