Fredrik Wallin

Response Surface-Based Transition Duct Shape Optimization

Demands on improved efficiency and reduced noise levels cause a strive toward very high by-pass ratio (BPR) turbo-fan-engines resulting in large fans and small high-pressure-ratio cores. The trend of increasing the radial offset between low- and high-pressure systems has made the design of intermediate transition ducts an area of growing importance. Shape optimization techniques for turbo-machinery applications have become a powerful aero-design tool and thanks to the rapid development of computer technology, computational fluid dynamics (CFD) may be used for optimization purposes. Surrogate model-based optimization has in recent years become a good alternative to the gradient-based search algorithms. One well-known surrogate model-based approach is response surface methodology (RSM), which has been used in the present work. RSM used together with design of experiments (DOE) can be a very efficient and robust method for CFD-based optimization. Optimization of two different transition ducts has been performed and evaluated; one 2D axi-symmetric turbine duct and one 3D compressor duct. The optimization objective was to minimize the total pressure loss. For the turbine duct both a high-Re and a low-Re turbulence closure were evaluated. The influence of design space size on the turbine duct optimization was investigated and for the 3D compressor duct the effects of adding an outflow constraint were examined. It has been found that end-wall optimization has the potential to reduce duct losses significantly. An early rapid diffusion and a stream-wise curvature shift toward the outlet seem to be important mechanisms for reducing transition duct losses.Copyright

Experimental and Numerical Investigation of an Aggressive Intermediate Turbine Duct: Part 1 - Flowfield at Design Inlet Conditions

Demands on lower emissions and reduced noise levels drive the design of modern turbofan engines toward high by-pass ratios. The design of the intermediate turbine ducts, connecting the high- and low-pressure turbines, will become more important as the turbofan engine by-pass ratios are increased. In order to introduce more aggressive designs there is a need to understand the flow features of high aspect ratio and high diffusion ducts. This is part one of a two-part paper, presenting a comparison between an experimental study and a CFD analysis of the flowfield of an aggressive intermediate turbine duct for design inlet conditions. Part one focuses on the on-design conditions and the second part will focus on off-design conditions. The experimental study was performed in a large-scale, low-speed turbine facility. The work presented highlights some of the challenges associated with more aggressive intermediate ducts for the next generation of turbofan engines. The main flow features are successfully reproduced by the CFD, but there are discrepancies found in the predicted local velocity and loss levels. An explanation of the discrepancies between the experimental data and the CFD results is provided and an attempt to track the origin of these differences is made.

A Tuning-free Body-force Vortex Generator Model

The use of flow control in modern aero-design is currently an area of great interest. Vortex generators (VGs) are efficient passive flow control devices attracting interest due to their reliability and cost-effectiveness. In order to find the best possible vortex generator configuration for a specific application, computational fluid dynamics (CFD) tools are often used. However resolving such small scale devices require fine grids and time consuming computations as a consequence. A reliable VG model could shorten computational time significantly by reducing grid size and complexity. A new tuning-free body-force model has been developed and tested for a low-profile vortex generator installation in a turbine transition duct. For the case studied it has been concluded that reasonably accurate results could be obtained with a grid size reduction of up to approximately 80 by using the VG model.

Simulation of Energy Used for Vehicle Interior Climate

In recent years fuel consumption of passenger vehicles has received increasing attention by customers, the automotive industry, regulatory agencies and academia. However, some areas which affect the fuel consumption have received relatively small interest. One of these areas is the total energy used for vehicle interior climate which can have a large effect on real-world fuel consumption. Although there are several methods described in the literature for analyzing fuel consumption for parts of the climate control system, especially the Air-Condition (AC) system, the total fuel consumption including the vehicle interior climate has often been ignored, both in complete vehicle testing and simulation. The purpose of this research was to develop a model that predicts the total energy use for the vehicle interior climate. To predict the total energy use the model included sub models of the passenger compartment, the air-handling unit, the AC, the engine cooling system and the engine. Verification of the model was carried out against several complete vehicle tests using the new European driving cycle (NEDC) with different ambient temperatures ranging from −18°C to 43°C, different thermal states such as heat up or steady state and different sun loads. The agreement between simulation and measurement was demonstrated to be good for all compared properties except the compressor mechanical load. This research shows that it is possible to create a model that predicts the total energy use for vehicle interior climate for a wide range of different conditions.

