Mixed Flow Turbine Research Articles

402 波力タービンに関する研究(流体工学 : 流体機械)

402 波力タービンに関する研究(流体工学 : 流体機械)

Mixed Flow Turbines: Inlet and Exit Flow Under Steady and Pulsating Conditions

The performance and detailed flow characteristics of a high pressure ratio mixed flow turbine has been investigated under steady and pulsating flow conditions. The rotor has been designed to have a nominal constant incidence (based on free vortex flow in the volute) and it is for use in an automotive high speed diesel turbocharger. The results indicated a departure from the quasi-steady analysis commonly used in turbocharger turbine design. The pulsations from the engine have been followed through the inlet pipe and around the volute; the pulse has been shown to propagate close to the speed of sound and not according to the bulk flow velocity as stated by some researchers. The flow entering and exiting the blades has been quantified by a laser Doppler velocimetry system. The measurements were performed at a plane 3.0 mm ahead of the rotor leading edge and 9.5 mm behind the rotor trailing edge. The turbine test conditions corresponded to the peak efficiency point at 29,400 and 41,300 rpm. The results were resolved in a blade-to-blade sense to examine in greater detail the nature of the flow at turbocharger representative conditions. A correlation between the combined effects of incidence and exit flow angle with the isentropic efficiency has been shown. The unsteady flow characteristics have been investigated at two flow pulse frequencies, corresponding to internal combustion engine speeds of 1600 and 2400 rpm. Four measurement planes have been investigated: one in the pipe feeding the volute, two in the volute (40 deg and 130 deg downstream of the tongue) and one at the exit of the turbine. The pulse propagation at these planes has been investigated; the effect of the different planes on the evaluation of the unsteady isentropic efficiency is shown to be significant. Overall, the unsteady performance efficiency results indicated a significant departure from the corresponding steady performance, in accordance with the inlet and exit flow measurements.

Prediction of the steady and non-steady flow performance of a highly loaded mixed flow turbine

This paper describes a method for predicting the performance under both turbine inlet steady state and non-steady state flow conditions of a mixed flow turbine used for turbocharged internal combustion engines. The mixed flow turbine steady state performances computed with the steady state performance prediction method are in good agreement with the experimental results obtained in the Imperial College turbocompressor cold air test rig. The unsteady state performance is computed using a one-dimensional model based on the solution of the unsteady one-dimensional flow equations. These equations are solved in the volute by a finite difference method using a four-step explicit Runge—Kutta scheme. The instantaneous volute exit condition is provided by the steady state rotor performance prediction model with the assumption of a quasi-steady state flow in the rotor. The computed instantaneous performances are in reasonable agreement with published experimental data for the same mixed flow turbine. The unsteady flow model is also used to study the effects of the frequency and the amplitude of the pulse on the performances of the mixed flow turbine.

The exploitation of three-dimensional flow in turbomachinery design

Many of the phenomena involved in turbomachinery flow can be understood and predicted on a two-dimensional (2D) or quasi-three-dimensional (Q3D) basis, but some aspects of the flow must be considered as fully three-dimensional (3D) and cannot be understood or predicted by the Q3D approach. Probably the best known of these fully 3D effects is secondary flow, which can only be predicted by a fully 3D calculation which includes the vorticity at inlet to the blade row. It has long been recognized that blade sweep and lean also produce fully 3D effects and approximate methods of calculating these have been developed. However, the advent of fully 3D flow field calculation methods has made predictions of these complex effects much more readily available and accurate so that they are now being exploited in design. This paper will attempt to describe and discuss fully 3D flow effects with particular reference to their use to improve turbomachine performance. Although the discussion is restricted to axial flow machines, many of the phenomena discussed are equally applicable to mixed and radial flow turbines and compressors.

Exit traverse study of mixed-flow turbines with inlet incidence variation

This paper reports a traverse survey of the flow conditions at the exhaust pipe of two mixed-flow turbines. The experimental method is described and the results discussed. It shows that for both turbines, a shroud-hub flow migration might be generated within the blades at higher pressure ratios, which relieves the high blade loading at the shroud, and a flow separation from the suction side of the hub might occur at the lower pressure ratios. The turbine with ‘constant incidence angle’ rotor design suffered from greater swirl loss and a possible internal flow separation than the one with a constant blade inlet angle.

