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Publication Title | ANALYSIS OF RADIAL AND MIXED FLOW TURBINE VOLUTES

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DESIGN AND FLOW ANALYSIS OF RADIAL AND MIXED FLOW TURBINE VOLUTES
M Abidat* , M K Hamidou, M Hachemi And M Hamel Laboratoire de Mécanique Appliquée, Faculté de Génie Mécanique Université des Sciences et de la Technologie d’Oran - Algérie e-mail : miloud_abidat04@yahoo.fr
Key Words: Volute, mixed flow turbine, performance, flow angle, efficiency, finite volume method, ANSYS-CFX
ABSTRACT. Radial and mixed flow turbines which are an important component of a turbocharger consist essentially of a volute, a rotor and a diffuser. Vaneless volute turbines, which have reasonable performance and low cost, are the most used in turbochargers for automotive engines. Care has to be done in the design of the volute, whose function is to convert a part of the engine exhaust gas energy into kinetic energy and direct the flow towards the rotor inlet at an appropriate flow angle with reduced losses.
Turbulent compressible flow analysis and performance prediction using the finite volume method implemented in the ANSYS-CFX software, are carried out on two different volute types. Four volute, with different cross section areas used for radial turbines, are studied and the computed results such as the computed averaged volute exit flow angles, the volute overall loss coefficients and the exit radial velocity component distributions are compared with the available experimental data. The second volute studied is the one used for a mixed flow turbine in the turbocharger test rig at Imperial College. In this part of the study, the interest is focused on the influence of the volute inlet flow conditions on its performance (efficiency, exit flow angle, etc).
1 INTRODUCTION
The turbine which is an important component of a turbocharger consists essentially of a casing or volute, a rotor and a diffuser. The casing, whose function is to convert a part of the engine exhaust gas energy into kinetic energy and direct the flow towards the rotor inlet at an appropriate flow angle, can be vaneless or fitted with a nozzle guided vanes. In the second case, the turbine has a good aerodynamic performance at design conditions but a poor efficiency at off design conditions compared with a vaneless stator.
The design for better performances of the spiral housing volute used commonly in radial and mixed flow turbines is of prime importance as it affects the stage performance at both design and off design conditions. Special attention has to be paid to the spiral flow passage surrounding the periphery of the stator. Its major roles are to collect the turbine inlet flow and to deliver it properly all around the periphery of the stator and the rotor blade passages at an appropriate flow direction dictated by optimum turbine efficiency considerations. The volute is fed by a tangential inlet pipe making the gradual transition to the discharge outlet. The inlet shape and length impacts on the turbine efficiency are very important. Chapple et al
European Conference on Computational Fluid Dynamics ECCOMAS CFD 2006 P. Wesseling, E. Oñate, J. Périaux (Eds)
 TU Delft, The Netherlands, 2006

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MicroAD: This research and pdf compilation was sponsored Infinity Turbine Turn your waste heat into energy to save on grid based power or sell back to the grid Organic Rankine Cycle utilizes waste heat to make power. Infinity Turbine Waste Heat to Power Solutions

RADIAL-OUTFLOW-TURBINE: In a radial outflow turbine the organic fluid enters the disk axially in its center and expands radially through a series of stages mounted on the single disk. At the discharge of the last rotor row the flow passes through a radial diffuser and is then conveyed to the recuperator and or condensa- tion section of the system, through the discharge volute. In the early 20th century, Parsons Siemens and Ljungstrom developed the first steam based radial outflow turbines. These early model turbines required a large number of stages. For very high enthalpy drop fluids, such as steam, a single-disk/multi stage configuration was therefore deemed not suitable due to the very large diameter disk necessary to accommodate all the required stages. No further development of the radial outflow turbines oc- curred, as they were phased out for steam applications by axial turbines.

The Geothermal Radial Outflow Turbine: An innovative turbine configuration for geothermal applica- tions was developed by the Italian turbine manufacturer EXERGY. The technology, known as the organic radial outflow turbine was designed, engineered, manufactured and tested in Italy. A 1 MWe geothermal organic Rankine cycle (ORC) equipped with the EXERGY radial outflow turbine has been in operation since early 2013. The radial outflow turbine is a new type of turbine that have the potential to increase the geothermal binary power plants ef- ficiency by increasing the turbine efficiency. The operational results has been positive and demonstrates the viability of the technology and the possibility to develop it for bigger sizes.

