At the 2015 ASME Turbo Expo in Montreal, we presented a paper on unsteady three-dimensional wet-steam flow simulations for the last three stages of a low-pressure real steam turbine. We then focused on the investigation of unsteady wetness in the three-stage blade passages, which was conducted by assuming the same number of blades in the previous study and the real blade number. The obtained results showed that wetness is definitively influenced by the blade number difference between the stator and the rotor. This paper presents a numerical investigation of unsteady pressure forces on the multi-stage blade rows caused by stator-rotor interactions, which include unsteady wakes, vortices, shocks, and wetness. In particular, we investigate the effect of blade number variation on the pressure forces. Our results indicate that unsteady pressure forces are significantly influenced by shocks from the upstream stator trailing edges transferred to the adjacent rotor blade noses. We finally found that the unsteady pressure forces on the rotor blades are strongly influenced by shocks from upstream stator trailing edges near the hub region and the forces result in a time-dependent torque difference between neighboring two rotor blades.

Unsteady three-dimensional wet-steam flows through stator–rotor blade rows in the final three stages of a low-pressure steam turbine, taking the blade number into consideration, are numerically investigated. In ASME Turbo Expo 2014, we presented the numerical results of the unsteady flow assuming the same blade number. Here, this previous study is extended to flow simulations using the real blade number. The flows under three flow conditions, with and without condensation and considering the same and real blade numbers are simulated, and the numerical results are compared with each other and with the experimental results. Finally, the effect of the blade number on unsteady wet-steam flows in real low-pressure steam turbines is discussed.

The causal relationship between unsteady forces of wet-steam flows on rotor-blade rows and the steam condensation in low pressure steam turbines is still one of unresolved issues. In this study, we investigate the effect of condensation on the time-dependent torque of final-stage long-rotor blade rows in a low pressure steam turbine. Then we simulate unsteady wet-steam flows through the three-stage stator-rotor blade rows in the steam turbine while changing the inlet temperature condition. The variation of the inlet temperature results in creating a flow field with a different amount of wetness due to condensation. The temperature and pressure in the flow field obtained from a different inlet temperature are compared with each other, and the torques calculated from the time-dependent pressure on a final-stage long-rotor blade are also relatively compared. The calculated results in this study indicate that the time-dependent torques on the final-stage long-rotor blade significantly depend on the latent heat added by condensation and that the amount of condensation is highly sensitive to variations in the inlet temperature. This study also suggests that an optimal inlet temperature may be exist for optimizing the torque of low pressure steam turbines.

No abstract

A numerical method for compressible flows with nonequilibrium condensation is reconstructed for simulating supercritical CO2 flows with nonequilibrium condensation under high pressure conditions. Thermophysical properties are interpolated from pressure-temperature look-up tables and density-internal energy look-up tables, which are generated using the polynomial equations in REFPROP. We employ the high pressure nonequilibrium condensation model in which the critical radius of a liquid droplet is modified by considering non-ideal gas. We simulate high pressure CO2 flows through a Laval nozzle, which was experimentally investigated by Lettieri et al. High-pressure CO2 passes through the nozzle, leading to a decrease in its pressure and temperature. It reaches the supercooled condition near the throat. Nucleation and the subsequent growth of droplets lead to an increase in the condensate mass fraction in the diverging area. The proposed method for real gas reproduced the peak of pressure distribution owing to the release of latent heat, whereas the numerical result assuming ideal gas is different from the experimental result. The nucleation region obtained using the present method is earlier and narrower than that in the case of ideal gas. The early and rapid nucleation leads to the high mass condensate rate at the outlet. These results show that considering the real gas effect and nonequilibrium condensation is crucial for developing the impeller of a compressor for the supercritical CO2 Brayton cycle.