Computer-Aided Analysis of Hydraulic Reaction Turbines

A microcomputer-based educational software package designed to help mechanical engineering students to understand hydraulic reaction turbines is described. The software is interactive, menu-driven, and easy-to-use, is written in the Pascal computer language, and runs on IBM PC, or compatible, computers. The program can handle radial, mixed, or axial flow turbine problems by solving for unknown variables through a complete set of equations covering the turbine installation. Using similarity laws, model-prototype problems or operation under different conditions can also be tackled. Furthermore, the program is equipped with graphical utilities that include many diagrammatic sketches of reaction turbines, some recommended charts, and the possibility of drawing velocity triangles when corresponding variables are available. The most important feature of the package is an option that allows one to plot the variation of any parameter versus any other one. Through this option, the student can easily understand and discuss the effects of varying design parameters on the overall performance of the machine. Finally, some special features that are important in making the package user-friendly and encouraging-to-use are also available, and the comprehensive example problem provided demonstrates the capabilities of the package as an instructional tool.

Modelling of a Turbocharger Turbine Under Pulsating Inlet Conditions

This paper describes the results of the simulation of a mixed flow turbine under pulsating inlet conditions. The volute casing of the turbine is simulated as a tapered duct with one-dimensional unsteady flow analysis applied to this duct, while one-dimensional steady flow analysis is used in a quasi-steady manner to simulate the flow through the rotor of the turbine. The physical model of the turbine is an improved version of that described by Chen and Winterbone (1), and its predictive capability is evaluated against experimental data of the turbine performance obtained in the Imperial College's unsteady flow turbocharger rig.

Improvement of turbine blade systems to reduce cavitation erosion

1. When designing new runners it is necessary to combine theoretical, experimental, and on-site investigations. 2. Various design modifications of runners were developed for reducing the rate of cavitation erosion of mixed-flow turbines and are being used successfully. The most prospective of them are: a rational form of the blade channel, which makes it possible to completely avoid or minimize cavitation erosion of the rear surfaces of blades in the region of the trailing edge near the lower rim; an increase of the radius of the fillet at the place of joining the leading edge of the blade with the lower rim for high-head runners (H=230–500 m) and moving the lower rim of the runner below the region of high meridian velocities for low-head runners (H=45–100 m) minimized cavitation erosion on the rear surface of the blades near the leading edge and lower rim. 3. Cavitation erosion of runner blades of adjustable-blade turbines can be substantially reduced by rational design of the blades, including the leading and peripheral edges and by machining and finishing the form of the blades on a model.

Investigation of secondary inviscid fluid flows in the runner of a mixed-flow turbine

Investigation of secondary inviscid fluid flows in the runner of a mixed-flow turbine

The aerodynamic loading of radial and mixed-flow turbines

In this paper we investigate the possibility of correlating the aerodynamic loading of radial and mixed-flow turbines in some systematic manner, as is widely done and recognized for axial stages. The loading is shown to be closely related to incidence, and an optimum incidence angle is often calculated from the rotor blade number using centrifugal compressor correlations. It is found that there are many examples of high-efficiency stages which have far fewer blades than these correlations suggest. The relation between blade loading, flow coefficient and isentropic efficiency is investigated in the results of tests on some 40 different turbine stages, and a good correlation is found to exist, with a clearly defined region of best efficiency on a map of loading vs flow coefficients. Various lift and drag coefficients are also defined and calculated for a number of tested turbines, but in general these parameters correlate the data less satisfactorily than the blade loading and flow coefficients. The lift-drag ratio is, however, a useful parameter for optimizing highly loaded stage designs.

Closure to “Discussion of ‘Aeroloads and Secondary Flows in a Transonic Mixed-Flow Turbine Stage’” (1993, ASME J. Turbomach., 115, p. 600)

Closure to “Discussion of ‘Aeroloads and Secondary Flows in a Transonic Mixed-Flow Turbine Stage’” (1993, ASME J. Turbomach., 115, p. 600)

Aeroloads and Secondary Flows in a Transonic Mixed-Flow Turbine Stage

A numerical simulation of a transonic mixed-flow turbine stage has been carried out using an average passage Navier–Stokes analysis. The mixed-flow turbine stage considered here consists of a transonic nozzle vane and a highly loaded rotor. The simulation was run at the design pressure ratio and is assessed by comparing results with those of an established throughflow design system. The three-dimensional aerodynamic loads are studied as well as the development and migration of secondary flows and their contribution to the total pressure loss. The numerical results indicate that strong passage vortices develop in the nozzle vane, mix out quickly, and have little impact on the rotor flow. The rotor is highly loaded near the leading edge. Within the rotor passage, strong spanwise flows and other secondary flows exist along with the tip leakage vortex. The rotor exit loss distribution is similar in character to that found in radial inflow turbines. The secondary flows and nonuniform work extraction also tend to redistribute a nonuniform inlet total temperature profile significantly by the exit of the stage.

