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The uncooled, 2.27 kg/sec mass flow radial turbine designed to operate at 1477 K in the gas generator of an advanced, variable-capacity 683 kW turboshaft engine was configured with a cooled, movable sidewall nozzle capable of changing the stage flow capacity from 50 to 100 percent of maximum. Overall performance test data were obtained in a turbine test rig that duplicated engine Reynolds numbers; attention is given to the changing of flow capacity by moving the hub or shroud sidewall, vane sidewall leakage, vaneless space sidewall geometry, and nozzle-cooling injection. Data are presented in the form of turbine flow, efficiency, work parameter, and performance mappings.

An off-design performance loss model for a radial turbine with pivoting, variable-area stators is developed through a combination of analytical modeling and experimental data analysis. A viscous loss model is used for the variation in stator loss with setting angle, and stator vane end-clearance leakage effects are predicted by a clearance flow model. The variation of rotor loss coefficient with stator setting angle is obtained by means of an analytical matching of experimental data for a rotor that was tested with six stators, having throat areas from 20 to 144% of the design area. An incidence loss model is selected to obtain best agreement with experimental data. The stator vane end-clearance leakage model predicts increasing mass flow and decreasing efficiency as a result of end-clearances, with changes becoming significantly larger with decreasing stator area.

This paper presents a numerical analysis and experimental measurements of flows in the vaneless volute of a radial–inflow turbine. Cases of single and twin entry to the volute were studied, and in particular the case of unequal flows, or partial admission, to the two entries. The distance between the rotor tip and the limit of the internal wall separating the two flows was varied in order to study the effects of interaction of the two streams. The computational model is based on a quasi–three–dimensional solution of the Euler equations, in which the radial and tangential components of velocity are fully solved, but the axial component is only treated to simulate the mixing of the two streams. The results of the model were compared with published results for a single entry, and extensive new results for a single or twin entry, casing. Even in the single and equal flow twin–entry cases, significant variations in flow properties around the exit circumference of the volutes were observed, most particularly in the region of re–entry near the tongue. For unequal flows the interaction of the two streams was strong and increased with increasing separating wall diameter, and with increasing inequality of flow rates. In extreme cases the flow reverses.

Since the Kongsberg KG5 gas turbine was introduced into service in 1977 these engines have accumulated more than 100 000 hours of field operation. Apart from an exducer blade vibration problem which was revealed and fixed prior to field introduction, no major operational problems have been encountered. During test and commissioning of two larger orders, three separate incidents of turbine blade failure occurred, one in March 1982 and two in February 1983. The first incident triggered a number of investigative actions and the resulting conclusion was confirmed by the last two incidents. The present paper describes the analytical and test methods employed in order to investigate this problem. The blade natural frequencies were determined analytically through a NASTRAN analysis and experimentally with a TV-Speckle Interferometer technique. It is shown how the influence of an interference fit or dampening joint between the two rotor wheels was actually hiding the possible resonance condition during the initial qualification tests, and how the transient movements of this joint would allow resonance to occur under certain operational conditions. The possible corrective modifications are discussed and the selected solution is shown. The test set up and the results from the verifying strain gauge test is presented.

The results of an investigation of the particle dynamics and the blade erosion at the impact locations in radial turbine guide vanes are presented. The attention is focused in particular on the effect of inlet flow angle on the erosion of the blades, since the flow entering the guide vanes usually has an incidence angle due to the upstream scroll geometry. The total erosion per blade is calculated as a function of inlet flow angle for three different particle diameters which are 5, 15 and 60 microns respectively. According to the results of this investigation, for each particle size there is an inlet flow angle for minimum erosion of the guide vanes. This fact has to be accounted for in the design of the radial turbines operating in particulate flow environments.Copyright © 1989 by ASME

With reference to two batches of rotors, the discussion of component development results shows the problem areas in the fabrication, quality inspection and testing of ceramic radial rotors. Following the evaluation of the present results, future development work must concentrate on the improvement of - material quality (microstructure, strength) - component fabrication, i.e. injection molding - binder removal - sintering - mechanical finishing - joining techniques.

Incidence losses occur when the gas flow angle does not coincide with the blade angle. Several incidence models which are available to the designer are reviewed and a new method of calculating the incidence losses in the stator and rotor of a mixed flow radial turbine is presented. The results from this model have been compared in the case of a mixed flow radial turbine rotor with the results from the other models and with the experimental results for the stator. All the models assume a change in the tangential component of kinetic energy at stator or rotor inlet. It is concluded that none of these models is satisfactory because they do not take into account the flow pattern in the rotor or stator passages.Copyright © 1982 by ASME

This paper describes fabrication of silicon nitride radial turbine wheels 90 mm in diameter. The wheels were hot spin tested without failure at turbine tip speeds up to 600 m/s. The reliability of shrink fit of metal shaft and ceramic wheel was demonstrated in a turbocharger test. Results of the hot spin test are discussed in relation to the nature of defects and compared with the analytic prediction using Weibull statistics and finite element analysis.

