G226 ラジアルタービンのスラストに関する研究(OS7 高温・高効率発電)

: Small radial inflow turbines have various applications in industry and are successfully being used as a major component of gas turbines and turbochargers. The performance of the turbine is of great importance for the success of these systems. Although the design of radial inflow turbines has improved in the last few years, the detailed aerodynamic study of these components still needs considerable attention. Better understanding of the flow processes involved in these machines will provide a good basis for the design of improved components and for this purpose a joint research programme has been undertaken by Cranfield, the US Army Research Office and Turbomach (San Diego). The main objective of the study was to investigate the flow processes involved in the radial inflow turbine using experimental methods. The work presented in this report describes the various steps undertaken to perform these studies together with results. The project involved two phases, the first measurements downstream of the rotor and the second measurements between the nozzle guide vanes and rotor inlet. The scope of the study was limited to two man years during which considerable success was achieved in obtaining the desired measurement but more time to further reduce this data and to compare with computational results, which was outside the scope of the present study, would have been advantageous. The studies using laser anemometry undertaken downstream of the turbine rotor indicated a swirling flow with a region of counter-rotating flow in the centre. A cobra probe was used to compare with the laser anemometry results. Both measuring techniques show similar trends of flow velocity and flow angle at various running conditions.... Radial Turbines, Laser Anemometry.

The blades of turbocharger impellers are exposed to unsteady aerodynamic forces, which cause blade vibrations and may lead to failures. An indispensable requirement for a safe design of radial inflow turbines is a detailed knowledge of the exciting forces. Up to now, only few investigations relating to unsteady aerodynamic forces in radial turbines were presented. To give a detailed insight into the complex phenomena, a comprehensive research project was initiated at the Institut für Thermische Strömungsmaschinen, at the University of Karlsruhe. A turbocharger test rig was installed in the high pressure, high temperature laboratory of the institute. The present paper gives a description of the test rig design and the measuring techniques. The flow field in a vaneless radial inflow turbine was analyzed using laser Doppler anemometry. First results of unsteady flow field investigations in the turbine scroll and unsteady phase resolved measurements of the flow field in the turbine rotor will be discussed. Moreover, results from finite element calculations analyzing frequencies and mode shapes are presented. As vibrations in turbines of turbochargers are assumed to be predominantly excited by unsteady aerodynamic forces, a method to predict the actual transient flow in a radial turbine utilizing the commercial Navier Stokes solver TASCflow3d was developed. Results of the unsteady calculations are presented and comparisons with the measured unsteady flow field are made. As a major result, the excitation effect of the tongue region in a vaneless radial inflow turbine can be demonstrated.

Turbochargers are finding increasing application to automotive diesel engines as cost effective means for improving their power output and efficiency, and reducing exhaust emissions; these requirements have led to the need for highly loaded turbocharger turbines. A mixed-flow turbine is capable of achieving its peak isen-tropic efficiency at reduced velocity ratios compared to a typical radial inflow turbine; it is therefore possible to improve the turbocharger/engine matching. These turbines differ from the commonly used radial turbines in that the flow approaches the rotor in the non-radial direction; in the extreme a mixed-flow turbine would become an axial machine. The steady and unsteady performances of a mixed-flow turbocharger turbine with a constant blade inlet angle have been investigated. The steady flow results indicated that the mixed-flow turbine obtains a peak efficiency (total-to-static) of 75 per cent at a velocity ratio of 0.61, compared with that of a typical radial-inflow turbine which peaks at a velocity ratio of 0.7. The performance and flow characteristics were found to deviate significantly from the equivalent steady state values commonly used in turbocharger turbine design.

<title>Abstract</title> Radial turbines are widely employed in turbochargers, where they can be paired with compressors to improve energy efficiency in power generation and recovery applications. Optimizing turbine rotor design is critical for maximizing efficiency, yet conventional approaches often rely heavily on empirical methods with limited flexibility. This study develops an integrated design methodology that integrates simplified one-dimensional (1D) formulations with advanced computational fluid dynamics (CFD) analyses to streamline the radial turbine rotor design process. The tool first applies 1D equations to identify feasible initial candidates for key rotor design parameters. It then constructs a design domain by specifying boundary values for every parameter. Within this space, multiple design scenarios are tested using CFD simulations, allowing for detailed performance evaluation and identification of optimal geometries. The tool was applied to the radial turbine in the Borg-Warner K03/05 turbocharger as a case study. Using the methodology, a CAD model of the turbine rotor was generated that met the specified design requirements. The optimized rotor demonstrated an increase in operational efficiency 2% compared to the initial design, the findings substantiate the effectiveness of the integrated framework. The proposed design tool successfully combines 1D modeling with CFD to provide a systematic and flexible framework for radial turbine rotor design. By efficiently exploring a wide design space, it enables the identification of high-performance rotor geometries that improve efficiency beyond conventional designs. This method can be extended to broader applications in energy recovery and turbocharging systems.