A Reliable Tag–Recapture Technique For Estimating Turbine Passage Survival: Application to Young-of-the-Year American Shad (Alosa sapidissima)

A new technique (HI-Z Turb'N Tag, U.S. Patent No. 4,970,988) for estimating turbine passage survival was applied to juvenile American shad (Alosa sapidissima) under three operating conditions at a hydroelectric project. Fish are fitted externally with the Turb'N tag and introduced into turbine penstocks. The Turb'N Tag inflates after turbine passage and buoys fish to the surface for recapture and examination; after removal of tags, fish are held to assess long-term effects. Almost all (96%) test (299) and control (300) fish were recovered; average recovery time was less than 9 min. The overall short-term (1 h) survival of test fish, adjusted for control, was 97%; 24- and 48-h survivals were 98 and 94%, respectively. The 48-h survival of test fish was 98–100% for mixed flow and Kaplan turbines and 66.8% for the mixed flow unit in the vented mode. Acute control mortality was negligible (< 5%). Our technique offers several significant advantages over traditional net recapture methods: applicable to wide range of species and size; allows predetermination of statistically valid sample size, level of significance, and power of the test to determine need for mitigation measures; and estimation of cumulative effects of multiple turbine exposure.

Analytical Optimization Design of Radial and Mixed Flow Turbines

The optimization of radial and mixed flow turbine design, based on simple one-dimensional aerodynamic principles, is described. The objective is to minimize energy losses by reducing the inlet and exit velocities of the rotor. The procedure is based on the specification of a loading coefficient. Previous work has shown that turbines of this type have loading coefficients that lie in a narrow band, and so suitable values can be readily determined. A more detailed specification of losses is unnecessary for the optimization. Optimizations are described for zero and non-zero inlet blade angles, and zero, positive and negative exit swirl conditions.

Design of a Highly Loaded Mixed Flow Turbine

The high boost pressures and fuel–air ratios required for the next generation of turbocharged diesel engines imply an increased turbine expansion ratio without an increase in the speed of rotation. This leads to a requirement for high peak efficiency at lower values of blade speed/isentropic expansion velocity U/C than are normal today. The objective of this project was to achieve this with a mixed flow rotor with a positive inlet blade angle. Two rotors were manufactured and tested: one a ‘constant blade angle’ design and the other a ‘constant incidence’ design. In practice both achieved a peak efficiency at a low U/C value, but the constant blade angle design, at 0.84 total to static efficiency, was significantly more efficient than the constant incidence design at 0.77. These efficiencies are highly competitive, compared to current radial turbine design. It is suggested that the reasons for this difference are a lack of understanding of the incidence and its effects on a mixed flow rotor, and a region of diffusion in the shroud-trailing edge corner of the suction surface, apparently worse for the constant incidence design.

Experience in setting up and operating the units of the Inguri hydroelectric station in a synchronous capacitor regime

1. The experience of adjusting and testing the units of the Inguri hydrostation in a SC regime can be useful for designers determining the need and possibility of using high-head units in this regime. 2. When designing high-head mixed-flow turbines for which a SC regime is provided, it is necessary to take into account the strong pumping action preventing freeing of the runner from water. 3. To provide the minimum consumption of power from the supply during operation in the SC regime, it is necessary to make provisions for a controlled device draining water from the lower zone of the spiral casing for its unloading. 4. For high-head turbines operating in a SC regime, it is necessary to provide a shaft seal unlike the two-row lobed seal, which is not serviceable in the SC regime.

Modification of turbine runner blades at the chirkey hydroelectric station

1. Modification of the runner blades of mixed-flow turbines, as the experience of modifying the turbine runners at the Chirkey hydrostation shows, leads to an increase of the power parameters of the turbines — power and efficiency — which makes it possible to regrade the units to a higher capacity. 2. The positive effect from modifying the runner blades at the Chirkey hydrostation consists in a 10% increase of capacity of the hydrostation; in an increase of efficiency due to a shift of the operating characteristics by 0.5–4% toward larger powers (for loads of the unit of 50% of the nominal and higher); in an increase of efficiency due to an increase of its maximum values at the extremes of the operating characteristics by 0.5–3%. 3. The effect from increasing the efficiency increases with increase of the operating heads of the turbines.

