科研之友
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摘要
Numerical simulations of the turbulent flow over the flat backed Ahmed model at Reynolds number Re similar or equal to 4 x 10(5) are conducted using a lattice Boltzmann solver to clarify the mean topology of the static symmetry-breaking mode of the wake. It is shown that the recirculation region is occupied by a skewed low pressure torus, whose part closest to the body is responsible for an extra low pressure imprint on the base. Shedding of one-sided vortex loops is also reported, indicating global quasi-periodic dynamics in conformity with the seminal work of Grandemange et al. (J. Fluid Mech., vol. 722, 2013, pp. 51-84). Despite the limited low frequency resolution of the simulation, power spectra of the lateral velocity fluctuations at different locations corroborate the presence of this quasi- periodic mode at a Strouhal number of St = 0 : 16 +/- 0 : 03. A shallow base cavity of 5% of the body height reduces the drag coefficient by 3% but keeps the recirculating torus and its interaction with the base mostly unchanged. The drag reduction lies in a global constant positive shift of the base pressure distribution. For a deep base cavity of 33% of the body height, a drag reduction of 9 : 5% is obtained. It is accompanied by a large elongation of the recirculation inside the cavity that considerably attenuates the low pressure sources therein together with a symmetrization of the low pressure torus. The global quasi- periodic mode is found to be inhibited by the cavity.
- 出版日期2017-11
- 单位中国地震局
