Abstract
This experimental study explored the dynamics of lock-in phenomena associated with upstream shear layer (USL) instabilities for an equidensity gaseous jet in crossflow (JICF). Axisymmetric sinusoidal forcing of the jet fluid at different forcing amplitudes and frequencies was used to explore lock-in under flow conditions corresponding to naturally occurring absolutely/globally unstable and convectively/locally unstable shear layers, at relatively low and high jet-to-crossflow momentum flux ratios , respectively. Dynamical phenomena were quantified via hotwire anemometry, which not only documented differences in spectral characteristics but also in Poincaré maps obtained via time-delay embedding in the temporal data. The experiments provided evidence of unconditional lock-in as well as quasiperiodicity in response to forcing, reflective of marginal lock-in phenomena; these phenomena were observed for both globally unstable and convectively/locally unstable shear layers in the absence of forcing. The free jet limit in the absence of crossflow also exhibited unconditional lock-in, with some characteristics similar to those for the JICF at applied forcing frequencies above the fundamental mode. For the globally unstable JICF, a simple van der Pol nonlinear oscillator model used to represent the dynamics of the USL showed consistency with experimental findings and thus provided additional insights into the nature of shear layer dynamics.
5 More- Received 10 July 2019
DOI:https://doi.org/10.1103/PhysRevFluids.5.013901
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