Inlet Swirl and Dump Gap Effect on Static Pressure Recov ery in Dump Diffuser Combustor u sing Two Equation Turbulence Model

Abstract

Cold flow through an axi-symmetric dump diffuser, provided with a swirl effect at inlet is studied by using various two equation k-ε turbulent models such as; standard k-ε, RNG k- ε and Realizable k-ε model. There is a liner with a liner dome head of hemispherical in shape is used as a bluff body. From the comparison in between the three k-e turbulent models, it has been observed that the overall prediction of flow variables with Realizable k-e model are much better than others. The effects of dump gap and inlet swirl on velocity distribution and pressure variation on liner and casing walls have been investigated. The static pressure recovery within the diffuser is evaluated from area weighted average pressure at inlet and exit plane. It is noticed that an optimum inlet swirl results in the most effective pressure recovery due to the minimum irrecoverable energy dissipation in the vortices formed in the domain. The optimum swirl number is found to be 0.38 and it occurs when DG (non-dimensional dump gap) is kept as 1.0. The variation in dump gap changes the flow pattern and the possible pressure recovery. As the dump gap is increased, the static pressure is recovered more effectively with moderate swirl level in the inlet flow.