A semi-implicit method for resolution of acoustic waves in low Mach number flows

Large eddy simulation of the turbulent flow past a backward-facing step with heat transfer and property variations

High-resolution viscous flow simulations at arbitrary Mach number

In many cities, ambient air quality is deteriorating leading to concerns about the health of city inhabitants. In urban areas with narrow streets surrounded by clusters of tall buildings, called street canyons, air pollution from traffic emissions and other sources may accumulate resulting in high pollutant concentrations. For various situations, including the evacuation of populated areas in the event of an accidental or deliberate release of chemical, biological and radiological agents, it is important that models should be developed that produce urban flow fields quickly. Various computational techniques have been used to calculate these flow fields, but these techniques are often computationally intensive. Most fast response models currently in use are at a disadvantage in these cases as they are unable to correlate highly heterogeneous urban structures with the diagnostic parameterizations on which they are based. In this paper, a novel variant of the popular projection method for solving the Navier–Stokes equations has been developed and applied to produce fast and reasonably accurate parallel computational fluid dynamics (CFD) solutions for flow in complex urban areas. This model, called QUIC-CFD represents an intermediate balance between fast (on the order of minutes for a several block problem) and reasonably accurate solutions. This paper details the solution procedure and validates this model for various simple and complex urban geometries.

A CFD-based wind solver for an urban fast response transport and dispersion model

We present a collocated pressure-based method for the solution of viscouslinviscid fluid flow problems incorporating compressible and incompressible regimes. The solution domain is discretized using a control-volume-based finite element method. The fully implicit method does not experience any stability difficulties due to compressibility effects at low Mach numbers. The pressure/velocity decoupling problem is fully resolved herein for flow regimes from incompressible through compressible flow. Transonic and supersonic flows are covered by including the pressure/density coupling, which arises in high-speed flows, in the continuity equation. This is done in such a manner that the continuity equation remains a constraint equation for pressure in all flow regimes. Test problems with wide variations in geometry and fluid physics have been successfully solved, demonstrating the generality and computational capability of the method. The scheme is both efficient and robust. The accuracy of the method has been checked by comparing the results with other numerical results available in the literature and with the exact solution.

Pressure-based control-volume finite element method for flow at all speeds

The properties of a preconditioned, coupled, strongly implicit finite difference scheme for solving the compressible Navier-Stokes equations in primitive variables are investigated for two unsteady flows at low speeds, namely the impulsively started driven cavity and the startup of pipe flow. For the shear-driven cavity flow, the computational effort was observed to be nearly independent of Mach number, especially at the low end of the range considered. This Mach number independence was also observed for steady pipe flow calculations; however, rather different conclusions were drawn for the unsteady calculations. In the pressure-driven pipe startup problem, the compressibility of the fluid began to significantly influence the physics of the flow development at quite low Mach numbers. The present scheme was observed to produce the expected characteristics of completely incompressible flow when the Mach number was set at very low values. Good agreement with incompressible results available in the literature was observed.

On solving the compressible Navier-Stokes equations for unsteady flows at very low Mach numbers

The properties of a preconditioned, coupled, strongly implicit finite-difference scheme for solving the compressible Navier-Stokes equations in primitive variables are investigated for two unsteady flows at low speeds, namely the impulsively started driven cavity and the startup of pipe flow. For the shear-driven cavity flow, the computational effort was observed to be nearly independent of Mach number, especially at the low end of the range considered. This Mach number independence was also observed for steady pipe flow calculations; however, rather different conclusions were drawn for the unsteady calculations. In the pressure-driven pipe startup problem, the compressibility of the fluid began to significantly influence the physics of the flow development at quite low Mach numbers. The present scheme was observed to produce the expected characteristics of completely incompressible flow when the Mach number was set at very low values. Good agreement with incompressible results available in the literature was observed.

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K.-H. Chen

Papers

On solving the compressible Navier-Stokes equations for unsteady flows at very low Mach numbers

On solving the compressible Navier-Stokes equations for unsteady flows at very low Mach numbers

On solving the compressible Navier-Stokes equations for unsteady flows at very low Mach numbers