Aero-thermodynamic and mechanical design of a single stage axial turbine stage has been carried out for small gas turbine engine in Propulsion Division, CSIR-NAL. From the engine design configuration extract, it is envisaged that the single stage axial gas turbine operating close to 50500 rpm and at an elevated temperature of 1095K would meet the power requirement of mixed flow compressor of 385kW. This paper presents the aero-thermodynamic, mechanical design and analysis of a single stage highly loaded axial turbine stage with a stage loading coefficient of 1.45 and a flow coefficient of 0.67. The mean-line and detailed 3D aero-thermodynamic design is carried out using commercially available dedicated turbomachinery design codes Axial® and Axcent™ of Concepts NREC. The number of blades of the rotor and stator are 50 & 19 respectively. The turbine stage has undergone a series of design improvements. The final configuration of single stage turbine is analyzed using commercially available RANS CFD software ANSYS-CFX™ and NUMECAFINE™/Turbo flow solver. The design is carried out by aiming 88% total-to-total efficiency. Detailed 3D-RANS CFD analysis of the turbine shows that, the design requirements of turbine are achieved with enhanced efficiency of 90%. Mechanical design & analysis of the turbine stage is carried out using ANSYS-Mechanical™ software. Nimonic-90 material is selected for fabrication. Detailed non-linear steady thermal-structural analysis is carried out for both stator assembly and rotor BLISK. Burst margin of rotor disk is estimated to be around 63% at design speed.

Reynolds Averaged Navier-Stokes CFD analysis is carried out for a twin spool turbine of a typical small gas turbine engine, using commercial CFD solvers by employing SST turbulence model to understand the 3D flow field. In this work, detailed performance characterization at design and off-design speeds of both the high pressure (HP) and the low pressure (LP) stages is carried out using two approaches. In the First approach, individual HP and LP turbine stages are analyzed separately (case 1) with well-defined inlet and outlet boundary conditions and, in the second approach HP and LP turbine stages are analyzed together (case 2). NUMECA-AutoGrid is used to generate a good quality mesh with y+ around one. RANS CFD simulations are carried out for design speed, using both ANSYS-CFX and NUMECA“s FINE/Turbo solver and compared for conformity of the CFD analysis results. Further ANSYS-CFX is used for the detailed flow simulations for design and off-design speeds. The turbine parameters such as mass flow function, specific work function and total-to-total adiabatic efficiency of the HP and LP turbines are compared for case 1 and case 2. From case 1 & case 2 analysis, it is observed that, LP turbine stage is capable of allowing higher mass flow than required, but HP turbine stage limits the mass flow. Cascade testing of HP turbine mean section profiles has been carried out and compared with CFD analysis results.

Increasing demands on the improvement of the performance of the turbocharged internal combustion engine places in turn higher demands on the efficiency of turbochargers. The aerodynamic performance of the turbocharger compressor is influenced by the uniformity of airflow that the impeller receives. Typically, the compressor performance is measured in a gas stand with straight and conical adaptors. The ducting before the compressor in a vehicle is invariably more complex with additional bends than in the gas stand test setup. This creates differences in performance of engine compared to the performance based on the compressor map obtained from the gas stand. In this study, Computational Fluid Dynamic (CFD) simulations are performed for a compressor with a baseline intake that has a single bend and the results are compared with the test data. Subsequently tests and CFD simulations are performed with ducts having additional bends. The CFD results provide insight into the losses arising in the intake. Additional bends and the nature of bends add to total pressure losses and distorts the flow going into the impeller. The inlet distortion and total pressure losses are quantitatively expressed in terms of a set of parameters in order to facilitate comparison of different designs. The intake geometry is modified to improve the overall compressor efficiency by reducing pressure drop and inlet distortion.

Increasingly stringent emission norms place tougher challenges on the efficiencies of a turbocharger. Higher efficiency requirement on turbocharger translates into tighter tolerances on the various geometrical dimensions. While this is applicable for all the components, in this study, the focus is on the compressor wheel. Compressor wheels are either cast or milled and variations are possible in either of the processes. Even small changes in the dimensions of compressor wheel (like diameter, angle distribution, thickness distribution, axial length and blade width etc.), cause the performance losses in Turbo charger. Loss in Performance of turbocharger affects Low-end torque, power rating, fuel economy as well as increasing compressor exit temperature. It is therefore important to understand and quantify the impact of the variation in blade geometry on pressure ratio, choke flow and efficiency. In this paper, a few case studies of manufacturing variations in blade thickness, blade height and axial length are shown based on gas stand tests as well as 3D CFD simulations. A process for extracting real geometry from white light scan data obtained from the manufactured wheel is shown which helps to compare the differences with the design intent geometry. Flow simulations with the real geometry show the impact on performance. Subsequently a systematic analysis of the variations is carried out to quantify the performance impact.

Turbocharger has a paramount influence on the performance of an internal combustion. Improved emission requirements have led to complex after treatment systems, which add pressure drop to the air management system. One of the ways to mitigate negative effects of pressure drop is to improve turbocharger efficiency. The scope of performance improvement for a typical turbocharger majorly lies on the modification of compressor wheel, turbine wheel, volutes etc. The major challenges in compressor wheel modification include setting the right major geometrical dimensions, considering compressor operability at different application requirements, design cycle time and the cost of computation. Present study is about evolving an effective optimization methodology, which comprises of parametrization of compressor stage at preliminary design stage and optimization of the chosen parameters through coupling one dimensional flow analysis tool with a robust optimization tool. The parameters were chosen based on their influence on overall efficiency and pressure ratio at different mass flows and varying engine rotational speeds. Surrogate models have been used to choose the optimal designs from the preliminary design space as per requirement and optimized designs were analyzed further for verification. Final validation has been carried out using a 3D RANS code.