Sand Transport in a Two Pass Internal Cooling Duct With Rib Turbulators

Abstract

A two pass stationary square duct with rib turbulators subjected to sand ingestion is studied using Large Eddy Simulations (LES). Each pass has ribs on two opposite walls and aligned normal to the main flow direction. The rib pitch to rib height (P/e) is 9.28, the rib height to channel hydraulic diameter (e/Dh) is 0.0625 and calculations have been carried out for a bulk Reynolds number of 25,000. Particle sizes in the range 0.5–25 μm are considered, with the same size distribution as found in Arizona Road Dust (medium). Large Eddy Simulation (LES) with wall-model is used to model the flow and sand particles are modeled using a discrete Lagrangian framework. 220,000 particles are injected at the inlet and perfectly elastic collisions with the wall are considered. Results quantify the distribution of particle impingement density on all surfaces. Highest particle impingement density is found in the first quarter section of the second pass after the 180° turn, where the recorded impingement is more than twice that of any other region. It is also found that the average particle impingement per pitch is 28% higher in the second pass than the first pass. Results show lower particle tendency to hit the region immediately behind the rib in the first pass compared to the second pass where particle impingement is more uniform in the region between two ribs. The smooth walls do not show much particle impingement except the wall in second pass where the flow impinges after the turn. The rib face facing the flow is by far is the most susceptible to impingement and hence deposition and erosion. The results of this simulation were also compared with results obtained from experiments conducted on an identical two pass geometry with Arizona Road Dust particles. The particle impingement pattern is recorded by using a sticky tape on all surfaces to capture the particles. The numerical predictions showed good qualitative agreement with experimental measurements. These results help identifying the damage prone areas in the internal cooling passages of a turbine blade under the influence of sand ingestion. This information can help modify the geometry of the blade or location of film cooling holes to avoid hole blockage and degradation of heat transfer at the walls.Copyright © 2012 by ASME