PIV studies of coherent structures generated at the end of a stack of parallel plates in a standing wave acoustic field

Abstract

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Application of laser-based instrumentation for measurement of time-resolved temperature and velocity fields in the thermoacoustic system

“…Very complex flow patterns occur due to the cross-sectional discontinuities at the end of stack and heat exchanger [3], which…”

“…Secondly, HWA offers relatively high temporal resolution of the acquired signal. For example, in the already mentioned work by Mao et al [3] hot wire anemometry was used to detect velocity fluctuations related to vortex shedding phenomena behind thermoacoustic stacks, which allowed obtaining reliable Strouhal number characteristics. Thirdly, the typical wire diameter of hot-wire probe is of the order of 5 m, which can potentially deliver high spatial resolution if fine stepper motor controls can be deployed (about an order of magnitude better than the LDA and PIV methods discussed below).…”

Investigation into the Strouhal numbers associated with vortex shedding from parallel-plate thermoacoustic stacks in oscillatory flow conditions

“…Referring back to the key question highlighted at the end of section 1, it seems there is a relatively smooth change of St vs. Re over the whole Re range, not a step-change (a threshold behaviour) as hypothesised in previous work based on a very fragmentary set of experiments [18].…”

“…While for stack B this dependence is practically monotonic, it is not for stacks A and C -some degree of "scatter" occurs around the underlying overall trend. However such "scattered" points can also be seen in the data obtained earlier by Mao et al [18]. It is possible that such behaviour can arise from the variability in the underlying flow patterns, as well as shedding phenomena occurring in slightly different parts of the acoustic cycle -in other words the velocity amplitude not being fully representative of the shedding phenomena, for the purpose of obtaining Strouhal number values.…”

“…In the current study, there exists a number of different flow regimes, as discussed in [23] and [24], which may be controlled not only by the peak Reynolds number itself, but also other similarity parameters such as KeuleganCarpenter number or porosity, as discussed in [18] and [20]. Nevertheless, it may be useful to present all the 76 cases studied in terms of the dependence of St vs. Re in one graph such as Figure 11 (the additional legend allows identifying the six different plate thickness values).…”