7,114 research outputs found
High-resolution simulations and modeling of reshocked single-mode Richtmyer-Meshkov instability: Comparison to experimental data and to amplitude growth model predictions
The reshocked single-mode Richtmyer-Meshkov instability is simulated in two spatial dimensions using the fifth- and ninth-order weighted essentially nonoscillatory shock-capturing method with uniform spatial resolution of 256 points per initial perturbation wavelength. The initial conditions and computational domain are modeled after the single-mode, Mach 1.21 air(acetone)/SF6 shock tube experiment of Collins and Jacobs [J. Fluid Mech. 464, 113 (2002)]. The simulation densities are shown to be in very good agreement with the corrected experimental planar laser-induced fluorescence images at selected times before reshock of the evolving interface. Analytical, semianalytical, and phenomenological linear and nonlinear, impulsive, perturbation, and potential flow models for single-mode Richtmyer-Meshkov unstable perturbation growth are summarized. The simulation amplitudes are shown to be in very good agreement with the experimental data and with the predictions of linear amplitude growth models for small times, and with those of nonlinear amplitude growth models at later times up to the time at which the driver-based expansion in the experiment (but not present in the simulations or models) expands the layer before reshock. The qualitative and quantitative differences between the fifth- and ninth-order simulation results are discussed. Using a local and global quantitative metric, the prediction of the Zhang and Sohn [Phys. Fluids 9, 1106 (1997)] nonlinear Padé model is shown to be in best overall agreement with the simulation amplitudes before reshock. The sensitivity of the amplitude growth model predictions to the initial growth rate from linear instability theory, the post-shock Atwood number and amplitude, and the velocity jump due to the passage of the shock through the interface is also investigated numerically
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Influence of diesel fuel viscosity on cavitating throttle flow simulations at erosive operation conditions
This work investigates the effect of liquid fuel viscosity, as specific by the European Committee for Standardization 2009 (European Norm) for all automotive fuels, on the predicted cavitating flow in micro-orifice flows. The wide range of viscosities allowed, leads to a significant variation of orifice nominal Reynolds numbers for the same pressure drop across the orifice. This in turn, is found to affect flow detachment, formation of large-scale vortices and micro-scale turbulence. A pressure-based compressible solver is used on the filtered Navier-Stokes equations using the multi-fluid approach; separate velocity fields are solved for each phase that share a common pressure. The rates of evaporation and condensation are evaluated with a simplified model based on the Rayleigh-Plesset equation; the Coherent Structure Model is adopted for the sub-grid scales modeling in the momentum conservation equation. The test case simulated is a well reported benchmark throttled flow channel geometry, referred to as ’I-channel’; this has allowed for easy optical access for which flow visualization and LIF measurements allowed for validation of the developed methodology. Despite its simplicity, the Ichannel geometry is found to reproduce the most characteristic flow features prevailing in high-speed flows realized in cavitating fuel injectors. Following, the effect of liquid viscosity on integral mass flow, velocity profiles, vapor cavities distribution and pressure peaks indicating locations prone to cavitation erosion are reported
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