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SUMMARYWithin the framework of the pressure-based algorithm, an artificial compressibility method is developed on a non-orthogonal grid for incompressible and low Mach number fluid flow problems, using cellcentered finite-volume approximation. Resorting to the traditional pseudo-compressibility concept, the continuity constraint is perturbed by the time derivative of pressure, the physical relevance of which is to invoke matrix preconditionings. The approach provokes density perturbations, assisting the transformation between primitive and conservative variables. A dual-dissipation scheme for the pressure-velocity coupling is contrived, which has the expediences of greater flexibility and increased accuracy in a way similar to the monotone upstream-centered schemes for conservation laws approach. To account for the flow directionality in the upwinding, a rotational matrix is introduced to evaluate the convective flux. Numerical experiments in reference to a few well-documented laminar flows demonstrate that the entire contrivance expedites enhanced robustness and improved overall damping properties of the factored pseudo-time integration procedure.

SUMMARYIn this paper Roe's flux-difference splitting is applied for the solution of Reynolds-averaged Navier-Stokes equations. Turbulence is modelled using a low-Reynolds number form of the k-c tubulence model. The coupling between the turbulence kinetic energy equation and the inviscid part of the flow equations is taken into account. The equations are solved with a diagonally dominant alternating direction implicit (DDADI) factorized implicit time integration method. A multigrid algorithm is used to accelerate the convergence. To improve the stability some modifications are needed in comparison with the application of an algebraic turbulence model. The developed method is applied to three different test cases. These cases show the efficiency of the algorithm, but the results are only marginally better than those obtained with algebraic models.

In small Rankine cycle power plants, it is advantageous to use organic media as the working fluid. A low-cost single-stage turbine design together with the high molecular weight of the fluid leads to high Mach numbers in the turbine. Turbine efficiency can be improved significantly by using an iterative design procedure based on an accurate CFD simulation of the flow. For this purpose, an existing Navier-Stokes solver is tailored for real gas, because the expansion of an organic fluid cannot be described with ideal gas equations. The proposed simulation method is applied for the calculation of supersonic flow in a turbine stator. The main contribution of the paper is to demonstrate how a typical ideal-gas CFD code can be adapted for real gases in a very general, fast, and robust manner.

In this paper we present results of delayed detached eddy simulation (DDES) and computational hydroacoustics (CHA) simulations of a marine propeller operating in a cavitation tunnel. DDES is carried out in both wetted and cavitating conditions, and we perform the investigation at several propeller loadings. CHA analyses are done for one propeller loading both in wetted and cavitating conditions. The simulations are validated against experiments conducted in the cavitation tunnel. Propeller global forces, local flow phenomena, as well as cavitation patterns are compared to the cavitation tunnel tests. Hydroacoustic sources due to the propeller are evaluated from the flow solution, and corresponding acoustic simulations utilizing an acoustic analogy are made. The propeller wake flow structures are investigated for the wetted and cavitating operating conditions, and the acoustic excitation and output of the same cases are discussed.