Browsing Department of Mechanical Engineering & the Built Environment by Subjects
Now showing items 1-4 of 4
A CFD study of twin Impinging jets in a cross-flowA very complicated three-dimensional (3D) flow field is generated beneath a Vertical/Short Take-Off and Landing (VSTOL) aircraft when it is operated near the ground. This flow field can be represented by the configuration of twin impinging jets along the spanwise direction in a cross-flow. This paper describes a Computational Fluid Dynamics (CFD) study of this flow using the Reynolds Averaged Navier-Stokes (RANS) approach with a Reynolds Stress Model (RSM). The use of an RSM potentially offers a compromise between the computational efficiency of a two equation turbulence model and accuracy closer to that of Large Eddy Simulation (LES) although it will not be as accurate as LES. The current numerical results are validated against experimental data and the mean velocity profiles are reasonably well predicted by both the standard k-ε model and the RSM with slightly better prediction by the RSM. However, the Reynolds stress prediction by the RSM is poor compared with the experimental data, indicating that to capture the detailed unsteady flow features an LES is needed.
Computational study of flow around 2D and 3D tandem bluff bodiesNumerical simulations have been carried out to advance our current understanding of flow around two dimensional (2D) and three dimensional (3D) square shaped tandem bluff bodies at a Reynolds number of 22,000, especially to shed light on the sudden change of the downstream body’s drag coefficient. The Reynolds-Averaged Navier-Stokes (RANS) approach has been employed in the present study and the predicted drag coefficients compare reasonably well with available experimental data. Better understanding of flow fields has been achieved by analyzing streamlines, velocity vectors for both 2D and 3D cases in a horizontal plane and a vertical symmetric plane. The sudden jump in drag coefficient for the 2D case is well captured numerically, which is due to the flow over the upstream body impinging onto the front face of the downstream body at a critical gap size between those two bodies. For the 3D case the drag coefficient is predicted to increase gradually, consistent with the previous experimental finding. This is due to the fact that the vortical structures formed in the 3D case are very different, resulting in a reasonably smooth change of the flow field around the upstream body and hence leading to gradual, not sudden, increase in the drag coefficient of the downstream body.
Numerical analysis of flow in the gap of a simplified tractor-trailer model with cross vortex trap deviceHeavy trucks are aerodynamically inefficient due to their un-streamlined body shapes, leading to more than of 60% engine power being required to overcome the aerodynamics drag at 60 m/hr. There are many aerodynamics drag reduction devices developed and this paper presents a study on a drag reduction device called Cross Vortex Trap Device (CVTD) deployed in the gap between the tractor and the trailer of a simplified tractor-trailer model. Numerical simulations have been carried out at Reynolds number 0.51×106 based on inlet flow velocity and height of the trailer using the Reynolds-Averaged Navier-Stokes (RANS) approach. Three different configurations of CVTD have been studied, ranging from single to three slabs, equally spaced on the front face of the trailer. Flow field around three different configurations of trap device have been analysed and presented. The results show that a maximum of 12.25% drag reduction can be achieved when a triple vortex trap device is used. Detailed flow field analysis along with pressure contours are presented to elucidate the drag reduction mechanisms of CVTD and why the triple vortex trap configuration produces the maximum drag reduction among the three configurations tested.
Numerical study of effusion cooling flow and heat transferAn isothermal and non-isothermal numerical study of effusion cooling flow and heat transfer is conducted using a Reynolds-averaged Navier–Stokes (RANS) approach. A Reynolds stress transport (RST) turbulence model is used to predict the flow field of a staggered array of 12 rows of effusion holes, each hole inclined at 30° to the flat plate. The Reynolds number based on the hole diameter and jet exit velocity is 3800. The blowing ratio in both studies is 5. A conjugate heat transfer approach is adopted in the non-isothermal simulation. For the isothermal case, the RST model is shown to be capable of predicting the injection, penetration, downstream decay and lateral mixing of the effusion jets reasonably well. In addition, the numerical model captures the existence of two counter-rotating vortices emanating from each hole, which causes the entrainment of combustor flow towards the surface of the plate at the leading edge and downstream, influences the mixing of accumulated coolant flow, providing a more uniform surface temperature across the plate. The presence and characteristics of these vortices are in good agreement with previously published research. In the non-isothermal case, the laterally averaged cooling effectiveness across the plate is under-predicted but the trend conforms to that exhibited during experimentation.