Bryn N. Ubald

Leading edge instrumentation used in compressor and turbine blades for jet-engine test rigs can cause significant obstruction and lead to a marked increase in downstream pressure loss. Typical instrumentation used in such a scenario could be a Kiel-shrouded probe with either a thermocouple or pitot-static tube for temperature/pressure measurement. High fidelity analysis of a

This paper explores the use of polynomial variable projection to identify dimension reducing subspaces for stagnation temperature probes often used in turbomachinery applications. The measurement of stagnation temperature is an important performance metric in various thermal systems as it is required in the calculation of component efficiency and engine specific fuel consumption.

Leading edge instrumentation used in compressor and turbine blades for jet-engine test rigs can cause significant obstruction and lead to a marked increase in downstream pressure loss. Typical instrumentation used in such a scenario could be a Kiel-shrouded probe with either a thermocouple or pitot-static tube for temperature/pressure measurement. High fidelity analysis of a coupled blade and probe requires the generation of a high-quality mesh which can take a significant amount of an engineers time. The application of an immersed boundary method (IBM) and large eddy simulation (LES) is shown in this paper to enable the use of an extremely simple mesh to observe the primary flow features generated due to the blade and probe interaction effects, as well as quantify downstream pressure loss to within a high level of accuracy. IBM is utilized to approximately model the probe, while fully resolving the blade itself through a series of LES simulations. This method has shown to be able to capture downstream loss profiles as well as integral quantities compared to both experiment and fully wall-resolved LES without the need to spend a significant amount of time generating the ideal mesh. Additionally, it is also able to capture the turbulence anisotropy surrounding the probe and blade regions.

The measurement accuracy of the temperature/pressure probe mounted at the leading edge of a turbine/compressor blade is crucial for estimating the fuel consumption of a turbo-fan engine. Apart from the measurement error itself, the probe also introduces extra losses. This again would compromise the measurement accuracy of the overall engine efficiency. This paper utilizes high-fidelity numerical analysis to understand the complex flow around the probe and quantify the loss sources due to the interaction between the blade and its instrumentation. With the inclusion of leading-edge probes, three-dimensional flow phenomena develop, with some flow features acting in a similar manner to a jet in cross flow. The separated flow formed at the leading edge of the probe blocks a large area of the probe bleedhole, which is one of the reasons why the probe accuracy can be sensitive to Mach and Reynolds numbers. The addition of 4% free-stream turbulence is shown to have a marginal impact on the jet trajectory originated from the probe bleedhole. However, a slight reduction is observed in the size of the separation bubble formed at the leading edge of the probe, preceding the two bleedhole exits. The free-stream turbulence also has a significant impact on the size of the separation bubble near the trailing edge of the blade. With the addition of the free-stream turbulence, the loss observed within the trailing edge wake is reduced. More than 50% of the losses at the cascade exit are generated by the leading-edge probe. A breakdown of the dissipation terms from the mean flow kinetic energy equation demonstrates that the Reynolds stresses are the key terms in dissipating the counter-rotating vortex pairs with the viscous stresses responsible for the boundary layer.