In order to carry out experimental investigations on radial inflow gas turbine, a special test laboratory was designed and constructed at sharif University of Technology. This laboratory is introduced in the present paper and experimental procedures are elaborated on. Then, some test results are presented and discussed. The trends of performance characteristics math our expectation and show good agreement with the published research results in this field.

The work arose initially from an interest in design of radial turbine for small scale gas turbine applications typically suitable for distributed power generation system which demands compact installations. The paper describes an investigation in to the design and performance of radial inflow turbines having a capacity of 25kW at 1, 50, 000 rpm. First a non-dimensional design philosophy is deduced to design a turbine rotor. The design approach is largely one dimensional along with empirical correlations for estimating losses used to obtain the main geometric parameters of turbine. From the proposed design approach, turbine total-to-static efficiency is calculated as 84. 91% which is reasonably good. After that a modified vortex design procedure is developed to derive the non-dimensional volute geometry as a function of azimuth angle for actual flow condition. Once a specific turbine is designed, the flow is analyzed in detail using a three-dimensional Computational Fluid Dynamics (CFD) code in order to assess how accurately the performance is predicted by simple meanline analysis. Finally, a fully instrumented experimental setup is developed. The experimental investigations have been carried out to study the temperature and pressure distribution across turbine and total-to-static efficiency is calculated. The limitations of surging and choking in compressor as well as in the bearings to take up load at such high speed has allowed the tests to be conducted upto 70000 rpm only, with turbine inlet temperatures ranging from 900 K to 1000 K and a pressure ratio upto 1. 79, which developed power in the range of 1. 69 kW to 10. 22 kW. The uncertainty bands are in order of ± 13. 76% to ± 3. 12%. It is observed that the CFD results are in good agreement with test results at off design condition. CFD models over predicted total to static efficiency by order of 7-8% at lower speed. These deviations are reduced as turbine runs close to design point.

Radial inflow gas turbines are widely used in diesel engines turbochargers. They increase power and efficiency and reduce SFC in engines. The flow conditions of the turbocharger’s turbine are highly varying, due to engine exhaust. The knowledge of turbine behavior in such conditions is a basic requirement for the development of turbocharger to improve engine performance. In this paper, the performance of the radial inflow gas turbine is investigated experimentally as well as advanced one dimensional modeling. The principal equation of a flow model is the dimensionless mass flow rate equation which combines the equations of continuity, energy and entropy with modeling the losses, under steady state and full admission conditions. In this study mass flow rate, pressure ratio and efficiency are unknown, with known turbine geometry, inlet and outlet total pressure and temperature of the turbine, performance characteristics can be calculated. In one-dimensional modeling the flow passage of radial flow turbine is divided into several regions such as: inlet duct, volute, incident and rotor, and the flow is modeled in each part separately. The requirement of the analytical procedure is to predict the component discharge conditions from known inlet conditions and component geometry. The computed discharge conditions then become known inlet conditions for the next component. Incident loss at the rotor inlet is the main cause of efficiency drop under off design conditions. In practice the best efficiency occurs at optimum incident angle, so any deviation from optimum incident angle causes extra losses. Incident loss is part of the rotor loss but in this study, due to modeling strategy it is modeled separately. In this study Wallace model have been adopted to calculate the incident loss, which is assumed that for the off design condition the change in deviation of the fluid entry the turbine rotor takes place at constant pressure. This model is compared with simple NASA model, which shows improving the turbine calculated performance results. The complex, three-dimensional flow pattern in the rotor gives raise the difficulties in the rotor modeling and causes the major turbine losses happening in the rotor. The following losses are used in this section: friction losses, blade loading losses, tip clearance losses and exit velocity losses. Experimental investigation of the research is carried out on special test facility under full admission conditions for a wide range of speed. The efficiency and mass parameter characteristics of the turbine are obtained from the modeling and are compared with that of experimental results over a wide rang of speeds showing good agreements. The main limitation in experimental data is due to the compressor surge. The maximum difference between experimental and theoretical results under full admission conditions is 5.1% for mass parameter, and 7.2% for efficiency.

In this study, the radial flow turbine of a cryogenic turbine is investigated numerically and then compared with the current experimental results at different operation conditions. In this investigation, the turbine performance curve is obtained and three dimensional flow field in the turbine is analyzed. The rotor and casting geometry are modeled in BLADE GEN and CATIA software's respectively. The TURBO GRID software is used for grid generation of rotor while the ANSYS MESH software is applied for grid generation of casting. Finally, 3D numerical solution of fluid flow in the turbine is solved by CFX flow solver. In this approach, compressible flow equations are solved according to the pressure based method with SST turbulence model. To ensure the numerical results, the grid independency is studied. Numerical simmulation results show the flow is chocked through the turbine rotor. Also, the maximum turbine efficiency is equal 62 percent at flow conditions with rotational speed of 27000 rpm and mass flow rate of 0.174 kg/s. Finally, the performmance characteristics of the turbine are obtained numerically which are then compared to the experimental results. The comparison shows good agreement between numerical and experimental results, and maximum error is 7.27 perccent.

