Effect of structure parameters of the flow guide vane on cold flow characteristics in trapped vortex combustor

The cold flow characteristics are investigated to show the effect of the structural parameters of the flow guide vane on the trapped vortex combustor（TVC）. The results show that the structural parameters have significant effects on the TVC. As a/ H increases, the total pressure loss, the wall shear stress at the bottom of the cavity and the turbulent intensity in the main combustion zone increase. b/ B does not have a significant effect on the cavity flow structure and the total pressure loss, and the wall shear stress at the bottom of the cavity increases as b/ B increases. There is no significant increase of the turbulent intensity with the increase of b/ B. The increase of c/ L has little effect on the total pressure loss, and it is not conducive to a stable combustion. As c/ L increases, the wall shear stress at the bottom of the cavity decreases. When a/ H= 0.4, b/ B= 0.4, c/ L= 0.1, a desirable dual-vortex structure is formed with an acceptable pressure loss to achieve a stable combustion. Moreover, to ascertain that the flame is stable for different values of Vm a with the optimal structural parameters, the effect of Vm a on the flow field is discussed. Results suggest that the dual-vortex structure has no relationship with the increase of Vm a. Furthermore, an unsteady simulation is conducted to show the generation and the development of the dual-vortex.

Transient simulation of a pump-turbine with misaligned guide vanes during turbine model start-up

Experimental studies of a model pump-turbine S-curve characteristics and its improvement by misaligned guide vanes （MGV） were extended to prototype pump turbine through 3-D transient flow simulations. The unsteady Reynolds-averaged Navier-Stokes equations with the SST turbulence model were used to model the transient flow within the entire flow passage of a reversible pump-turbine with and without misaligned guide vanes during turbine model start-up. The unstable S-curve and its improvement by using misaligned guide vane were verified by model test and simulation. The transient flow calculations were used to clarify the variations of pressure pulse and internal flow behavior in the entire flow passage. The use of misaligned guide vanes can eliminate the S-curve characteristics of a pump-turbine, and can significantly increase the pressure pulse amplitude in the entire flow passage and the runner radial forces during start-up. The MGV only decreased the pulse amplitude on the guide vane suction side when the rotating speed was less than 50% rated speed. The hydraulic reason is that the MGV dramatically changed the flow patterns inside the entire flow passage, and destroyed the symmetry of the flow distribution inside the guide vane and runner.