59694 - The Effect of Inlet Conditions on Turbine Endwall Loss
In practical applications there can be significant variation and uncertainty in the properties of the flow upstream of a blade row. This paper explores how variations in these inlet conditions can impact endwall loss in axial turbines.
A study of three cascades is performed using Computational Fluid Dynamics (CFD) coupled with classical secondary flow theory. The thickness and shape factor of the inlet boundary layer are varied, which can produce a three-fold variation in the endwall loss coefficient. It is shown that this variation is driven by changes in the kinetic energy of the secondary flow structures, which contributes a portion of the endwall loss.
A study of the underlying mechanisms shows that the inlet conditions predominantly affect the distribution of secondary vorticity within the blade passage. Modestly thick inlet boundary layers with high shape factor cause vorticity to be concentrated towards the center of the passage. This displacement reduces vorticity cancellation effects, increasing Secondary Kinetic Energy (SKE) and therefore the loss generated.
The results are generalized to produce a tool to estimate SKE in preliminary design. To illustrate the implications, it is demonstrated that the sensitivity to Aspect Ratio depends on the inlet boundary condition. The analysis highlights strategies to reduce endwall loss and minimize sensitivity to inlet conditions.
The Effect of Inlet Conditions on Turbine Endwall Loss
Paper Type
Technical Paper Publication
Description
Session: 35-01 Loss Generation & High Fidelity CFD
Paper Number: 59694
Start Time: June 10th, 2021, 09:45 AM
Presenting Author: John Coull
Authors: John Coull University of Oxford
Christopher Clark University of Cambridge