Frank Kocian

Materials and design concepts for high performance compressor components

Abstract High-performance compressors with increased pressure ratios require sophisticated materials solutions and design concepts. Reduced weight and increased strength and stiffness are the major requirements for highly stressed fan blades in future aircraft engines. Two different materials and design approaches will be discussed in the paper, namely local reinforcement of the titanium fan blades by using titanium matrix composites (TMCs) and by partly replacing the bulk titanium fan blade by fiber reinforced plastics (hybrid concept). While the TMCs significantly improve the mechanical properties of the fan blades, the hybrid blades can contribute to considerable weight savings. Blings (=bladed rings) offer high potential in weight savings of the entire compressor and require TMCs in particular for elevated temperature applications that are relevant in the higher stages of the compressor.

Multidisciplinary Automated Optimization strategy on a Counter Rotating Fan

Multidisciplinary automated optimization processes are nowadays essential to obtain optimal turbomachinery components. However, an extremely large number of free variables, constraints and objectives results in a complex task. This paper presents an optimization strategy developed to handle with different constraints, design goals concerning aerodynamic, mechanic and aeroelastic, and finally manufacturing aspects. This strategy has been applied to a counter rotating integrated shrouded propfan, which is developed within a DLR-project. Both rotors have been already aerodynamic optimized in a first design phase coupled with a mechanical analysis of the CF/PEEK blades with titanium clevises. Detailed analysis showed high displacements and unreliable Campbell-Diagrams. To reach a rig-ready design a new optimization strategy has been developed.The optimizations feature more than hundred free variables, two objective functions, as well as a high number of aerodynamic and mechanical constraints. The mechanical behavior of the blades has been improved step by step in four successive aeromechanical optimizations. To secure the improvement obtained in one optimization, their objective functions become constraints in the next step. In the first optimization, the efforts have been focused on reducing the maximal absolute displacements in several operation points. In the second one, the scattering of the maximal absolute displacements between several operation points have been reduced. In the third optimization, the Campbell-Diagrams have been additionally optimized. Although the aerodynamic performance remained on a good level, it decreased a little bit in this design phase. For this reason, an additional fourth optimization was performed with the objective to increase the fan efficiency by keeping the good mechanical behavior reached before.The presented optimization strategy has been successfully completed and the best members obtained show an almost satisfactory mechanical feasibility in view of the planned rig test.Copyright

Aerodynamic and Mechanical Optimization of CF/PEEK Blades of a Counter Rotating Fan

Since the development of the CRISP [1–3], a counter rotating integrated shrouded propfan, within a MTU-DLR program between 1985 and 2000, huge improvements in fan technologies have been made. In 2010 DLR launched an initiative to redesign the existing fan blades, taking advantage the latest developments in the field of material and manufacturing technology as well as numerical methods.The new fan blades will be made of a carbon fiber reinforced PEEK material. Compared to the so called “onion skin configuration” of CRISP-1m, the layers of the CRISP2 lamina setups are parallel to each other. In contrast to metals, carbon fiber reinforced plastics have an orthotropic material behavior and a higher stiffness mass ratio, which have to be taken into account. The existing shaft and bearing system of the CRISP-1m-model [1–3] will be reused. The blades are mounted in titanium clevises by bolting.To achieve an optimal design, it is necessary to optimize the aerodynamic performance together with the mechanical behavior within a multidisciplinary automated optimization process.The optimization featured approximately one hundred free design variables, two objective functions (maximal displacement for respectively Rotor 1 and Rotor 2), as well as a high number of aerodynamic and mechanical constraints (efficiency, total pressure ratio, axial Mach number, stress, strain, eigenfrequencies, etc.).This work shows how the challenge to integrate the modeling of CF/PEEK blades in a multidisciplinary design process were met in terms of the methods and optimization strategies involved. The major results of this optimization will be presented.This design approach will give a new CRISP blade design ready for a planned rig test in the axial compressor test rig at the DLR in Cologne.Copyright

Next Generation Turbine Testing at DLR

Axial turbines for aircraft engines and power plants have reached a very high level of development. Further improvements, in particular in terms of higher efficiency and reduced number of blades and stages, resulting in higher loads, are possible, but can only be achieved through a better understanding of the flow parameters and a closer connection between experiment and numerical design and simulation. An analysis of future demands from the industry and existing turbine research rigs shows that there appears a need for a powerful turbine test rig for aerodynamic experiments. This paper deals with the development and built up of a new so called Next Generation Turbine Test Facility (NG-Turb) at the German Aerospace Center (DLR) in Gottingen. The NG-Turb is a closed-circuit, continuously running facility for aerodynamic turbine investigations, allowing independent variation of engine relevant Mach and Reynolds numbers. The flow medium (dry air) is driven by a 4-stage radial gear compressor with a high pressure ratio and a wide inlet volume flow range. In a first stage the NG-Turb test section will allow investigations on single shaft turbines up to 2½ stages. In a further expansion stage the NG-Turb will be equipped with a second independent shaft system, then enabling experiments with configurations of high and low (or intermediate) pressure turbines and in particular offering the possibility for investigations at counter rotating turbines. Secondary air for cooling investigations can be provided by auxiliary screw compressors. Mass flow through the Turbine is determined redundantly with an uncertainty of about ±0.3%, using well calibrated Venturi nozzles upstream and downstream of the test section. The operation concept and main design features of the NG-Turb will be described and an overview of the applied standard measurement and data acquisition technics capturing efficiency, traverse data etc. will be given. Thermodynamic cycle calculations have been performed in order to simulate the flow circuit of the NG-Turb and to access whether turbine operating points can be driven within the performance map of the compressor system. Finally the calibration procedure for the Venturi nozzles, which has been conducted during the commissioning phase of the NG-Turb by applying a special calibration test section, is explained and some results will be shown.