While the radial in-flow turbine has consistently demonstrated its capability as a high-performance component for small gas turbine engines, its use has been relegated to lower turbine-inlet-temperature cycles due to insurmountable problems with respect to the manufacturing of radial turbine rotors with internal cooling passages. These cycle temperature limitations are not consistent with modern trends toward higher-performance, fuel-conservative engines. This paper presents the results of several Army-sponsored programs, the first of which addresses the performance potential for the high-temperature radial turbine. The subsequent discussion presents the results of two successful programs dedicated to developing fabrication techniques for internally cooled radial turbines, including mechanical integrity testing. Finally, future near-term capabilities are projected.Copyright © 1981 by ASME

A quasi-steady-state analysis is made of the performance of a gas-turbine working with intermittent, constant volume combustion. Variables considered include inlet temperature, compressor pressure ratio, scavenge ratio, combustion time, heat exchanger thermal ratio. Characteristics are computed over a full loading range. Computations are based on turbines having the following behavior: (a) constant turbine efficiency, (b) characteristics of a multistage axial turbine, and (c) characteristics of a single-stage radial turbine. The analysis indicates that the constant volume gas turbine has advantages in thermal efficiency, specific power and part load performance over constant pressure gas turbines operating at the same compressor pressure ratio and turbine inlet temperature. However, the addition of a heat exchanger shows less advantage when applied to a constant volume than to a constant pressure engine.Copyright © 1974 by ASME

An acceptable and feasible ceramic turbine wheel design has been achieved, and the relevant temperature, stress, and success probability analyses are discussed. The design is described, the materials selection presented, and the engine cycle conditions analysis parameters shown. Measured MOR four-point strengths are indicated for room and elevated temperatures, and engine conditions are analyzed for various cycle states, materials, power states, turbine inlet temperatures, and speeds. An advanced gas turbine ceramic turbine rotor thermal and stress model is developed, and cumulative probability of survival is shown for first and third-year properties of SiC and Si3N4 rotors under different operating conditions, computed for both blade and hub regions. Temperature and stress distributions for steady-state and worst-case shutdown transients are depicted.

A method for predicting the deviation angle at exit from the nozzles of an inward flow radial turbine using a streamline curvature method is given. Measurements of flow angles and stagnation and static pressures across the nozzle exit span of a small turbine have been made. The accuracy of the analysis is shown by comparison with experimental results. Finally, the developed theory has been used to show the possible effect on the deviation angle at exit from the nozzles of reducing the number of stator blades.Copyright © 1980 by ASME

The objective of this program was to provide and demonstrate the technology required to economically manufacture a cooled, high-temperature, radial turbine with sufficient integrity and aerodynamic performance to meet future Army requirements for a reliable, low-cost, high performance, small gas turbine engine. The work to accomplish this objective was subdivided into three phases. (Author)

The design of a small inward flow turbine with a 3.6 expansion ratio has been undertaken by MICROTURBO, in cooperation with ONERA for calculations and test results analysis. Initially, the purpose and constraints of this study are underlined. Preliminary calculations have led to the design of the blade shape of the Nozzle Guide Vane and of the rotor. Following this, the results of the quasi-3D-flow computations, performed for the stator and the rotor, are given. Both the cold bench tests on this turbine and the corresponding hot tests on the turboshaft engine enable performances to be checked. The value of the calculations is confirmed when we look at the high total and static adiabatic efficiencies obtained. These good results are encouraging for the future use of this kind of turbomachine.

The radial, or centripetal, turbine is used for very small flows, where it is cheaper and simpler to make than an axial flow turbine. It is used in the smallest gas turbine engines, as in some automotive or fire pump or other portable applications, and is used extensively in the smaller turbochargers. It is also suitable for turbo-expansion applications (section 2.9). Its size ranges up to about 0.15 m diameter, and its rotational speed is likely to be between 60 000 and 100 000 rev/min.

A procedure for computing the rotor temperature and stress distributions in a cooled radial turbine is considered. Existing codes for modeling the external mainstream flow and the internal cooling flow are used to compute boundary conditions for the heat transfer and stress analyses. An inviscid, quasi three-dimensional code computes the external free stream velocity. The external velocity is then used in a boundary layer analysis to compute the external heat transfer coefficients. Coolant temperatures are computed by a viscous one-dimensional internal flow code for the momentum and energy equation. These boundary conditions are input to a three-dimensional heat conduction code for calculation of rotor temperatures. The rotor stress distribution may be determined for the given thermal, pressure and centrifugal loading. The procedure is applied to a cooled radial turbine which will be tested at the NASA Lewis Research Center. Representative results from this case are included.