Preliminary design, optimization and CFD analysis of an organic rankine cycle radial turbine rotor

In the present paper, an unsteady approach to determine the performance of a small radial inflow turbine working under cold pulsating flow is presented. It has been concluded that a reasonably good characterization of turbine behavior working with pulsating flow can be obtained using, in a quasi-steady way, models of the turbine isentropic efficiency and turbocharger mechanical efficiency. Both models have been fitted using data obtained from a steady flow characterization procedure. Turbocharger-measured parameters from the cold pulsating flow campaign have been compared with the ones obtained from one-dimensional gas dynamics computational modeling. The modeling approach is based on quasi-steady isentropic and mechanical efficiency models. Reasonably good accuracy in compressor and turbine variables prediction has been obtained for most of the operative conditions. Influence of amplitude and frequency of the pulsating flow over the instantaneous and average turbine efficiency has been studied to put some light on the analysis of the involved physical phenomena. The main conclusion is that the biggest effect of unsteady flow on turbine efficiency is through the influence on blade jet to speed ratio. It has been also concluded that, for the same average blade jet to speed ratio, pulses’ amplitude does not influence turbine efficiency when it is closed, but does at other variable geometry turbine (VGT) positions. The effect of pulses’ frequency is less evident and only influences VGT performance at the highest VGT openings.

Cycles using supercritical carbon dioxide have been recognized as potential future power technology. However, the turbines in these systems tend to experience very high rotational speeds and entail small physical sizes, which can affect on the overall feasibility. One turbine type having potential to overcome some of the described challenges is the radial outflow turbine. However, its use in supercritical carbon dioxide power systems has not yet been extensively studied since typically axial or radial inflow turbines are considered instead. In this paper, the design of radial-outflow turbines with supercritical carbon dioxide is carried out and the results are compared to the respective radial inflow turbine designs. The analysis was carried out with turbine inlet temperature of 600 °C, inlet pressure of 200 bar and outlet pressure of 78 bar. Designs with four mass flow rates were investigated to study the effect of the power scale on the turbine design and losses. The geometry, efficiency, rotor stress and axial force were defined and analyzed for each design case. The results show that both the investigated turbine types can reach high isentropic efficiencies ranging from about 85% to over 90%. The radial outflow turbines can reach high efficiencies at wider specific speed range whereas the efficiency of radial inflow turbine is reduced more steeply, as the design speed is changed from its optimal value. Radial outflow turbines also reach high efficiencies with lower design speeds and that can be considered advantageous, since it helps to reduce the challenges related to turbomachinery rotordynamic and mechanical design. As a conclusion of the study, it is suggested that the use of radial outflow turbines can increase the feasibility of supercritical carbon dioxide power systems at the examined power scales.

In the second part of this two part paper, the condensation process and the movement of the liquid phase near the impeller blades of a radial turbine are studied. The investigation methodology presented in part 1 is applied to a radial turbine type series used for waste heat recovery. First, the subcooling necessary for the beginning of the condensation process is examined and a relationship between the location of maximum subcooling and the onset of droplet deposition at the surfaces of the turbine impeller is determined. Thereafter, the movement of liquid films on the impeller blades is analysed and characterized. Correlations determining the movement of droplets originating from liquid film atomization on the edge of the impeller blade along the casing are derived. Finally, conclusions are drawn depicting the most important findings of condensing flows in radial turbines.

Results of an investigation of the development of a class of highly efficient steam turbines in the 500 to 5000 horsepower range are presented; these new machines are expected to have efficiences between 70 and 85%. The turbines are based on the concept of one or more high-speed radial inflow turbine modules driving a low-speed bull gear. Each module operates then at optimal specific speed, which yields high efficiency compared to the partial admission Curtiss stages currently used. The project has two phases. Phase 1 includes investigation and interpretation of the market for small steam turbines and definition of the radial inflow turbine (RIT) configurations best suited to penetrate a significant portion of this market. Phase 1 concludes with a recommended configuration. (MCW)

This paper presents a CFD-based numerical analysis on the potential benefits of non-radial blading turbine for low speed-low pressure applications. Electric turbocompounding is a waste heat recovery technology consisting of a turbine coupled to a generator that transforms the energy left over in the engine exhaust gases, which is typically found at low pressure, into electricity. Turbines designed to operate at low specific speed are ideal for these applications since the peak efficiency occurs at lower pressure ratios than conventional high speed turbines. The baseline design consisted of a vaneless radial fibre turbine, operating at 1.2 pressure ratio and 28,000rpm. Experimental low temperature tests were carried out with the baseline radial blading turbine at nominal, lower and higher pressure ratio operating conditions to validate numerical simulations. The baseline turbine incidence angle effect was studied and positive inlet blade angle impact was assessed in the current paper. Four different turbine rotor designs of 20, 30, 40 and 50° of positive inlet blade angle are presented, with the aim to reduce the losses associated to positive incidence, specially at midspan. The volute domain was included in all CFD calculations to take into account the volute-rotor interactions. The results obtained from numerical simulations of the modified designs were compared with those from the baseline turbine rotor at design and off-design conditions. Total-to-static efficiency improved in all the non-radial blading designs at all operating points considered, by maximum of 1.5% at design conditions and 5% at off-design conditions, particularly at low pressure ratio. As non-radial fibre blading may be susceptible to high centrifugal and thermal stresses, a structural analysis was performed to assess the feasibility of each design. Most of non-radial blading designs showed acceptable levels of stress and deformation.