Radial force in low-head axial flow turbines (AFTs) is an influential factor in their operational stability. To explore the transient operating behavior of the radial force in low-head AFTs under different blade numbers, transient numeric computations were executed with the shear stress transport (SST) k-w turbulent model. Turbine performance was numerically computed and compared with results from experiments. Furthermore, the unsteady flow field pulsations were experimentally verified by means of pressure sensors. The radial forces on the runners (z = 2, 3, and 4) were each numerically studied in time, frequency, and joint time–frequency fields. The result reveals that the radial force acting on the runner varies with time, since periodic radial forces reflect the vane number on the stay vanes with minimal runner effect. Moreover, the amplitude of the radial forces is directly proportional to the flow rate. Furthermore, the spectral analysis shows that the radial force frequency is close to the blade passing frequency and also increases radially outward since peak values were recorded in this region. Minimal radial force amplitudes were recorded when z = 3, across all flow conditions, making this configuration suitable for smooth and reliable operation. The unstable pressure and force pulses that affect the noise and vibration produced in the turbine are instigated by the flow exchange that occurs between the guide vane and the runner. In order to optimize turbines for increased operational dependability, the acquired data would be crucial references for noise and vibration analytical investigations.

In the present research, an artificial neural network was designed and conducted to thermodynamically analyze performance variables of two-shaft radial flow gas turbine model GT185. To do this, firstly the needed tests were conducted at different operating conditions and the essential variables like temperature, pressure, rotational speed, mass flow rate which totaled 17 inputs were recorded. Then, using the relations regarding radial flow turbines and the laboratory results, performance variables including compressor, gas turbine and free turbine power and efficiency and finally the cycle heat efficiency were calculated. After calculation of these variables for all laboratory data, a neural network was designed and tested using Matlab software toolbox in order to facilitate the obtaining of performance variables in different operating conditions. In this network, highest errors absolute values of training, verification and testing data were 0. 32, 0. 86 and 1. 39 respectively. Error value of the produced function of sample laboratory results and manual calculations was less than 0. 1%

In this research, the aerodynamic design of a radial inflow turbine impeller is carried out using a direct design Method. This new method consists of 2 steps; one dimensional design and three dimensional design. In this design, the blade 3D geometry is obtained with new method. Moreover flow properties in various blade points can be investigated. The advantages this method in comparison with previous other method is less time & cost consuming and more accuracy. At the first step of the aerodynamic design, 10 design is done. This program's inputs consists of; stagnation temperature, stagnation pressure, mass flow rate and pressure ratio. The goal of I-d design is to obtain according to optimum experimental data. This procedure based on impeller efficiency convergence. At the second part of this research, by developing a novel design method, the 3D profiles of blade and impellers will be obtained. To validate of one dimensional design results, experimental results and for three dimensional designs, Computational fluid dynamic (CFD) analysis is used. In all this steps, good agreement is observed.

In this work, numerical investigation of a double-swirled gas turbine model combustor (GTMC) was carried out using RANS approach with three different turbulence models of RNG k-e, Realizable k- e and RSM, and two different turbulence-chemistry interaction models of EDC (Eddy Dissipation Concept) and TPDF (Transported Probability Density Function). A detailed reduced mechanism of DRM22 (with 22 species and 104 reactions) was used to represent the chemical reactions. GTMC with a good optical access for laser measurements provided a useful database for swirling CH4/Air diffusion flames at atmospheric pressure. Comprehensive comparisons were done for the predictions and measurements of velocity, mixture fraction, temperature, and chemical species concentrations of H2, O2, OH, H2O, CH4, CO, and CO2 Results showed an acceptable accuracy of predictions. This means that the simplified 2D-axisymmetric simulation has the ability to capture the important features and structure of combustion field in a double highly swirled chamber, like GTMC, with much lower CPU time in comparison with the costly 3D simulations. This study illustrated that using RSM turbulence model presents acceptable results for the flow field, while the other turbulence models were not capable of capturing quantitively acceptable results. In terms of comparison between the turbulence-chemistry interaction models, TPDF led to a good prediction for major species and flame structure near the inlets, while the EDC predicted more accurately downstream of the flow field. Morever, the analysis of flame structure showed that mixing of fuel and oxidizer under double-swirl configuration happens fast and in high levels. In addition, using this type of mixing led to stabilization of main reaction zone in the center of combustion chamber near the injection plane. As a result, under double-swirl injection configuration clean and high quality combustion with reduced size of combustion chamber can be achieved simultaneously.

The present paper describes a numerical investigation of a confined swirling flow in a model combustion chamber. Two turbulence models, the standard k-E model and the Reynolds stress model (RSM) are employed for the flow predictions. Solutions to the two-dimensional axisymmetric incompressible Reynolds-averaged Navier-Stokes equations have been obtained by the Finite- Volume method. Comparisons of the present numerical predictions with the available experimental data reveal superiority of the RSM over the standard k-E model for prediction of swirling flows. For instance, RSM predicts the central toroidal recirculation zone well, but k-E does not.

The performance of turbine section of a gas turbine deteriorates over operation because of working in high temperature conditions and characteristics of the entry gas. On the other hand, due to complexity of the flow field within the turbine, three-dimensional analysis is required. This paper presents a numerical study of roughness effects on turbine flow field and performance. In this paper, effects of blade surface roughness caused by operation conditions on turbine performance were numerically calculated. Numerical calculations were carried out for the fourth stage of an axial turbine which was experimentally tested in the technical university of Hannover, using ANSYS software. Calculated results were verified with the measured data and showed a good agreement. To find out the effects of blade surface roughness on turbine stage performance and flow field, Two equivalent sand-grain roughness heights of 106㎛ (transitionally rough regime) and 400 mm (fully rough regime) in four different mass flow rates were considered. Results showed that summation of efficiency reductions of the rough stator and rough rotor approximately equals to that of the totally rough stage for each roughness height and effect of stator roughness on efficiency reduction is same as the effect of rotor roughness on stage efficiency.