Design of an Aggressive Flow-Controlled Turbine Duct

Demands on improved efficiency, reduced emissions and noise restrictions result in the need for very high by-pass ratio turbo-fan engines. Large fans and small high-pressure cores require aggressive intermediate transition ducts connecting the low-pressure and high-pressure systems. In the present work the design of an aggressive flow-controlled turbine duct is presented. A number of vortex generators are installed in a turbine duct to control the boundary layer. The objective is to suppress the existing separation and thus minimize overall duct loss. In doing so the turbine duct design space will be extended toward more aggressive configurations. By using response surface methodology, together with design of experiments based on computational fluid dynamics (CFD), an optimum flow control arrangement is determined. A vortex generator model was adopted in order to be able to investigate a large number of different configurations. The vortex generator installation is optimized with respect to vortex generator position, height, length and angle of attack.

Heat transfer investigation of an aggressive intermediate turbine duct - Part 1: Experimental investigation

In most designs of two-spool turbofan engines, intermediate turbine duct (ITD’s) are used to connect the high-pressure turbine (HPT) with the low-pressure turbine (LPT). Demands for more efficient engines with reduced emissions require more “aggressive ducts”, ducts which provide both a higher radial offset and a larger area ratio in the shortest possible length, while maintaining low pressure losses and avoiding non-uniformities in the outlet flow that might affect the performance of the downstream LPT. The work presented in this paper is part of a more comprehensive experimental and computational study of the flowfield and the heat transfer in an aggressive ITD. The main objectives of the study were to obtain an understanding of the mechanisms governing the heat transfer in ITD’s and to obtain high quality experimental data for the improvement of the CFD-based design tools. This paper consists of two parts. The first one, this one, presents and discusses the results of the experimental study. In the second part, a comparison between the experimental results and a numerical analysis is presented. The duct studied was a state-of-the-art “aggressive” design with nine thick non-turning structural struts. It was tested in a large-scale low-speed experimental facility with a single-stage HPT. In this paper measurements of the steady convective heat transfer coefficient (HTC) distribution on both endwalls and on the strut for the duct design inlet conditions are presented. The heat transfer measurement technique used is based on infrared-thermography. Part of the results of the flow measurements is also included.Copyright

Heat transfer investigation of an aggressive intermediate turbine duct: Part 2 - Numerical analysis

Demands on improved efficiency, reduced emissions and lowered noise levels result in higher by-pass ratio turbofan engines. The design of the intermediate turbine duct, connecting the high-pressure and low-pressure turbines in a two-spool engine, becomes thus more critical. The radial offset between the high-pressure core and the low-pressure system will increase, which leads to a higher aspect ratio (Δr/L) of the turbine duct. In order to improve the low-pressure turbine performance the turbine duct exit axial velocity could be reduced by increasing the duct area ratio (Aout /Ain ). In order to keep the turbine frame weight as low as possible, it is also desirable to keep the duct short, i. e. keep the non-dimensional length (L/hin ) as low as possible. Therefore, there is a need to improve the knowledge about the flowfield and heat transfer in aggressive (high aspect ratio/high area ratio) turbine ducts. The work presented here has been performed within the EU FP6 project AITEB-2, focusing on heat transfer in turbines. In a two-part paper the aerothermal behavior of a fairly aggressive intermediate turbine duct with nine non-lifting vanes has been studied. The flowfield and heat transfer data was acquired in the Chalmers Turbine Facility. The first part of the paper focuses on the experimental investigation and results. In this second part of the paper comparisons between experimental data and numerical results are made. The work highlights the challenges associated with numerical predictions of flowfield induced heat transfer in turbine ducts. The numerical analysis was performed using Chalmers in-house compressible flow solver. The experimental results are compared to CFD analyzes using two different turbulence models; k-e with wall functions and low-Re k-ω SST, and using the measured inlet conditions to the duct as boundary conditions. Previously presented flowfield comparisons showed good agreement between experiments and CFD. The main flow features, such as vorticity and pressure gradients, are reasonably well reproduced by the CFD. The heat transfer results show reasonable agreement on the hub and on the downstream part of the shroud. The heat transfer agreement is, however, poor on the shroud in the region between the duct inlet and the leading edge of the vane.Copyright