The report describes the design, fabrication and test of a radial turbine designed to produce 219.6 Btu/lb stage work at 87.5% efficiency, with a 5:1 stage pressure ratio. Turbine inlet gas conditions at design point were 257. 5 psia and 2300F. The resulting turbine configuration consisted of an air- cooled, 12-bladed rotor designed for 67,000 rpm, and a 20-vaned air-cooled nozzle section of a reflex-type (supersonic) design. Both parts were designed as IN100 (PWA 658) investment castings. As part of the preliminary design effort, a fabrication study was conducted to evaluate feasible methods of casting the turbine nozzle and rotor. Results showed that the nozzle section could be cast as an integral assembly, but fabrication of the rotor as an integral casting was much more difficult. Bicasting was evaluated as an alternate method of fabricating the rotor, and results showed substantial advantages for the bicasting technique. However, neither method could produce designed rotor properties, and testing was conducted with structurally limited rotors. A test rig was designed and fabricated by the contractor. The test rig consisted of a supercharged gas generator, which had the capability of controlling the turbine load by varying the compressor flow rate. Burner testing preceded turbine testing.

This study was conducted to establish the performance parameters of a radial in-flow, dual discharge turbine and to determine the effect of axial clearance on these parameters. The results of the tests can be utilized for design improvements and for predicting off-design operating conditions. The air tests of the turbine were made at several total-to-static pressure ratios. The study presents data obtained from measured rotor discharge flow conditions as well as overall turbine conditions. The test turbine is installed at the Propulsion Laboratory of the Naval Postgraduate School, Monterey, California. http://archive.org/details/theeffectofaxial1094543296 US Navy (USN) author Approved for public release; distribution is unlimited.

The high efficiencies of small radial turbines have led to their application in space power systems and numerous APU and shaft power engines. Experimental and analytical work associated with these systems has included examination of blade shroud clearance, blade loading, and exit diffuser design. Results indicate high efficiency over a wide range of specific speed and also insensitivity to clearance and blade loading in the radial part of the rotor. The exit diffuser investigation indicated that a conventional conical outer wall may not provide the velocity variation consistent with minimum overall diffuser loss. A list of recently published NASA radial turbine reports is included.

The design of a high-temperature, high-work radial turbine for advanced small gas turbine engines is described. This turbine is designed to produce nearly 220 Btu/lb gas flow at 87.5% efficiency, with a 5:1 stage pressure ratio. Turbine inlet gas conditions are 17.5 atm and 2300°F. The resulting turbine configuration includes an air-cooled, 12-bladed rotor designed for 67,000 rpm, and a 20-vaned, air-cooled nozzle section of a reflex (supersonic) design. Both parts are IN 100 (PWA 658) investment castings. The discussion includes results of aerodynamic, structural, and thermal analyses. Also discussed is a fabrication study, which indicated that a casting development effort would be required to produce adequate material properties. This effort is currently underway, and consists of both an integral centrifugal casting approach and a bicasting technique. The test rig to be used for the turbine tests is described.

Under on-engine operating conditions, a turbocharger turbine is subject to a pulsating flow and, consequently, experiences deviations from the performance measured under continuous flow. Furthermore, due to the high exhaust gas temperatures, heat transfer further deteriorates the turbine performance. The complex interaction of the aerothermodynamic mechanisms occurring inside the hot-side, and consequently the turbine behavior, is largely affected by the shape of the pulse, which can be parameterized through three parameters: pulse amplitude, frequency, and temporal gradient. This paper investigates the hot-side system response to the pulse amplitude via a Detached Eddy Simulation (DES) approach of a radial turbocharger turbine system including exhaust manifold. Firstly, the computational model is validated against experimental data obtained under gas stand continuous flow conditions. Then, two different mass flow pulses, characterized by a pulse amplitude difference of ≈ 5%, are compared. An exergy-based post-processing approach shows the beneficial effects of increasing pulse amplitude. An improvement of the turbine power by 1.3%, despite the increment of the heat transfer and total internal irreversibilities by 5.8% and 3.4%, respectively, is reported. As a result of the higher maximum speed, internal losses by viscous friction are responsible for the growth of the total internal irreversibilities as pulse amplitude increases.

