Investigators: Professor Tom Povey

Students: Ben Kirollos, Salvador Luque

Sponsors: Rolls-Royce Turbines

The thermal performance of cooling systems for high-pressure nozzle guide vanes (HPNGVs) is typically assessed at engine conditions using a thermal-paint-test engine as part of the engine certification process. Such tests are generally restricted to final qualification of cooling systems before production. Promising cooling systems with some element of design risk (lower TRL) would not normally be tested in engine products. This extends the time required for new technology to enter service engines.

The continuing maturation of metal laser-sintering technology (DMLS) and the ability to reproduce thermal-paint test conditions in the laboratory environment presents two opportunities: firstly supplementing thermal paint test engines to de-risk the engine design process with additional tests during the engine development programme; and secondly the chance to test promising designs of lower TRL to accelerate the rate at which technology is transitioned from research into engine products.

The Annular Sector Heat Transfer Facility (Sector Facility) at the University of Oxford, operates using engine-realistic geometry, and at correct M, Re and coolant-to-mainstream pressure ratio. We have demonstrated that it is possible to assess the overall thermal performance of laser-sintered and conventionally cast parts, and to scale between the results. Using techniques developed in the facility the first openly reported thermal assessment of an entire laser-sintered vane at sufficiently engine-realistic conditions to support the use of laser-sintered components as a developmental tool within the design optimisation process has been presented.

A number of promising next-generation cooling systems have previously been investigated and developed in the Sector Facility, e.g., dendritic cooling systems [1] and reverse-pass cooling systems based on the ideas in [2]. The facility has also been used to conduct comprehensive parametric studies, of, for example, coolant mass flow rate.

[1] Luque, S., Batstone, J., Gillespie, D.R.H., Povey, T., and Romero, E., 2014, “Full Thermal Experimental Assessment of a Dendritic Turbine Vane Cooling Scheme,” 136.

[2] Kirollos, B., and Povey, T., 2014, “Reverse-Pass Cooling Systems for Improved Performance,” Journal of Turbomachinery, 136.

[3] Kirollos, B., Povey, T., 2017, “Method for Accurately Evaluating Flow Capacity of Individual Film-Cooling Rows of Engine Components” ASME Journal of Turbomachinery, Vol. 139, 111004, doi: 10.1115/1.4037028.

The group also performs theoretical work on cooling system optimisation ([4], [5])

4] Kirollos, B., Povey, T., 2016, “Cooling Optimization Theory—Part I: Optimum Wall Temperature, Coolant Exit Temperature, and the Effect of Wall/Film Properties on Performance,” ASME. J. Turbomach., 138(8):081002-081002-12. doi:10.1115/1.4032612.

[5] Kirollos, B., Povey, T., 2016, “Cooling Optimization Theory—Part II: Optimum Internal Heat Transfer Coefficient Distribution,” ASME. J. Turbomach., 138(8):081003-081003-15. doi:10.1115/1.4032613.

Earlier work on the development of techniques in the facility can be found here ([6], [7]):

[6] Luque, S., and Povey, T., 2011, “A Novel Technique for Assessing Turbine Cooling System Performance,” Journal of Turbomachinery, 133.

[7] Luque, S., Aubry, J., and Povey, T., 2009, “A New Engine-Parts Annular Sector Cascade to Prove NGV Cooling Systems,” 8th European Conference on Turbomachinery, Fluid Dynamics and Thermodynamics, Verlag der Technischen Universtat Graz, Graz, Austrai, March 23-27, pp.865-878.

Figure 1. 2d unwrapped schematic of working section in the sector facility.
Figure 2. SS and PS overall cooling effectiveness for cast and laser-sintered vanes, normalised by maximum cast vane overall cooling effectiveness.