Summary |
The behaviour of a jet discharged in the middle of a long line of jets in a coflowing environment is modeled using a hybrid approach. The hybrid approach combines the integral and length-scale approaches to model the dispersion of a jet in a coflowing environment. Typical of a length-scale model, the jet's behaviour is divided into a number of distinct regimes in which a single parameter (formed from a combination of the governing parameters) dominates the behaviour of a jet. In this situation it is the initial excess momentum, ambient velocity and the port spacing that govern the behaviour of the jet. Length-scales can be formed by combining the dominant parameters in each regime and these length-scales represent the order of magnitude of the location of the transition between the flow regimes. In each regime the behaviour of the jet is modeled with the analytical solution of a relatively sirnple integral model. At the transition between the flow regimes the excess momentum and tracer fluxes of the integral jet solutions are matched. The advantage of this hybrid approach is that it enables the development of a relatively simple solution of a complex problem which retains the flexibility of a length-scale model, but the use of integral solutions reduces the dependence of the model on empirical information. The hybrid model predicts the velocity decay, radial growth and dilution of a jet as it moves downstream from the source and merges with its neighbors in a coflowing environment. A hybrid model has been developed using the FORTRAN programming language and it is given the name "JET". Predictions from JET have been compared with the full integral model solution for a merging jet in a coflow which was developed by Davidson (1989). Beyond the transition zone, the hybrid model fits the reference integral model well. At the transition zone, the hybrid model has an abrupt change between the different flow regimes and this introduces errors into the predictions. However, these errors can be reduced with an appropriate choice of length-scale constants. |