Numerical simulation and passive control of condensing flow through turbine blade by NVD Method Using Eulerian-Lagrangian Model

摘要

The nucleation phenomenon and its consequence formation of droplets are destructive effects that occur as a result of the sudden expansion of the flow through the steam turbine blades. The formation of these droplets causes blade corrosion and severe thermodynamic losses, thereby reducing the turbine efficiencyg. In this paper, two holes on the pressure and suction surfaces of the turbine blade were improvised in order to control and optimize the turbine performance. These holes transfer the steam from the high-pressure to the low-pressure part of the cascade; accordingly, the steam is moved from within the cascade itself without using the external steam. For this purpose, an in-house code is written in two-dimensional, compressible, viscous, and turbulent, based on Navier-Stokes equations. To simulate the turbulent flow, the k-k(L)-omega turbulence model is used. The governing equations of the dry flow are solved by the Eulerian approach using a semi-implicit density-based method. Also, in order to avoid the oscillations caused by high accuracy numerical solution, a limiter method called Normalized Variable Diagram (NVD) is employed. For the wet part of the solution field, the equations corresponding to the Lagrangian form are solved. To validate the present numerical code, the results are compared with the experimental data and good agreement is obtained. The results showed that as the hole inlet comes to close the leading edge, further improvement is achieved. Constructing the holes on the suction and pressure surfaces in the case where the holes inlet were closer to the leading edge resulted in complete removal of the wetness from suction and pressure surfaces, and on the middle passage at the outlet of the turbine blade was reduced by 6.7% compared to the baseline geometry. The droplet radius size at the turbine blade outlet on the suction, pressure and mid-pass surface decreased by 99%, 95%, and 29%, respectively, compared to the baseline geometry. Since the hole construction is a passive flow control method without the need to consume energy, using this method to control wet steam is an optimal method. (C) 2020 Elsevier Ltd. All rights reserved.