Heat Transfer and Fluid Flow Analysis of a Turbulent Jet Flowing Over a Sinusoidal Wavy Surface

Abstract

The turbulent jet plays a vital role in heat transfer application and it is encountered in many practical engineering and industrial applications. The wall-bounded turbulent jets have intractable and complex flow characteristics which need more care to handle. At present, the enhancement of cooling by air jet impingement is one of the prime objectives of the industries. Exhaustive literature survey reveals that there is no study which deals with enhancement of heat transfer rate. The current study is an attempt to fill this research gap. It is well known that the heat transfer rate increases with increase in the surface area. The same concept is used in the present study and the plane wall surface is replaced by a sinusoidal wavy surface. In this work, the fluid flow and heat transfer characteristics of a turbulent jet flowing over a sinusoidal wavy surface are numerically studied. The two-dimensional Reynolds av- eraged Navier-Stokes (RANS) equations are discretized using the finite volume method. A non-orthogonal grid system with collocated variable arrangement is utilized for the solu- tion. The turbulent parameters are solved using the standard k −ε high Reynolds number turbulencemodel. The effect of sinusoidal surface and the offset ratio is studied in detail. The thesis is divided mainly into three parts. The first part discusses turbulent wall jet. The results indicate that the local Nusselt number, local heat flux and the non-dimensional maximumstreamwise velocity increase near the exit of the nozzlewhile theminimumpres- sure decreases when the amplitude of the wavy surface increases. Although, these param- eters increase near the jet exit; but, the fate of these parameters are highly dependent on the frequency and the amplitude of the wavy surface. Accordingly, a maximumincrease of 14.43%in heat transfer rate is observed for the frequency (ω) equals to 14π/L =0.58643 and amplitude equals to 0.7. In the second part, the offset jet is considered. It is noticed that the heat transfer rate de- creases in comparison to the corresponding wall jet case. Therefore, only the result of flow characteristics has been included in this chapter. It is observed that the scaled similarity solution is obtained at the crest and the trough. But, the trend is entirely different than the trend observed for the plane wall case. Also, it is found that the trend at the crest is different than the trend at the trough. These phenomena are discussed in detail. In the third part, the fluid flow and heat transfer characteristics of a turbulent dual jet are explored. The results show that the sinusoidal wavy surface affects both the flow and heat transfer characteristics significantly and also enhances the heat transfer rate. It is also noticed that not only the sinusoidal surface but also the offset ratio affects the heat trans-fer and fluid flow characteristics significantly. Based on the different combinations of fre- quency, amplitude and offset ratio, a maximum of approximately 23.27% enhancement in heat transfer rate is achieved with respect to the plane wall surface in the present case.