Volume 36, Issue 3 -

Different strut-cavity configurations and fuel injection patterns employed in a round supersonic combustor are numerically investigated. A new parameter defined as an ideal nozzle outlet velocity is used to evaluate performances of different strut-cavity configurations and fuel injection patterns. This parameter is a reflection of the contribution of the combustor performance to the engine thrust. The peak of the velocity curve stands for the best performance of the combustor. Then the flowfields are discussed in detail. The flow structures indicate that the injection from the wall behind a strut achieves a great penetration because of the strong upward transport that results from the streamwise vortices behind the strut. Results show that the combustor performance and the flowfields are greatly influenced by the fuel injection patterns. The fuel injections from the strut sides and from the center ring achieve the better performances than that from the wall behind the struts.

The influence of nozzle clearance on the flow field for a variable nozzle turbine, and moreover on the turbine stage performance was numerically investigated. Meanwhile, unsteady calculations were also performed to capture the shock waves which were induced by excessive acceleration of the exhaust gas. Aiming at improving the turbine stage performance and mitigating the shock waves, a forepart rotation vane was proposed and investigated in this work. The results indicated that by using the forepart rotation vane, the stage efficiency is increased by 6 % and the shock waves were eliminated successfully at small nozzle openings. Additionally, the intensity of pressure fluctuation that acts on the rotor blades was reduced by mitigation of clearance leakage flow and shock waves, which is beneficial for the reliability of rotor blades.

The purpose of this study is to optimize the 1st stage of the transonic high pressure turbine (HPT) for enhancement of aerodynamic performance. Isentropic total-to-total efficiency is designated as the objective function. Since the isentropic efficiency can be improved through modifying the geometry of vane and rotor blade, lean angle and sweep angle are chosen as design variables, which can effectively alter the blade geometry. The sensitivities of each design variable are investigated by applying lean and sweep angles to the base nozzle and rotor, respectively. The design space is also determined based on the results of the parametric study. For the design of experiment (DoE), Optimal Latin Hypercube sampling is adopted, so that 25 evenly distributed samples are selected on the design space. Sequentially, based on the values from the CFD calculation, Kriging surrogate model is constructed and refined using Expected Improvement (EI). With the converged surrogate model, optimum solution is sought by using the Genetic Algorithm. As a result, the efficiency of optimum turbine 1st stage is increased by 1.07 % point compared to that of the base turbine 1st stage. Also, the blade loading, pressure distribution, static entropy, shock structure, and secondary flow are thoroughly discussed.

In aero-engine combustor, the primary and secondary dilution air jets play a vital role to achieve efficient combustion and provide a satisfactory temperature profile at the combustor exit. In the current research, seven kinds of three-dome combustor sector associated with different dilution holes arrangements are simulated using Flamelet model. The influences of location, number and diameter of dilution air holes on flow field and performance of combustor are analysed in detail. The results demonstrate that the variation of airflow distribution, while keeping the total admission area constant, impact the combustion efficiency and pattern profile considerably, yet has insignificant effect on the total pressure coefficient. The maximum combustion efficiency and minimum pattern factor can be achieved simultaneously with deliberate dilution jet holes arrangement.

The term sustainability became a popular subject both in the automotive industries and in the aerospace industries. Increasing and threatening environmental pollution problems and reduction in limited fuel sources are motivating either industries and academicians to develop alternative power systems to sustain more healthier and economical life in the long term. One innovation that has been researched in the automotive industry is all electric and hybrid electric propulsion concepts. These concepts have also been proposed as alternative solutions for aviation. These novel propulsion technologies are composed of a gas turbine/internal combustion engine structure (necessary for hybrid electric and turboelectric propulsion systems) and/or energy storage components (battery, fuel cell and so on.) with multiple electric motors respectively. In this paper, simulation of a high fidelity turboshaft engine-alternator model for turboelectric propulsion system is derived. To develop an aero-thermal engine model, GE T700 turboshaft engine data is used and constructed model is connected to an alternator model on MATLAB/Simulink environment. Open-loop simulations are carried out and satisfactory results are obtained.Simulation results are compared to the real engine design point data. Results show that there are acceptable differences between the simulation results and the real engine data. The power balances between compressor - high pressure turbine and power turbine – alternator are proven in the mathematical model. It is expected that the proposed model can be easily extended to power system design and power management studies in turboelectric propulsion systems and also in other suitable novel propulsion systems.

