characteristics of the thermal spread and mixing in such jets in crossflow. The flow behaviour and heat transfer analysis of a heated jet in crossflow are reported by several researchers (for example by Wark and Foss, 1998, Chen and Hwang, 1991, Sherif and Pletcher, 1991, Nishiyama et al., 1993, Sarkar and Bose, 1995, Hwang and Chiang, 1995, Shi et al., 2003 and Said et al., 2003).
Even though extensive studies have been carried out in the past few decades to investigate the problem of jets in crossflow, some aspects of the flow requires a more detailed investigation. These aspects are in terms of resolving the flow physics, the effects of the geometry of nozzle and dimensions of the flow field etc. One of these aspects is the jet in a narrow channel crossflow and this is the subject of the present investigation.
ratios is performed. This flow configuration corresponds to the experimental work of Ramaprian and Haniu (1983) and Haniu and Ramaprian (1989). The present topic is unique due to several reasons. Firstly the jet discharge slot spans more than 55% of the crossflow duct width, rather than issuing into a semi-infinite crossflow. Thus the jet is confined in the spanwise direction. Secondly the velocity ratio is quite high (R = 6 and 9). Thirdly the flow configuration of a slightly heated jet (a temperature difference of about 60C between the jet and crossflow) is investigated. Also, the effect of streamline curvature is studied by using the standard k-ε model and its curvature modification for a preliminary 2D investigation. Besides k-ε model, Reynolds stress transport model is also used to investigate the 3D flow field of rectangular jets in crossflow, which is not reported in the literature. This type of flow configuration is encountered in a variety of different industrial processes, used to mix two product streams.
To obtain results in a simple and economical way, an investigation of the 2D flow field is done as a first step. The 2D investigation corresponds to the flow field at the central plane of the jet slot (z/D = 0, Fig. 1.1). The flow field obviously contains streamline curvature and therefore a modification to the standard k-ε model to account for the effects of the streamline curvature proposed by Cheng and Farokhi (1992) is considered. This model is relatively simple and computationally economical compared to the more advanced ways to treat turbulence, such as the use of a Reynolds stress transport (RST) model, LES or DNS. As mentioned earlier the standard k-ε model is also employed to study the turbulence characteristics of the 2D flow field. A computer code is developed in FORTRAN 77 to solve the governing 2D Reynolds-Averaged Navier-Stokes (RANS) equations numerically, using the finite volume method and SIMPLE (Patnakar, 1980) algorithm. From the investigation of 2D flow field, several important details of reasonable accuracy of the flow field in the central plane of the jet are obtained for two values of the velocity ratio (R = 6 and 9).
To extract information of the flow field in the spanwise direction a 3D investigation is necessary. A finite volume computer code is developed in FORTRAN 77 on a non- uniform staggered grid arrangement using the SIMPLE algorithm (Patankar, 1980) to investigate the 3D flow field. This code not only can give those details that a 2D code cannot give, but also is expected to give more physically realistic results in the central plane itself. The standard k-ε model is used to treat fluid turbulence in this code.
In the final phase, an investigation of a slightly heated jet in a cold crossflow is performed. The effect of buoyancy is neglected as the heating is small and the temperature is assumed to be playing the role of a passive scalar only. This computation is carried out with the commercial code FLUENT 6.2. A Reynolds stress transport (RST) model is employed to resolve the turbulence of the flow field. The different terms of the Reynolds stress transport equations that require modelling are modelled by carefully studying different proposals in the literature and selecting the ones that are thought to be the most suitable for the present flow configuration.
To put it more succinctly - the present work is concerned with the development of computational tools i.e. computer codes for 2D and 3D turbulent flows on one side and use of different turbulence models in predicting the flow field of rectangular jets in crossflow to assess their relative strengths and weaknesses on the other. Also studied are effects of streamline curvature on different flow parameters and characteristics. Influence of the relative strength of the jet discharge to that of the crossflow (R = 6 and 9) on the flow characteristics is another area that is investigated.
Overall a detailed qualitative and quantitative description of the flow field is provided with exhaustive illustrations. In the study of the slightly heated jet, the temperature variation in the flow field is investigated.
The dispersion of the temperature in all three directions is studied. The structurally interesting phenomena of the formation of different types of vortices in the flow field and their characteristics are studied. Their effects on the velocity and temperature fields are also discussed. The ability of the turbulence models in capturing those different types of vortices is discussed. The distinct flow features due to the relatively narrow passage between the sidewalls are also described by discussing the qualitative differences of the present observations from those of jets in semi-confined or unconfined crossflow reported in the literature. Also the drawbacks of the 2D predictions are reported by making a comparison of 2D and 3D predictions with the experimental data. Wherever possible, the predictions are validated by careful comparison with established results.