Annular diffusers are an integral component of the gas turbine engines of high-speed aircraft. These facilitate effective operation of the combustor by reducing the total pressure loss. The performance characteristics of these diffusers depend on their geometry and the inlet conditions. The present investigation attempts to select the range of the inlet swirl intensity for the best performance of annular diffusers with different geometries but having the same equivalent cone angle. This is analysed on the basis of the static pressure recovery and total pressure loss coefficients. The results show that the parallel diverging hub and casing annular diffuser produces the best performance at high-swirl intensities.

Investigations using computational¯uid dynamics (CFD) have been carried out on divided intake ducts having angles-of-turn as 22.58/22.58, 308/308 and 458/458 and area ratios of 2 and 3. It is observed that the core¯ow in the duct remains towards the convex walls up to the outlet plane with lower magnitudes in the centre of plane. Cross-velocity magnitudes are found to be less than 10 per cent of the longitudinal velocity at the outlet plane. Pressure recovery is found to decrease with the increase in the angle-of-turn for both area ratios.

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Investigation carried out in a plane model of a reverse-flow gas turbine combustor under isothermal flow conditions has shown that the bulk of the flow remains close to the outer liner wall between the rows of primary and dilution holes, while it shifts towards the liner mid-plane after the row of dilution holes. At the combustor outlet, the bulk of the flow remains towards the inner wall of the outlet duct, with a uniform flow distribution. At the outlet of the combustor model, turbulence intensity was approximately three times higher than that at the inlet plane.

Flow characteristics in the outer annular passage of a prototype reverse-flow combustor have been experimentally investigated and reported in this paper. Emphasis has been placed on understanding the effect of a dump gap, close to the turn-section, on the nature of flow split through various holes on the outer liner surface. Study revealed that a dump gap plays a significant role in deciding the nature of flow in the annular passage and the relative flow split. It revealed that a 2 mm dump gap gives an optimal flow split and the nature of flow at the combustor outlet. Nomenclature Psstatic pressure, N/m 2 R radial distance of measurement location, m Ri radius of inner wall at any location, m Ro radius of outer wall at any location, m Ή turbulence intensity, Vü 2 / Ua Ua axial velocity, m/s Uavi average inlet velocity, m/s Ut tangential velocity, m/s ρ air density, kg/m 3 PL ANE-I PLANE-A PLANE-B PLANE-C _L· J J 2' ± I Φ "2· 1.