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Title: Optimisation techniques for combustor wall cooling
Author: Krawciw, Jason
ISNI:       0000 0004 7971 0098
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2017
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In a drive to increase the thermal efficiency of modern gas turbine engines, the turbine entry temperature (TET) has been steadily increasing over time to the point where the hot gasses contained within the combustion chamber have temperatures well in excess of the melting point of the materials used in its construction. As a result compressor exit air is widely used to cool these components. However, the use of this air is detrimental to the cycle efficiency. Therefore an important area of study is in optimising the use of this cooling flow in order to minimise the amount of air diverted from the main cycle. Effusion cooling techniques involving the use of a number of holes arrayed on the combustor liner wall are widely used and with additive manufacturing techniques such as direct laser deposition (DLD) gaining maturity, the design space of the cooling passages has become much wider. Therefore methods of assessing the performance of these newly enabled designs must be developed. This thesis describes a number of methodologies used to evaluate the performance of effusion cooling systems. Experimental methods are employed to determine both overall effectiveness using infrared (IR) thermography and adiabatic film effectiveness using pressure sensitive paint (PSP) and the heat-mass transfer analogy. These measurement techniques are carried out using a single near-ambient conditions wind tunnel and a single set of metal test plates. These methods are used to determine the relative performance of six coolant passage geometries ranging from a simple cylindrical angled effusion design to more exotic helical flow passages. Computational techniques are also used to evaluate the relative film performance of the same six geometries utilising a simplification technique which splits the effusion calculation up and uses a single-passage computation to determine the through-hole flow field then extracts flow properties on a plane near the passage exit. These data are then used as boundary conditions for the effusion array, reducing the mesh size dramatically as only a small region near each hole exit is included in the computation. A conjugate simulation is also carried out on the single-passage geometry to investigate the heat transferred through the passage walls. These techniques are used to investigate the performance of the six cooling geometries at various conditions of liner pressure drop and freestream turbulence levels. The PSP tests indicate that increasing the momentum ratio beyond 6 has little effect on the adiabatic effectiveness performance for the majority of the designs considered, the only exception being a design which utilises densely packed rows of cooling slots while increasing the distance xii between successive rows. These tests also indicated that the main effect of increasing freestream bulk turbulence is to increase the turbulent mixing, resulting in wider coolant traces in the lateral direction while reducing the streamwise trace length. Sensitivity to bulk turbulence levels generally decreases with increasing momentum ratio. IR thermography shows that overall effectiveness is sensitive to freestream turbulence levels with higher turbulence levels showing reduced overall effectiveness for all plates tested. The increased coolant flow associated with higher momentum ratio results in increased overall effectiveness. The computational model struggles to predict the absolute levels of adiabatic film effectiveness accurately. However, the model does show good agreement with experimental data in terms of ranking the six designs tested, with the six designs falling into three main performance bands. The datum cylindrical angled effusion design shows the lowest performance levels in terms of overall and adiabatic effectiveness, with the straight fanned geometries showing significant improvements over the datum. The two helical geometries showed the highest performance of the designs tested combining a strong film with improved internal heat transfer characteristics.
Supervisor: Not available Sponsor: Rolls-Royce
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Engineering not elsewhere classified ; Film cooling ; Effusion cooling ; Pressure sensitive paint ; Infrared thermography ; CFD