This paper presents a performance evaluation of non-axisymmetric casing grooves combined with airflow injection in a transonic axial compressor with NASA Rotor 37, using three-dimensional Reynolds-averaged Navier-Stokes equations with the k-ε turbulence model. An axisymmetric casing groove was divided circumferentially into 36 non-axisymmetric grooves. The numerical results for adiabatic efficiency and total pressure ratio were validated with experimental data. A parametric study for stall margin, stable range extension, peak adiabatic efficiency, and total pressure ratio at peak adiabatic efficiency of the compressor was performed using five parameters: the front and rear lengths, the height of the casing groove, the injection mass flow rate, and the injection angle. The non-axisymmetric casing grooves combined with injection improve greatly the stall margin and stable range extension of the transonic axial compressor, but reduce only slightly the peak adiabatic efficiency in all cases, compared to the results for a smooth casing.

The application of radial and axial-centrifugal compressors in turboprop, turboshaft and turbofan engines may require the construction of small diameters diffuser in order to obtain lower weight and smaller frontal area. Conventional exhaust diffusers typically have large outlet diameters for exit Mach numbers lower than 0,2 and low swirl flow to the combustor, hence the design of channel of the low-diameter diffusers called controlled-contour, fishtail-shaped diffuser or diffusing trumpet is complex. The cross-sectional shape of these channels is varied from circular to oval to elliptic and to rectangular. The paper presents an original method for determining the flow parameters in the channel and at the outlet section of the downstream diffusing trumpet for a pipe diffuser, which constitutes the downstream duct of the radial or axial-centrifugal compressor with the pipe diffuser. It also illustrates a new method for determining the geometrical parameters of the diffuser. Mentioned methods (for conceptual design of a compressor with pipe diffuser) are based on Pythagorean theorem, properties of ellipse, equation of continuity, energy equation, first law of thermodynamics, Euler’s moment of momentum equation, gasdynamics functions and definitions used in theory of turbo-machines.

A conventional and advanced exergy analysis of a turbofan engine is presented in this paper. In this framework, the main exergy parameters of the engine components are introduced while the exergy destruction rates within the engine components are split into endogenous/exogenous and avoidable/unavoidable parts. Also, the mutual interdependencies among the components of the engine and realistic improvement potentials depending on operating conditions are acquired through the analysis. As a result of the study, the exergy efficiency values of the engine are determined to be 25.7 % for actual condition, 27.55 % for unavoidable condition and 30.54 % for theoretical contion, repectively. The system has low improvement potential because the unavoidable exergy destruction rate is 90 %. The relationships between the components are relatively weak since the endogenous exergy destruction is 73 %. Finally, it may be concluded that the low pressure compressor, the high pressure compressor, the fan, the low pressure compressor, the high pressure compressor and the combustion chamber of the engine should be focused on according to the results obtained.

In order to improve product development cycle, design engineers use multidisciplinary analysis tools which allow for better productivity. This paper covers the development of new tools to improve the preliminary design phase of turbine disc, being a critical part of aircraft engines. First, a new single platform D&A (Design & Analysis) tool integrating commercial CAD (Computer Aided Design) and FEA (Finite Element Analysis) software processing in batch mode is presented. This integrated architecture leads to a real improvement, enabling a cohesive single integrated simulation environment that offers significant time reduction on user manipulation and execution. An optimization of disc geometry is then performed by using different optimization algorithms and configurations for a given disc parameterized model. The results show potential improvement over the current preliminary rotor discs for life and burst limited design. Finally, optimal curves obtained by developing HPT (High Pressure Turbine) disc reference charts, indicate how to get the minimum weight for given mechanical performance without running any structural analysis. These new tools supporting disc design have allowed improvement of disc life and durability leading to a reduction of preliminary design phase duration.

In the present study, the mechanical behaviors and microstructural evolution of the nickel-based superalloy FGH97 at different temperatures and strain rates were studied. First, the tensile tests were conducted at temperatures of 20 °C, 450 °C and 700 °C, respectively, at two specified strain rates of 0.00025 s –1 and 0.001 s –1 . Second, the microscopic observations of the sections were carried out to analyze the microstructure feature. Based on the test data and the observations, it was found that the influence of strain rate on the deformation and elongation will be weakened at higher temperature. Furthermore, the phenomenon of stress serrations and the intermedia temperature brittleness were just observed at 450 °C, and the reason for that was investigated.