Preliminary Design and Off-Design Analysis of a Radial Outflow Turbine for Organic Rankine Cycles: Recently, the advantages of radial outflow turbines have been outstanding in various operating conditions of the organic Rankine cycle. However, there are only a few studies of such turbines, and information on the design procedure is insufficient. The turbine target performance could be achieved by fine-tuning the blade angle of the nozzle exit. In addition, performance evaluation of the turbine against off-design conditions was performed. Ranges of velocity ratio, loading coefficient, and flow coefficient that can expect high efficiency were proposed through the off-design analysis of the turbine.

Study on applicability of radial-outflow turbine type for 3 MW WHR organic Rankine cycle: The article presents the results of study on the reasonability of using radial-outflow turbines in ORC. Peculiarities of radial-outflow turbine design utilizing modern design technologies and application to ORC was considered in the first part of the paper. For this particular cycle design, turbines of radial-outflow type were chosen. Their application enables the increase of mechanical output power by 11 percent compared to original radial-inflow turbines.

LOSS GENERATION IN RADIAL OUTFLOW STEAM TURBINE CASCADES: Small high-speed technology based radial outflow steam turbines are characterised by ultra-low aspect ratios, which can lead to rapidly growing secondary losses. The prelimi- nary evaluation of turbine performance is usually based on axial turbine loss predictions, which can be a source of error. The main objectives of this work are to find out how the losses are generated in radial outflow turbines when the aspect ratio is markedly below unity and how accurately axial turbine loss models can predict the trends. To achieve these objectives, a radial outflow turbine cascade having a blade shape and aspect ratios comparable with a prototype machine is examined. As a result of the study, it is suggested that for the examined radial outflow cascade the axial turbine loss correlations can predict the trends reasonably well. The rapidly increasing secondary losses are connected to the merging of secondary structures and also incidence at off-design.

PRELIMINARY DESIGN OF RADIAL-INFLOW TURBINES FOR ORGANIC RANKINE CYCLE POWER SYSTEMS CONSIDERING PERFORMANCE AND MANUFACTURABILITY ASPECTS: In order to make organic Rankine cycle power systems economically feasible, it is essential to find a reasonable trade-off between the performance and the initial cost of system. In order to show its relevance in a practical application, the method is applied to two radial-inflow turbines cases: a state-of-the-art turbine using air and a turbine using the working fluid Novec 649 for a heat recovery application. The results indicate that there exists a trade-off between turbine performance and manufacturability, and that it is possible to develop turbine solutions with similar values of efficiency with improved manufacturability indicator by up to 14 to 15 percent.

DESIGN AND FLOW ANALYSIS OF RADIAL AND MIXED FLOW TURBINE VOLUTES: Radial and mixed flow turbines which are an important component of a turbocharger consist essentially of a volute, a rotor and a diffuser. Vaneless volute turbines, which have reasonable performance and low cost, are the most used in turbochargers for automotive engines. Care has to be done in the design of the volute, whose function is to convert a part of the engine exhaust gas energy into kinetic energy and direct the flow towards the rotor inlet at an appropriate flow angle with reduced losses.

An Exploration of Radial Flow on a Rotating Blade in Retreating Blade Stall: The nature of radial flow during retreating blade stall on a two-bladed teetering rotor with cyclic pitch variation is investigated using laser sheet visualization and particle image velocimetry in a low-speed wind tunnel. The velocity field above the retreating blade at 270◦ azimuth shows the expected development of a radially directed jet layer close to the blade surface in the otherwise separated flow region. This jet is observed to break up into discrete structures, limiting the spanwise growth of the radial velocity in the jet layer. The discrete structures are shown to derive their vorticity from the “radial jet” layer near the surface, rather than from the freestream at the edge of the separated region. The separation line determined using velocity data shows the expected spanwise variation. The results of this study are also correlated in a limited range of extrapolation to the phenomena encountered on a full-scale horizontal axis wind turbine in yaw.

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