Dieter Peitsch

Numerical Investigation of Vortex Reducer Flows in the High Pressure Compressor of Modern Aeroengines

Modern jet engines require very high cycle temperatures for efficient operation. In turn, cooling air is needed for the turbine, since the materials are not yet capable of taking these temperatures. Air is taken from the compressor for the purpose of cooling and turbine rim sealing, bypassing the main combustion circuit. Since this affects the efficiency of the engine in a negative manner, measures are taken to reduce the amount of air to an absolute minimum. These measures include the investigation of reducing pressure losses within the involved subsystems. One of these subsystems in the BR700 aeroengine series of Rolls-Royce is the vortex reducer device, which delivers bleed air to the secondary air system of the engine. The German government has set up a research project, aiming for an overall improvement of aeroengines. This program, Engine 3E, where 3E reflects Efficiency, Economy and Environment, concentrates on the main components of gas turbines. Programmes for the high pressure turbine and for the combustion chamber have been set up. The high pressure compressor has been identified as key component as well. A new 9-stage compressor is being developed at Rolls-Royce Deutschland to adress the respective needs. From the point of view of the secondary air system, the vortex reducer in this component plays a major role with respect to the efficient use of cooling and sealing air. Rolls-Royce Deutschland has performed CFD studies on the performance of different vortex reducer geometries, which currently are considered for incorporation into the future engine. The results of these investigations wil be converted into more simple design rules for proper reflection of the behaviour of this system for future designs. The paper presents the set up of the geometries, the applied boundary conditions as well as the final results. To tackle the difference between a high pressure compressor rig and a typical two-shaft engine, a dedicated investigation to assess the difference between a pure high pressure core without an internal shaft and a realistic high/low pressure shaft configuration has been carried out and is included in the paper. Recommendations to improve the design with respect to minimized pressure losses will be shown as well.© 2002 ASME

Numerical Study of Hot Gas Ingestion Into an Engine Type High-Pressure Turbine Rotor-Stator Cavity

The rims of high pressure turbines in aeroengines are sealed with air via the internal air system. This sealing is required to avoid occurrence of hot gas ingestion into the rotor-stator cavities. Due to a rapid decrease of turbine disc life at higher temperatures, such ingestion would present a hazard to the integrity of the discs and subsequently to the safety of the aircraft. One of the driving factors for ingestion is the circumferential pressure variation downstream of vanes and blades due to the aerodynamic wakes. Small ingestion cavities close to the annulus are commonly used to damp down this pressure variation. Substantial ingestion into these cavities is permitted. The actual sealing of the rotor-stator cavity itself is accomplished with a secondary seal.A numerical simulation of the flow in an engine type rotor-stator cavity was carried out using a commercial CFD code. The cases studied comprise relevant features as rotor-stator and ingestion cavities, leakage across rotor blade shanks and circumferential pressure variation downstream of an NGV. The simulation was carried out at relevant engine temperatures and pressures.The paper will firstly present the effects of a variation of the rim sealing mass flow on the flow field, ingestion and temperature increase in the cavity. These results were solely gained by computational means. For validation of a new air system design, engine tests on the BR715 jet engine have been performed. The data measured in these tests not only serve for certification purposes, but also may be used as input for CFD calculations. Thus, the experimental data was the baseline for comparison with the results from the present study.© 2001 ASME

Improvement of High Pressure Turbine Air Systems by De-Swirl Nozzles

Conventional two-stage high pressure turbine (HPT) air system concepts usually are based on exclusive use of compressor delivery air to cool HPT blades and vanes and to seal the gaps between rotors and stators. This air is expensive in terms of engine efficiency, since work has been done on it from all stages of the compressor and the air is lost for the main thermodynamic engine cycle. It is also very hot, leading to strong thermal loading of the turbine material. Improvements in this area thus lead to an immediate reduction of fuel consumption and increased cycle life of the turbine discs. On static components, it is common practice to use pre-swirl nozzles in order to reduce the relative total temperature of downstream disc and blades. To feed the interstage cavity between both HPT discs, the air is transferred through the first rotor disc or drive arm. In a conventional system, the air is passed on through straight holes, thus no benefit is taken from the internal energy potential of the cooling air, where work output from the flow would lead to an immediate air temperature reduction. The advanced air system presented in this paper uses de-swirl nozzles in the rotating part to extract energy from the fluid. By this, the air temperature for the downstream static part is reduced on the one hand and in addition, the overall turbine efficiency is increased due to the contribution from the fluid. This paper will cover the effects of an air system design change from a conventional to an advanced HPT air system on the Rolls-Royce BR715 aeroengine based on numerical analysis and test data. An overview of the change to the flow field and prospect of current research programmes in this field will be given.Copyright

Modelling the Transient Behaviour of Jet Engines

Understanding the behaviour of turbomachinery components has rapidly improved during the last years. The focus has been set mainly on unsteady component characteristics such as compressor stall and combustion chamber flameout. However, modelling the whole engine during transient operation is still a major workpackage during the development process of modern jet engines.The aim of transient modelling of jet engines is the prediction of the normal engine behaviour during changes of the powersetting, but also to prove engine safeness in abnormal operation, e.g. caused by failures of the control system. Various approaches are used depending on the application purpose. For the most accurate prediction, complex synthesis programs model each component separately and iterate to match the components against each other. For customer use as well as for evaluation whether the real control software in the Electronic Engine Controller operates satisfactorily, more simple programs are derived from this, which include the engine characteristics in a more general way. This gives a very robust tool for simulation of simple transient manoeuvres as well as e.g. flameout or starting predictions.The paper will present the variety of approaches for modelling transient engine behaviour and will discuss the limitations of these. It will also include a description, how the control system of modern jet engines, the FADEC, is set up in these environments. This modelling is needed, if a realistic approach towards reliability of in service operation shall be performed. Synthesis results are given from the development process. The use of advanced modelling of the control system with dedicated tools to improve the capabilities of the whole system is highlighted. An example for this is included with regard to the scheduling of the handling bleed valve of the booster compressor. Finally, the paper will give an outlook on the future planning of the synthesis of transient engine operation within Rolls-Royce Deutschland GmbH (RRD).Copyright

Unsteady Flow Investigations and Their Recent Challenges in Compressor Design

This paper describes the relevance of unsteady flow investigations in turbomachinery and how they are included into the design process for compressors of modern aero engines. Significant work has been performed in leadership of Professor Gallus at the Institute for Jet Propulsion and Turbomachinery (IST) at the RWTH Aachen, University of Technology, Germany, in this area of interest. Selected topics of this numerical and experimental work will be shown. This academic work has of course to be made useful for application in the design process of turbomachinery, so the connection to today’s challenges is shown as well. In recent years, blisks have become a more attractive choice for design and manufacture of compressor rotors. In contrast to the earlier years, where blade flutter has enjoyed the main focus of interest, the blisk technology requires different approaches in terms of the assessment of the interaction between structure and fluid. The implementation of the flutter and forced response investigations into the design process for blisks is thus a major issue to be solved. The paper will describe, how the relevant unsteady flow phenomena are assessed. Results will be shown for a recent engine development, the high pressure compressor for the new TP400 engine for the Airbus A400M military transport aircraft. This compressor is currently designed at Rolls-Royce Deutschland (RRD).Copyright