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Presented is a simulation of an engine cylinder head undergoing water quenching process using a recently developed approach for modeling quenching cooling of metal parts (Wang et al., 2002). The approach is based on the AVL SWIFT Eulerian two-fluid method with special emphasis on handling high mass exchange rate associated with quenching. A tetrahedral grid of 830,000 cells is generated for the computational domain, which includes the solid part of the cylinder head immersed in the fluid. Detailed vapor and temperature distributions are obtained which offer valuable information for the thermal stress analysis. It is observed that the temperature field within the cylinder head is highly non-uniform. The computed cylinder head monitoring point temperature versus time is compared with that registered by the thermal couple measurement. Reasonable agreement is observed. The simulation exercise may potentially be used to identify the cause of cracks often encountered in quenching heat treatment thereby lead to a better design of the process.

Presented are two approaches for coupled simulations of the injector flow with spray formation. In the first approach the two-fluid model is used within the injector for the cavitating flow. A primary breakup model is then applied at the nozzle orifice where it is coupled with the standard discrete droplet model. In the second approach the Eulerian multi-fluid model is applied for both the nozzle and spray regions. The developed primary breakup model, used in both approaches, is based on locally resolved properties of the cavitating nozzle flow across the orifice cross section. The model provides the initial droplet size and velocity distribution for the droplet parcels released from the surface of a coherent liquid core. The major feature of the predictions obtained with the model is a remarkable asymmetry of the spray. This asymmetry is in agreement with the recent observations at Chalmers University where they performed experiments using a transparent model scaled-up injector. The described model has been implemented into AVL FIRE computational fluid dynamics code which was used to obtain all the presented results.

SUMMARYThe paper presents an e cient ÿnite volume method for unstructured grids with rotating sliding parts composed of arbitrary polyhedral elements for both single-and two-phase ows. Mathematical model used in computations is based on the ensemble averaged conservation equations. These equations are solved for each phase and in case of single-phase ow reduce to the transient Reynolds-averaged Navier-Stokes (TRANS) equations. Transient ow induced by rotating impellers is thus resolved in time. The use of unstructured grids allows an easy and exible meshing for the entire ow domain. Polyhedral cell volumes are created on the arbitrary mesh interface placed between rotating and static parts. Cells within the rotating parts move each time step and the new faces are created on the arbitrary interfaces only, while the rest of the domain remain 'topologically' unchanged. Implicit discretization scheme allows a wide range of time-step sizes, which further reduce the computational e ort. Special attention is given to the interpolation practices used for the reconstruction of the face quantities. Mass uxes are recalculated at the beginning of each time step by using an interpolation scheme, which enhances the coupling between the pressure and velocity ÿelds. The model has been implemented into the commercially available CFD code AVL SWIFT (AVL AST, SWIFT Manual 3.1, AVL List GmbH, Graz, Austria, 2002). Single-phase ow in a mixing vessel stirred by a six-bladed Rushton-type turbine and two-phase ow in aerated stirred vessel with the four-blade Rushton impeller are simulated. The results are compared with the available experimental data, and good agreement is observed. The proposed algorithm is proved to be both stable and accurate for single-phase as well as for the two-phase ows calculations.

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A numerical approach is presented for modeling quenching cooling of solid metal parts. The approach is based on the Eulerian two-fluid model with modifications toward specific needs of boiling heat transfer. Numerical aspects are discussed on handling high phase change rate of boiling, flux formulation in the presence of strong body force, and conjugate heat transfer of solid immersed in a liquid bath. The modeling approach is assessed for a quenching cooling problem with a simple geometry. Comparisons are made between the computed temperature history within the solid and that of measured data using thermocouples. Reasonably well agreement is observed. The study demonstrated that the present modeling approach is able to meet the numerical challenges entailed in quenching cooling and able to predict the quenching cooling phenomena with satisfactory accuracy. Areas for further improvement are also noted.

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