The advantages of labyrinth-honeycomb seals in turbomachines are widely increasing the usage of them. In this investigation, a numerical study has been done to simulate a labyrinth-honeycomb seal which is commonly used in rotor blade tip. Three-dimensional simulation has been performed by ANSYS-CFX. Simulation results show good agreements with experimental data. To have better understanding of flow behavior within the labyrinth-honeycomb seal, a set of sensitivity analyses on geometry parameters has been carried out. First, a smooth plate has been replaced with honeycomb and sensitivity analyses on geometry parameters have been performed. Then the sensitivity analyses of full model with honeycomb on the geometry parameters are done. The sensitivity analysis is done on: (i) gap between labyrinth and smooth plate or honeycomb, (ii) thickness of labyrinth fins, (iii) height of labyrinth fins, (iv) height of honeycomb cells (only for the honeycomb model), and (v) the effect of different fin thicknesses and their combinations. The results show that as the height of labyrinth rises, there would be much more vortices in the flow field and consequently the overall loss would increase and mass flow rate decreases. In addition, the width of labyrinth fins in small gaps has an important role on the mass flow rate. In small gaps, as the width of labyrinth fin decreases, the mass flow of smooth model decreases, but the mass flow of honeycomb model increases. Furthermore, in large gaps, the existence of smooth plate or honeycomb has minor influence on the flow field. In addition, larger cell depth of honeycombs leads to increasing loss. In this paper, a model with straightforward labyrinth is also investigated and the results have been compared with the stepped labyrinth.

No abstract

During transonic flow of steam in divergence nozzles, flow first supercools and then nucleates to become two-phase droplet flow. This phenomenon especially occurs in the last stages of steam turbines and affects performance. In this research, a numerical scheme for two-phase flow in nozzle passages is developed. An Eulerian-Eulerian reference frame is used for both phases. The shear stress transport turbulence model is used to model the Reynolds stresses appearing in the averaged Navier-Stokes equations. The homogeneous nucleation model is applied for the mass transfer in the transonic conditions. In this paper three nozzles with different rate of expansion are employed to be under study. Overall pressure ratio (static to total pressure) and droplet size are compared with the experimental data and good agreements are observed.