No abstract

A 3D Navier-Stokes code, together with the standard k-ϵ model with wall function approach, was used to investigate the flowfield in the vicinity of three different single scaled-up film-cooling holes. The hole geometries include a cylindrical hole, a hole with laterally expanded exit, and a hole with forward-laterally expanded exit. Comparisons of numerical results with detailed flowfield measurements of mean velocity and turbulent quantities are presented for a blowing ratio and density ratio of unity. Additionally, experimental data for different blowing ratios and a density ratio of about two are taken to perform validation of the code for adiabatic film-cooling effectiveness prediction. Results show that for both the round and the expanded hole geometries the code is able to capture all dominating flow structures of this jet in crossflow problem. However, discrepancies are found when comparing the flowfield inside the hole and at the hole exit. In particular, jet location at the hole exit differs significantly from measurement for the expanded hole geometries. For the adiabatic film-cooling effectiveness, it is shown that for round and expanded hole exits the intensity of the shear regions and the source of turbulence, respectively, have a strong influence on the predictive capability of the numerical code.

Polydisperse sprays in complex three dimensional flow systems are important in many technical applications. Numerical descriptions of sprays are used to achieve a fast and accurate prediction of complex two-phase flows. The Eulerian and Lagrangian methods are two essentially different approaches for the modeling of disperse two-phase flows. Both methods have been implemented into the same CFD - package which is based on a 3D body-fitted Finite Volume method. Considering sprays represented by a small number of droplet starting conditions, the Eulerian method is clearly superior in terms of computational efficiency. However, with respect to complex polydisperse sprays, the Lagrangian technique gives a higher accuracy. In addition, Lagrangian modeling of secondary effects such as spray-wall interaction enhances the physical description of the two-phase flow. Therefore, in the present approach the Eulerian and the Lagrangian methods have been combined in a hybrid method. The Eulerian method is used to determine a preliminary solution of the two-phase flow field. Subsequently, the Lagrangian method is employed to improve the accuracy of the first solution using detailed sets of initial conditions. Consequently, this combined approach improves the overall convergence behavior of the simulation. In the final section, the advantages of each method are discussed when predicting an evaporating spray in an intake manifold of an IC-engine.

In this paper, 3D unsteady and mixing plane CFD simulations including the mainstream full stage on two tested configurations plus a third cavity geometry variance are reported. The sector models were run at test conditions and compared with the corresponding matched Network 1-D flow model to derive the sensitivity of HPT stage forward disc cavity platform axial overlap geometry and supplied purge flow to cavity ingestion dynamics. The first configuration includes no axial overlap (i.e. ΔX/ΔR = 0); the second configuration increases axial overlap by 70% (ΔX/ΔR = 1.82); the third configuration has a larger rim cavity axial spacing and a smaller platform axial overlap (i.e. ΔX/ΔR = 1.67). The unsteady and mixing plane 3D CFD models of the three configurations are run across supplied purge flows ranging from nominal to 35% of the nominal. This was done to obtain a good comparison and to justify the need for unsteady solutions in disc cavity ingestion studies. For each configuration, the CFD predicted mainstream pressure pulse decay profile inside the cavity along with absolute, relative, and static temperatures related to the amount of ingestion that mixes with the supplied flow at several radial heights in the cavity are extracted on a time-averaged and pitch-wise averaged basis. The applied CFD-Network process yields cavity sealing effectiveness versus supplied purge flow and validates platform conductance factors used in 1-D Network flow model. In particular, the unsteady CFD results for the tested configurations were able to reproduce the Network-matched rim cavity effectiveness data at the critical location more closely. The sensitivity results indicate that although, the zero overlap geometry (configuration-1) has insufficient purge flow as evident by the low upper cavity effectiveness, the amount becomes sufficient as the platform axial overlap increases for configuration-2. The influence of increasing rim cavity axial spacing (configuration-3) allows for the same effectiveness to be achieved under a smaller platform axial overlap and lower purge flow supply.

Polydisperse sprays in complex three-dimensional flow systems are important in many technical applications. Numerical descriptions of sprays are used to achieve a fast and accurate prediction of complex two-phase flows. The Eulerian and Lagrangian methods are two essentially different approaches for the modeling of disperse two-phase flows. Both methods have been implemented into the same computational fluid dynamics package which is based on a three-dimensional body-fitted finite volume method. Considering sprays represented by a small number of droplet starting conditions, the Eulerian method is clearly superior in terms of computational efficiency. However, with respect to complex polydisperse sprays, the Lagrangian technique gives a higher accuracy. In addition, Lagrangian modeling of secondary effects such as spray-wall interaction enhances the physical description of the two-phase flow. Therefore, in the present approach the Eulerian and the Lagrangian methods have been combined in a hybrid method. The Eulerian method is used to determine a preliminary solution of the two-phase flow field. Subsequently, the Lagrangian method is employed to improve the accuracy of the first solution using detailed sets of initial conditions. Consequently, this combined approach improves the overall convergence behavior of the simulation. In the final section, the advantages of each method are discussed when predicting an evaporating spray in an intake manifold of an internal combustion engine.