A Discontinuity-Capturing Methodology for Two-Phase Inviscid Compressible Flow

The explicit filtering approach is applied to the quasi-conservative five-equation model of compressible two-phase flows to capture the interface between each fluid and a shock wave. The basic idea of the present filter is to combine a low-order linear filter with a high-order one via a proper discontinuity sensor and optimum linear weights. The capability of the proposed filter in capturing the contact discontinuity and damping the grid-to-grid oscillations is analysed. Various one-dimensional and two-dimensional test cases are performed, namely the interface advection of gas-gas flow, the shockinterface interaction, the gas-liquid Riemann problem, and the inviscid shock-bubble interaction. The numerical results reveal that the present filtering method can accurately capture the propagation of the shock waves and interfaces. Additionally, it produces less spurious oscillations compared with the existing 2nd-order discontinuity-capturing filter

A Two-Dimensional Numerical Investigation of Aerodynamic Noise from an Inclined Plate

Direct computations of acoustic noise of flow over an inclined plate are performed at two Mach numbers by solving the compressible Navier--Stokes equations without invoking any form of modelling. The flat plate has a sharp leading edge and sharp trailing edge and is inclined at incidence of 20°. The simulations are performed at a chord-based Reynolds number of 1000, and the freestream Mach numbers of 0.4 and 0.6. The numerical results reveal the effect of the Mach number on both of the hydrodynamic near-field and the acoustic far-field. Increasing the Mach number results in an increase in the shedding frequency and a decrease in the acoustic wavelength. The directivity plots show that additional lobes are present on the plate suction side at higher Mach number

A numerical study of impulsively generated vortices between non-deformable stress-free layers

A wake behind an unsteady moving submerged vehicle is of interest and importance in a broad variety of engineering disciplines, ranging from underwater to aeronautical engineering. When the vehicle changes its speed or direction, under certain conditions, it can lead to the appearance of a coherent kilometre-scale quasi-planar counter-rotating vortical structure which persists for the order of days. The aims of this work are to determine the conditions under which such a large coherent vortex can appear and to obtain deeper understanding of its dynamics by investigating the evolution of a turbulent patch created by either an impulsively accelerating axisymmetric self propelled body or an impulsive jet in the small-scale upper ocean via direct numerical simulation. A non-conservative body force is applied to the governing equations to represent an impulsive jet, while an accelerating motion of a self-propelled body is emulated by the combination of an immersed boundary method and the body force. Criteria for the occurrence of a vortex dipole are found to depend on a dimensionless parameter, called the confinement number. Once the confinement number is higher than about unity, the vertical growth of an impulsively generated turbulent patch is restricted by the top and bottom layers of the upper ocean leading to the formation of a vortex dipole at the free surface. The contrast and strength of a surface signature increase linearly with increasing confinement number. The late-time dynamical structures, i.e. the propagation velocity, size and the decay rate of maximum vorticity, of the dipolar eddy induced by the presence of vertical confinement can be predicted by scaling laws relevant to a stratified fluid, even though the dipole possesses a Reynolds-number dependence

A numerical investigation of impulsively generated vortical structures in deep and shallow fluid layers

The evolution and formation of large-scale turbulent coherent structures induced by an impulsive jet between non-deformable stress-free layers are investigated via direct numerical simulation at a jet Reynolds number of 1250. The ratio of the initial size of the vortex to the domain depth is varied to study the influence of the bounding surface confinement. A non-conservative body force is applied to the governing equations to represent the momentum source. During the forcing period, the coherent structure appears in the form of a leading vortex ring together with a trailing jet, and breaks down to turbulence due to an instability very similar to the Widnall instability before interacting with the free surface. The input parameters (the momentum flux J, the forcing period ?t f , and the domain depth h) can be grouped together as the confinement number C = J 1/2?t f /h 2 to parameterise the intensity and strength of the eddy signature at the free surface. Increasing the confinement number corresponds to reducing the ratio of the domain depth to the initial size of the vortex, which leads to a linear increase in the maximum amplitude of the surface signature in terms of the surface eddy strength. A dipole forms for values of C greater than about unity, even though the eddy signature appears at the free surface for all the confinement numbers considere

Numerical study of turbulent manoeuvring-body wakes: interaction with a non-deformable free surface

Direct numerical simulation (DNS) is used to investigate the development of a turbulent wake created by an impulsively accelerating axisymmetric self-propelled body below a non-deformable free surface. The manoeuvring body is represented by the combination of an immersed boundary method and a body force. The Reynolds number based on either the diameter of the virtual body or the jet forcing intensity is relatively high (O(1000)), corresponding to the fully turbulent case. The vertical growth of the coherent structure behind the body is restricted by the upper and lower stress-free layers, and the wake signatures are observed to penetrate to the free surface. The late-time behaviour of the dipole induced due to vertical confinement can be predicted by scaling laws, also relevant to a stratified fluid