The Effect of Particle Size on Deposition in an Effusion Cooling Geometry

Abstract

The effect of particle size on particle accumulation within an effusion cooling geometry common to gas turbines was investigated experimentally and computationally.A flat plate with an effusion cooling hole array based on a gas turbine combustor liner was subjected to particulate laden flow in an accelerated deposition facility. The tests were conducted at an engine relevant plate temperature of 1118 K, coolant temperature of 950 K, and held at a constant pressure ratio of 1.03 (cavity to ambient). To elucidate the effect of particle size, six unique size distributions of Arizona Road Dust (ARD) smaller than 20 micron were introduced to the flow independently. Experiments were also conducted in which two different dust size distributions were sequentially delivered to the test article. These experiments clearly indicate that the smallest particles within the range tested accumulate within the hole creating deposit structures and blocking the effusion holes. They also indicate that larger particles within this range can have an erosive effect on the deposit structures as they build, changing the structure's morphology and blockage behavior.Computational fluid domains were developed to replicate the test article geometry before and after a test to investigate the effect that deposit structures have on deposition.Particles were introduced to these domains after reaching a steady solution and were tracked through the solution with a Lagrangian trajectory solver. The impact locations of iv the particles were recorded and a particle sticking model was employed to determine if the particles stick or rebound. The domain with the clean hole showed that the smallest particles impact and were prone to sticking in the area where deposits form experimentally. As the particles increase in size, the number of impacts and likelihood of sticking decreased. The domain with scoop deposit structures showed that these structures can change the particle impact trajectories influencing the buildup process.Overall, this body of work shows that particle size distribution has a first order effect on the blockage caused by particle deposition in effusion cooling geometries. The observation that 0.5-3 μm particles are primarily responsible for blockage while large particles can reduce deposit structure size highlights the complexity of particle deposition. This has significant implications for future work, particularly high fidelity modeling.v

Particle Deposition in the Vicinity of Multiple Film Cooling Holes

“…One of the challenges facing in film cooling is the deposition of particles, which are mainly originated from the pollutants, e.g., sand, debris, and ash, in inlet air or fuel, on the turbine blade [7][8][9]. These deposits can easily change the surface morphology and block the cooling holes, resulting in the deviation of the film cooling from its original design and thus degrading of the film cooling efficiency and endangering the safety of the turbine blade.…”

“…Cardwell et al [14] studied the effect of different particle blockages on the mass flow of cooling air under a specific pressure ratio. Wolff et al [9] explored the impact of particle size on the deposition on the film cooling. The results showed that the particle with smaller size was easier to deposit, but the large particle was likely to destroy the deposition.…”