The paper describes a test facility for small-scale gas turbines, which basically has been designed and assembled at the Institute of Combustion Engines of the Technical University Berlin. The facility exposes ceramic rotor components to the most significant loads that occur during real gas turbine operation in a clearly predefined manner (high circumferential velocities and highest turbine inlet temperatures). The test facility allows the investigation of bladed radial inflow turbine rotors, as well as — in a preceding step — geometrically simplified ceramic or coated metallic rotors. A newly designed, ceramically lined, variable geometry combustion chamber allows turbine inlet temperatures up to 1450°C (2640 F). A fast thermal shock unit (switching time of about 1s), which is integrated into the test facility between the combustion chamber and the turbine scroll, can be used to create, for example, severe transient temperature gradients within the rotor components to simulate gas turbine trip conditions. In order to generate steady state temperature gradients, especially during disk testing, the rotor components can be subjected to an impingement cooling of the rotor back face (uncoated in case of TBC-testing). The test facility is additionally equipped with a non-contact transient temperature measurement system (turbine radiation pyrometry) to determine the test rotor surface temperature distribution during operation. Apart from the possibilities of basic rotor material investigations, the test facility can also be used to automatically generate compressor and turbine performance characteristics maps. The latter might be used to assess the aerodynamic performance of bladed ceramic radial inflow or mixed flow turbine rotors with respect to manufacturing tolerances due to near-net-shape forming processes (e.g., gelcasting or injection molding).

In case of small torque air turbine has often been used for the purpose to obtain high speed, for example to drive Gyro, Ultracentrifuge, and Internal-Grinder etc. In this case, usually radial flow impulse type has been adopted for its simple construction. It appears that there are few reports proposed up to this time concerning the turbine of such type with which we can conclude turbine efficiency, and so concerning Parallel nozzles used for it. An investigation was made to present a complete design data applied qualitatively to this type turbine design. The contents of this paper are as follows : (1) The characteristics of the radial flow type air impulse turbine and the best profile of buckets have been presented and checked by experiments. (2) Experiments of the radial flow type air reaction turbine have been given. (3) The author points out that bucket velocity coefficient of the turbines of this type will be about 0·6, and the comparison of the two has been discussed. (4) Results of reaction tests of parallel nozzles have been given, and he presents analytically simple formulae to conclude velocity and discharge coefficient of parallel. nozzles with arbitrary dimensions.

The state of the boundary layers on the blade surfaces of the rotor of a radial inflow turbine has been investigated using surface-mounted hot-film anemometers. The boundary layers are shown to be laminar or intermittently turbulent at the design flow condition. This is despite the fact that the Reynolds number is relatively high and conventional two-dimensional numerical techniques predict transition at about 20% surface length. The boundary layer does not become fully turbulent because there is strong secondary flow and large acceleration of the flow close to the surface. Surface pressure distributions and an in viscid prediction method are used to assist in the explanation for the state of the boundary layers.

Large-eddy simulation (LES) of compressible low-Reynolds-number (Re) flows in small radial turbines with the rotor diameter of 46mm and 8mm is performed. Conditions of pressure ratio of 1.5 and isentropic velocity ratio of 0.6 are assumed, and the tip clearance of 2.7% the blade height is taken into account. In addition to the computations, Reynolds-averaged Navier-Stokes simulation (RANS) based on the Baldwin-Lomax turbulence model and aerodynamic tests are also conducted. Based on the results, the differences in the prediction of loss between LES and RANS, Reynolds number effects on the intermal flows and a method of efficiency improvement are discussed.

The turbine rotor system (TRS) plays an important role in the high-speed power system. Its vibrations and noise can greatly affect the performance and service life of power system. To study the vibrations of TRS, a finite element (FE) model of TRS is established. The natural frequencies and critical speeds of rotor system are analyzed. The influences of bearing stiffness and support positions of different support ranges on the critical speeds are analyzed. Note that the critical speeds of TRS increase with the increment of the stiffness of bearing. The support positions of bearing #1 have the greatest influence on the critical speeds of TRS. The maximum difference of critical speeds is 916.1 rad/s. The support positions of bearing #4 have the least impact on the critical speeds of TRS. The maximum difference of critical speeds is 8.7 rad/s. The study can provide a reference for the structural design of the turbine rotor system.KeywordsTurbine rotor system (TRS)Critical speedStiffnessSupport positions