Dynamic Similarity in Turbine Deposition Testing and the Role of Pressure

Abstract

The role of absolute pressure in deposition testing is reviewed from first principles. Relevant dimensionless parameters for deposition testing are developed and dynamic similarity conditions are assessed in detail. Criteria for establishing appropriate conditions for laboratory studies of deposition are established pursuant to the similarity variables. The role of pressure is particularly singled out for consideration relative to other variables such as temperature, particle size, and test article geometry/scaling. A case study is presented for deposition in a generic array of impinging jets. A fixed quantity (2g) of 0–10micron Arizona Road Dust (ARD) is delivered to the impingement array at three different temperatures (290, 500, and 725K) and at fixed pressure ratio. Deposition results are presented for operating pressures from 1 to 15atm. Surface scans show that the height of deposit cones at the impingement sites decreases with increasing pressure at constant temperature and pressure ratio. This reduction is explained by the lower “effective” Stokes number that occurs at high particle Reynolds numbers, yielding fewer particle impacts at high pressure. A companion CFD study identifies the additional role of Reynolds number in both the impingement hole losses as well as the shear layer thickness.

Particle-Vane Interaction Probability in Gas Turbine Engines

“…Stokes number is often used to scale the boundary conditions in gas turbine component and subcomponent rig tests, such as in Ref. [7]. In this work, the authors used the original Stokes number (Eq.…”

“…The traditional form of the Stokes number however is much simpler to calculate and is more widely used, e.g., Ref. [7].…”

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

“…Some may have looked at the pressure ratio across the cooling scheme but it was exhausted to ambient and so any effect absolute pressure has on deposition is ignored. Sacco et al [13] constructed a high pressure facility to look at the independent effects that absolute pressure and temperature had on an impinging flow.…”

“…The type and size of dust used in deposition experiments are important parameters to control. The dust used in this body of work is ARD, which is a common dust used in these types of experiments [11, [13][14][15][16]21]. Since the coolant in an engine is taken from the compressor, Dunn's findings that the mass mean particle diameter in the bleed of the high pressure compressor was 6 μm indicate that particles around this size should be focused on.…”

“…The k-ω SST model with an inlet turbulence level of 1% was used. This model was chosen based on similar simulations that used the k-ω SST model[13,16,21,23,34]. The fluid geometry was meshed in Star CCM+ using an unstructured advancing layer mesher with 5 prism layers to capture the near wall region and a max wall y+ less than 1.09.…”