Michael Pfitzner

Secondary Air Systems in Aeroengines Employing Vortex Reducers

A secondary air system in modern aero engines is required to cool the compressor and turbine discs and make sure that no hot gas ingestion occurs into the cavities between the turbine discs, which could cause an inadvertent reduction of disc life.A high integrity solution for guiding the air from the compressor to the turbine is through an inner bleed from the compressor platform and through the space between the disc bores and the shaft connecting the fan with the low pressure turbine.Since strongly swirling air is taken from the compressor platforms to a much lower radius, a means of deswirling the air has to be used to avoid excessive pressure losses along the flow path.The paper describes a system utilizing tubeless vortex reducers to accomplish this deswirl, which are compared to a more conventional air system utilizing tubes. The working principles of both types of vortex reducer and guidelines for the design of a secondary air system using vortex reducers are explained with supporting evidence from rig tests and CFD calculations. Opportunities for the aerodynamic optimisation of the tubeless vortex reducer are elaborated and the experience gained using the system during the development of the BR700 engine is described.Copyright

Heat Transfer in Reacting Cooling Films: Part II — Modelling Near-Wall Effects in Non-Premixed Combustion With OpenFOAM

To account for heat losses near cooled walls an extension of the flamelet model is proposed based on an enthalpy defect parameter. A definition of the enthalpy defect and its transport equation is introduced. The inclusion of the enthalpy defect into the flamelet generation and the integration in terms of a probability density function for this parameter is discussed. The near wall extension is implemented into the OpenFOAM architecture and compared to ANSYS Fluent finite rate data for a testcase of a reacting laminar cooling film over a cooled flat plate. The near wall extension seems to improve the predicted heat flux compared to the original flamelet model, but profound validation was not possible due to a lack of suitable experimental or DNS data so far.Copyright

Density Ratio Effects on the Flow Field Emanating From Cylindrical Effusion and Trenched Film Cooling Holes

The present paper investigates density ratio effects on the flow field of cylindrical hole effusion and trench film cooling. An extensive parametric study of varying blowing rates (M = 1; 2; 4; 6), momentum (I = 1; 2; 8; 16) and velocity ratios (VR = 0.5; 1; 2) was carried out at three different density ratios (DR = 1.33; 1.6; 2). All cases were simulated using the realizable k-e turbulence model with enhanced wall treatment. The mainstream boundary conditions were kept constant, while the coolant mass flow and temperature were varied. Additional 2D PIV measurements in streamwise planes and planes parallel to the wall were carried out in a heated, closed loop wind tunnel with an injection of cryogenically cooled air.For constant momentum ratios, the jet core trajectories for both configurations were almost independent from the density ratio. In case of a constant blowing ratio, the jet penetration decreased with the density ratio, while it increased for a constant velocity ratio. Downstream of the trench a large recirculation zone is visible. Furthermore, cooling air is forced out of the trench in the midplane between two cooling holes.Copyright

Study of an Optimized Trench Film Cooling Configuration Using Scale Adaptive Simulation and Infrared Thermography

In the present paper, a narrow, angled trench layout is proposed and numerically optimized. In the optimization process the trench width and depth as well as the edge contour were varied. For each design, the optimizer automatically created the geometry and a structured hexahedral mesh. Then, six blowing ratios from M = 1 to 6 were evaluated based on RANS computations. The spatial average and the standard deviation of the film cooling effectiveness served as objective variables for the optimizer. One novel configuration was studied in more detail and compared to a trench with a depth of 0.75 hole diameters D and a cooling hole angle of α = 30 deg. For both configurations unsteady simulations using the hybrid SAS turbulence model were carried out and validated against infrared thermography measurements of the adiabatic film cooling effectiveness. The match between SAS and experiment is improved compared to RANS computations with the realizable k-e-model. The optimized configuration yields a significant improvement of the film cooling performance. The swept shape of the trench promotes the lateral spreading of the coolant, while the decreased trench width reduces the mixing of cooling air and hot free-stream gas in the region between the cooling holes.© 2014 ASME

Computer Based Optimisation and Automation of Analysis and Design Processes in Aero Engine Development