A Finite Element Computer Code to Calculate Full 3-D Compressible Potential Flow in Turbomachinery

A Finite element computer code is presented for calculation of three-dimensional compressible flows in turbomachinery under the steady and potential flow limitations. The method used relies upon a variational statement equivalent to the classical velocity potential formulation of this problem. The solution domain is discretized by using hexahedral superelements each composed of six ten-node tetrahedral elements enabling quadratic interpolation of velocity potential. The code offers the flexibility of choosing a combination of subparametric and isoparametric elements. Application of the code to the Gostelow cascade, an experimental turbine stator, the first stage stator and rotor of an electric utility axial flow turbine and finally to a mixed flow turbine rotor are presented. The validity of the results are established by comparison with the exact solution, experimental data and calculations by other numerical methods.Copyright © 1984 by ASME

Progressive designs in power-engineering plant for hydroelectric and pumped-storage power stations

Solution of the following fundamental problems is required for the further introduction of progressive engineering solutions in the field of hydropower plant design: 1. Development and construction of efficient reversible hydraulic machines, installations for starting them in the pump mode, equipment and systems for automated control and regulation; expansion of investigations aimed at refining elements of the flow-through passages and the block as a whole, thorough study of all static and transient regimes, the starting phenomena of the machine into the pump mode and back, operation of the reversible machine in the synchronous-condenser mode; through study of the work of the electrical-engineering equipment (switches, transformers, circuit breakers et al.) under conditions of frequent starts and stops, the carrying out of proposed studies of the main technological plant of the PSHS, including high-head PSHS of the shaft type. 2. Coping with the unique hydraulic 640 MW turbogenerators at the Sayano-Shushenskoe HES, including carrying out of the necessary series of full-scale investigations; development of a mixed-flow turbine of a new design which combines the functions of both a turbine and a gate, for the Rogun HES (H=318 m, N=3600 MW). 3. Development and further introduction of diagonal-type hydraulic turbines: Coping wisssith DPL-type turbines for the Zeya HES, including carrying out of a series of full-scale tests; manufacture of turbines for the Kolyma HES, currently under construction; a study of the possible use of turbines of this type for the Moka (head, up to 140 m; capacity of set, 260 MW), Middle Enisei and Osinovo (head of 55 m, capacity of set, 500 MW) and other HES, currently in the design stage. 4. Investigations and development of powerful hydraulic turbogenerators involving impulse-type turbines (Pelton wheels), for the Zramag and Dar'yal HES (head 630 m; capacity of set, 180 MW). 5. Further investigations into methods of energy dissipation of flow, development and introduction of optimal layouts of mechanical plant, for heads of up to 200 m and discharge of 1000 m3/sec, with the issue of recommendations for the design of specific HES. 6. Widening of the search for progressive economic solutions in regard to layouts and outlines of turbine units; continuation of studies of the hydraulics of turbine units, including transient and unstabilized phenomena, pressure fluctuations in the flow-through passages, and cavitation phenomena, aimed at raising operational efficiency. 7. Development and introduction of ASU TP HES in PSHS, including development of the necessary gauges.

Computer Aided Design of Mixed Flow Turbines for Turbochargers

The paper describes a comprehensive computer aided design procedure and its use to investigate mixed flow turbines for automotive turbocharger applications. The outside dimensions of rotor and casing as well as blade angles are determined from one-dimensional design and off design calculations, the detailed blade shape from quasi-three-dimensional analysis and mechanical stressing and vibration programs, and geometric data are presented as outside views and sections of the rotor by a graphics subroutine. The procedure consists of a series of separate programs rather than a single program, so that the designer’s intervention at each stage of the process can be applied. Two mixed flow rotors were designed, manufactured and tested in a specially designed high speed dynamometer. The first was intended to achieve a substantial increase in mass flow over the reference radial rotor without loss of efficiency, while the latter was intended as a direct replacement of the reference radial rotor, but should give more favorable pulse performance when operating in conjunction with an engine due to changes in the operating map viz: a) lower tip speeds for best efficiency, and b) flatter mass flow characteristics. Both effects were predicted by analysis and confirmed by tests.