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Wavelet-based optical flow velocimetry (wOFV) is used to estimate two-dimensional velocity fields from tracer particle images acquired simultaneously with CH PLIF imaging within two highly turbulent premixed methane-air flames. Unlike conventional correlation-based PIV approaches, the current wOFV approach yields a dense (i.e. one vector per pixel) estimation of the velocity field which offers the possibility of greatly enhanced spatial resolution as compared to correlation-based PIV. Results from the wOFV method and correlation-based PIV are directly compared in terms of instantaneous fields, flow statistics, energy spectra, and derived gradient quantities such as vorticity and 2D strain rate. An assessment of the results indicates an increase in spatial resolution and dynamic range of almost one order-of-magnitude when using wOFV as compared to high-resolution PIV. In fact, the use of wOFV permits resolution of the smallest dissipative scales within the premixed flames with turbulent Reynolds numbers of O(104). A particular focus concerns velocity measurements near and within the CH layers, which are excellent markers of the local flame front but are spatially narrow and intermittent. The high-resolution velocity results from the wOFV method provide an opportunity for improved velocity estimations, derivative quantities, and their statistical characterization at and near the flame front. |
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