Many variants of designs of different engine components have to be analysed in detail during the design and subsequent optimisation of modern aero engines. This often involves repetitive tasks and even today this process still contains a considerable amount of manual work for the majority of the tasks in the design process. Experts from different technical disciplines are involved and several different analysis tools are used. An automation of this process not only saves a lot of time during the design phase; it also increases the quality of the design since many more design variants can be screened. In the present paper the integration of different analysis codes and optimisation tools into an automated process using off-the-shelf software is described. A mix of commercial and in-house codes is integrated in a loose coupling way. Several applications from different areas of aero engine design are described. It is shown that in all cases the computer based optimisation and the process automation yields results of equal or better technical quality compared to the original hand optimised ones or improves the understanding of the design space. In addition, the necessary wall-clock time to reach the results was in all cases a fraction of that of the manual process.© 2002 ASME

Aerodynamic Optimisation of an Aeroengine Bypass Duct OGV-Pylon Configuration

In a core-mounted high-bypass aero engine the fairing around the mount arm carrying the engine weight through the bypass duct has to be designed such that the aerodynamic losses induced by this thick structure are minimized to avoid an increase of specific fuel consumption. On the other hand, the overall engine length and weight needs to be kept to a minimum so that there is no negative impact on airplane payload. This paper describes the development of an automated 2-D CFD analysis procedure for fast investigation of aerodynamic losses generated in the fan outlet guide vanes (OGV’s) and the bypass duct by the introduction of a core mount arm. Design rules for the positioning and aerodynamic form of the mount arm fairing are presented. Different configurations are compared with respect to the pressure loss induced in the bypass duct and the additional contribution to fan back pressure. A combination of well adapted aerodynamic mount arm fairing and re-staggering of the struts is presented, which only marginally increases the overall total pressure loss in the bypass duct and has negligible effect on the fan backpressure distribution.Copyright

Heat Transfer Measurements Downstream of Trenched Film Cooling Holes Using a Novel Optical Two-Layer Measurement Technique

A new approach for steady state heat transfer measurements is proposed. Temperature distributions are measured at the surface and a defined depth inside the wall to provide boundary conditions for a three-dimensional heat flux calculation. The practical application of the technique is demonstrated by employing a superposition method to measure heat transfer and film cooling effectiveness downstream of two different 0.75D deep narrow trench geometries and cylindrical holes. Compared to the cylindrical holes, both trench geometries lead to an augmentation of the heat transfer coefficient supposedly caused by the highly turbulent attached cooling film emanating from the trenches. Areas of high heat transfer are visible, where recirculation bubbles or large amounts of coolant are expected. Increasing the density ratio from 1.33 to 1.60 led to a slight reduction of the heat transfer coefficient and an increased cooling effectiveness. Both trenches provide a net heat flux reduction superior to that of cylindrical holes, especially at the highest momentum flux ratios.Copyright

Numerical and Experimental Investigation of the Film Cooling Effectiveness and Temperature Fields Behind a Novel Trench Configuration at High Blowing Ratio

The present study is a numerical and an experimental investigation of film cooling from cylindrical holes embedded in a 0.75D deep transverse trench. Additionally, a new design with tetrahedral elements located upstream of the trench was examined. They interact with the approaching boundary layer and modify the flow field near the trench. Different heights of the tetrahedrons were considered. Results from all geometries were compared to those from a cylindrical hole. The experiments were performed in a heated closed loop wind tunnel with a coolant supply at cryogenic temperatures. The adiabatic film cooling effectiveness was obtained using infrared thermography. Temperatures within the flow field were measured using a cold-wire. The experiments were performed at four blowing ratios (1.0, 2.0, 3.0 and 4.0) and two density ratios (1.19 and 1.75). CFD simulations using FLUENT were carried out in order to investigate the developing flow field. The results show that the cooling effectiveness of the trench configuration increases with increasing blowing ratio. The coolant film remains attached to the surface even at the highest blowing ratio. In comparison to the original trench configuration the adiabatic effectiveness is enhanced by the tetrahedral elements due to reduced mixing of coolant and hot gas within the trench and improved lateral spreading of cooling air. The variation of the density ratio showed that the measurements can not be scaled with the blowing ratio alone without considering the density ratio.© 2012 ASME