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Engine Representative Internal Cooling Knowledge and Applications

Tags: Air

State of the Art - Background

The fuel efficiency of a gas turbine used for aircraft propulsion depends on the performance of many key engine components. One of the most important is the turbine, whose efficiency has a large influence on the engine fuel consumption and, hence, its carbon dioxide emissions.

The high-pressure turbine stage must operate at high efficiency in the most hostile environment in the engine. The turbine is subject to the engine's most aggressive heat loads because the working fluid supplied to this stage is at the peak cycle temperature, and the work generation process in the turbine accelerates the flow, which results in enormous heat flows. The gas swept components are made from high temperature alloys which resist oxidation, creep and crack propagation following thermal cycling. The turbine used in civil aircraft engines are designed to operate efficiently for thousands of hours before requiring any replacement. The thermal protection systems include low conductivity coatings and tiny ducts which feed cooling air through the components. The cooling air removes heat by convection from the inner surface of the cooling passages, and this air is often then used to produce a protective layer or film of air between the hot gas and the component. As the use of external cooling mechanisms (such as film cooling) is associated with aerodynamic losses, the improvement and optimisation of internal cooling systems have been the prime focus of turbine cooling advancement over the last decade. Several technologies are used to enhance HTCs in internal passages. These devices are typically used in combination to achieve acceptable component temperatures. The most popular methods can be summarised as follows:

- Turbulence generators, such as ribs, cast into the walls of the internal passages;

- Devices, such as pin fins or pedestals, which increase both internal surface area and turbulence intensity;

- Impingement cooling;

- Application of serpentine systems that include U-bends with associated high HTCs;

- Swirling flow systems.


The goal of ERICKA is to directly contribute to reducing aircraft specific fuel consumption (SFC) with a targeted reduction of 1% in fuel consumption relative to engines currently in service. ERICKA will provide the means of improving turbine blade cooling technology, therefore improving engine efficiency. Better cooling technology enables the cooling flow to be reduced or the turbine entry temperature (TET) to be increased. The yellow circle in Figure 1 indicates the SFC of an existing engine operating with a certain TET and turbine blade cooling flow. Line a shows a new engine with increased operating temperature and line b an engine with reduced cooling flow. Both new engines have reduced SFC through better cooling technology.

The detailed understanding of turbine cooling is a key enabler in the optimisation of the turbine operation. The technology used in turbine cooling designs includes many uncertainties because of several factors:

- The difficulty of gathering experimental data from the internal cooling passages in rotating turbine blades;

- The problems associated with predicting cooling performance using computer codes. Note that Coriolis and buoyancy forces often combine to produce complex secondary flows not modelled in existing codes.

ERICKA will research the technology to make a significant progress in understanding the internal cooling of rotating turbine blade passages by:

- Gathering high quality experimental data, and

- Developing computer codes which are calibrated with these data.

Description of Work

ERICKA is composed of the following Work Packages (WPs):

WP1 Optimisation of turbine cooling system components. This WP will first provide the industrial requirements of future numerical optimisation methods, then it will apply the methods to engine representative problems and finally test the new passage shapes.

WP2 Leading edge impingement engine geometry: This will provide an experimental database for impingement systems. WP2 will also evaluate and improve the cooling performance of impingement systems for application to High Pressure turbine cooling systems.

WP3 Radial passages engine geometry: WP3 will provide an experimental database for engine representative ribbed radial geometries. The data set will enable computer methods to be evaluated and refined, leading to more accurate flow and heat transfer predictions.

WP4 U-bend and radial passage: WP4 will provide an experimental database for CFD code validation and calibration for the U-bend cooling passages of High Pressure and Low Pressure turbines.

WP5 Computational Fluid Dynamic Studies: WP5 will provide optimal Computational Fluid Dynamics (CFD) simulation methodologies for applications encountered in WP2, 3 and 4 and will compare the different simulation strategies.

WP6 Dissemination: This will disseminate and develop exploitation plans and manage IPRs.

Expected Results

1. New simulation and optimisation software will be developed to identify optimal solutions for cooling problems. The resulting geometries will be considered for experiments in each of the experimental WPs.

2. The test conditions achieved in a rotating rig will simulate all of the important dimensionless groups that determine flow and heat transfer. The application of a test facility with this capability to the study of impingement cooling and high aspect ratio radial passages is unique.

3. Measurement in internal cooling flow channels at high and low Reynolds numbers will enable the flow and heat transfer for High Pressure and Low Pressure cooling systems to be studied.

The RHR and containment (lhs) and detail of Perspex model (rhs).
The RHR and containment (lhs) and detail of Perspex model (rhs).

Figure 1 Schematic diagram indicating the benefi ts of improved cooling technology on SFC. The yellow circle is a baseline engine.
Figure 1 Schematic diagram indicating the benefi ts of improved cooling technology on SFC. The yellow circle is a baseline engine.