Despite the increasing number of Organic Rankine Cycle (ORC) installations at megawatt scale, the waste heat rejected by industrial processes can vary substantially from a few kWh to many megawatt hours. Hence, ORC units with a power output in the range of tens of kilowatts should be developed to tackle the heat recovery and business opportunities that can arise from this market segment. In the current research activity, a dynamic model of a small scale ORC system was developed using a commercial software platform. The unit is equipped with two plate heat exchangers, a centrifugal pump and a radial turbine designed and optimized using an in-house code and a commercial 1D modelling tool. The off-design behaviour of the ORC system has been characterized by varying the inlet conditions of heat source and sink, and the revolution speed of the turbomachines. Moreover, the response to transient thermal inputs at different time scales has also been investigated. Finally, four control strategies have been compared from the performance and energy efficiency perspectives. The results show that the turbine based regulation strategies achieve better control performance while pump based controls are able to regulate the system by maintaining the net power output closer to the design point.

The design optimization of turbomachinery components has witnessed an increased attention in last decade, and is currently used in many companies in the daily design cycle. The adjoint method proves to have the highest potential in this field, however, has still two major shortcomings before its full potential can be used: 1) the shape is mainly parameterized by its grid and the connection to the CAD model is lost, and 2) the optimization process includes only aerodynamic performance and neglects stress and vibration requirements. Within this paper a methodology is developed to include stress calculations into a gradient-based framework, which requires the differentiation of a stress analysis tool. To allow combining the sensitivities from the structural model with those from the aero performance, the CAD model is used for parameterizing the shape, effectively defining a parametrization that controls both the fluid and solid domain that remain linked to each other without creating voids between both models. The method is tested on a radial turbine test case in which the meridional layout is optimized to reduce the maximum von Mises stresses in the material. The results demonstrate a significant reduction in stress concentrations with a limited computational cost.

This paper is focussed on the development of an axial inflow turbocharger turbine as a viable alternative to a baseline radial turbine for certain applications. Additionally a variable geometry turbine (VGT) technology is incorporated into the axial-inflow turbine to additionally benefit both efficiency and performance. The developed turbine was compared to the baseline in terms of engine performance, fuel consumption and emissions. The design and optimisation of the inlet casing, stator and rotor blades for axial inflow turbine were developed through CFD simulation. Then a VGT system was further developed, equipped with pivoting stator blades. Necessary data at various flow conditions were collected for engine modelling to test the engine performance achieved by the integration of the axial turbine, which achieved a maximum 86.2% isentropic efficiency at 102,000 rpm. The paper further focussed on the design and optimization of a volute for axial inflow turbine. Various initial designs were tested using CFD simulations and the chosen configuration was optimised further to improve overall stage efficiency, which reached 81.2%. Engine model simulations demonstrated that engine power and torque are significantly increased through the application of the proposed variable geometry axial turbocharger turbine.

Developing small scale turbines pauses challenges in terms of increased stresses due to high rotational speed leading to increase in component thicknesses and turbine overall weight. Therefore this study assesses both; the structural and aerodynamic performance of a Small Scale Radial Turbine SSRT by integrating finite-element methods FEM and Computational Fluid Dynamic CFD. Using Vista preliminary design model in ANSYS and detailed 3D CFD optimization, SSRT with 1–5 kW power for solar powered Brayton cycle was developed with high efficiency of 89.2%. Then both; the turbine’s hub and blades were structurally analysed under various loading conditions to investigate the effect of various rotational speeds and blade shapes on the stress distribution and deformation of the blades. The results of the current study showed that a maximum increment of 65% stress and 57% deformation was noticed when reaching the maximum studied rotational speed at inlet air temperature of 450 K.

This paper presents a control oriented model for predicting turbine major variables in a turbocharged spark ignition engine. The turbine is simulated as a two-nozzle chamber where the pressure ratio over the two nozzles is not the same. A convex nonlinear estimation algorithm is formulated to determine the relation between these pressure ratios. The new model is experimentally validated with transient and steady state data collected from a 1.7 liter gasoline engine. The results show the new model can predict the turbine mass flow with an average error of 1.4%. In addition, the application of the turbine model is illustrated for the design of a nonlinear observer to estimate the turbocharger non-measured variables. The designed observer is tested against experimental data and the results confirm the observer capability to estimate the turbine rotor speed, flow over the compressor and temperature downstream the compressor.

This paper presents investigations carried out at Holset into the dynamics of mistuned\ud radial turbine wheels, including a literature review, a lumped parameter model,\ud identification of the most responsive blade, distribution of the peak maximum order\ud response and a method of mistiming identification.

The aim of this work is to supply some further data on the effect of the suspended solid on reaction selectivity, relating it to the changes in the power input and to the hydrodynamics of the slurry; two different stirrers, a radial turbine and a mixed flow impeller will be considered.