LES and Unsteady RANS simulations of Multiple Jet Impingement System

LES and Unsteady RANS simulations of Multiple Jet Impingement System

Penumadu, P.S.

Rao, G.A. (mentor)

Aerospace Engineering

Flight Performance and Propulsion

2015-12-11

Jet impingement is a subject of extensive research over the years due to its industrial importance and the fundamental physics of heat transfer and turbulence. These jets generate high heat transfer rates with better uniformity on the surface which is to be heated or cooled compared to other heat transfer techniques. However, to study the flow phenomenon and heat transfer rates, conducting experiments overtime for change in design has become expensive. Hence, to reduce the cost and time, the best possible way to study the jets behavior is to perform numerical simulations. With numerical simulations, one can predict the flow physics inside the domain, which is difficult to obtain from the experiments. In the recent times, there have been tremendous developments in terms of computation power and numerical models that have proved to produce good and accurate results for many applications. With these approaches, the flow characteristics can be studied in depth at each and every time step which provides better understanding about the jets behavior inside the array. However, these new models have to be tested and should be compared with experimental data to see how good these approaches can fit with the experimental results. Moreover, Large-Eddy Simulations (LES) have not been carried out in the past to investigate the flow features in an impinging jet array. So, this master thesis is focused on performing LES and Unsteady Reynolds-averaged Navier-Stokes Simulations (URANS) for multiple impinging jets and validate these CFD results with the experimental data. The primary objective of the thesis is to predict the pressure drop characteristics across the nozzles and the flow channel as the pressure drop directly affects the efficiency of the system. Simulations with Reynolds-averaged Navier-Stokes (RANS) is a good method to analyze these quantities, but it was found that through RANS approach, the results obtained from CFD simulations are over predicted than the experimental values and this deviation increases with increase in Reynolds number. So to analyze these quantities, transient simulations are performed to predict the flow physics and heat transfer characteristics. From the unsteady RANS and large eddy simulations, it was understood that the major pressure loss oc- curs inside the nozzles and due to contraction effect at the nozzle’s inlet. It was also observed that inside the nozzles the pressure drop occurs differently for the particles near the wall and particles which are in the mean flow. The pressure drop values obtained from the CFD simulations are validated with the analytical and experimental results. It was found that, the results are in good agreement with the analytical results. Fur- thermore, the heat transfer characteristics obtained from these transient simulations also show a substantial improvement compared to RANS models. The deviation in the results were found to vary between 7% - 10%. To study the effect of geometrical parameters on the heat transfer and pressure drop characteristics, a sensitivity analysis was performed by varying the nozzle to plate distance and hole diameter. It was noticed that, with the change in nozzle diameter by 10 microns, the total pressure drop of the impingement system is affected significantly. Therefore, when designing these precision systems, it is important to manufacture them accurately as, a minor change in the jet diameter would affect the system performance on a large scale. Finally, It can be concluded that, the unsteady RANS simulations would be a good approach to study the heat transfer characteristics and flow physics inside the array. However, it would be a difficult task for any turbulence model to accurately predict the pressure drop characteristics in the impinging array, as the pressure drop inside the array is extremely sensitive with the change in geometrical parameters.

LES
Jet Impingement
Unsteady RANS
CFD
Multiple jets

http://resolver.tudelft.nl/uuid:ec68055b-990a-45b5-af26-9dd67372f6d1

Student theses

master thesis

(c) 2015 Penumadu, P.S.