Partial Admission Turbine Research Articles

Full- and Partial-Admission Performance of a Simplex Turbine

The turbines used in rocket-engine applications are often partial-admission turbines, meaning that the flow enters the rotor over only a portion of the annulus. These turbines have been traditionally analyzed, however, assuming full-admission characteristics. This assumption enables the simulation of only a portion of the 360-deg annulus with periodic boundary conditions applied in the circumferential direction. Whereas this traditional approach to simulating the flow in partial-admission turbines significantly reduces the computational requirements, the accuracy of the solutions has not been evaluated or compared to partial-admission data. In the current investigation, both full-admission and partial-admission three-dimensional unsteady Navier-Stokes simulations were performed for a partial-admission turbine designed and tested at NASA Marshall Space Flight Center. The results indicate that the partial-admission nature of the turbine should be included in simulations to properly predict the performance and flow unsteadiness of the turbine.

Estimation of Convective Heat Transfer Coefficients in Industrial Steam Turbines

Steam turbines are increasingly being used in industries for duties other than base load operations, where fast start-ups, rapid load changes, and frequent shutdowns are involved. Generally, industrial steam turbines operate with constant inlet steam parameters and are partial admission turbines having the first turbine stage as an impulse stage and the subsequent turbine stages as reaction stages on drum-type rotors. During start-up, as control valves open, steam is admitted and passes through impulse blading, wheel chamber, and through the subsequent reaction stages. The turbine outer casing is horizontally split and the parting plane flanges have relatively thick sections. To limit thermal stresses which arise due to temperature differences in outer casings and rotors, the steam flow has to be increased gradually. The rate at which the steam flow is to be increased depends on the efficiency of heat transfer, i.e., the heat transfer coefficient, and hence knowledge of inside heat transfer coefficient is essential. The high heat transfer coefficients, h, at the beginning of cold start are attributable to condensation of steam at initial stages. The value of h decreased with lapse of time, and also its variation reduced considerably over time. Further, the h value varies more with more » location rather than with lapse of time. The variations observed in h show the complexity of heat transfer process and also bring out the fact that semi-empirical formulas, such as Gazley`s (1958), are not accurate for application in steam turbines. More studies need to be conducted on models of steam turbines to generate adequate data based on which a new correlation for the heat transfer coefficient h for start-up phase of operation could be proposed. « less

Pulse Converters—A Method of Improving the Performance of the Turbocharged Diesel Engine

Today, most turbocharged diesel engines operate on the pulse system. This is most effective on those engines whose exhaust manifolds can connect groups of three cylinders to a turbine entry without scavenging interference, e.g. three-, six-, nine- and twelve-cylinder engines. However, when only two cylinders can be connected to each turbine entry, e.g. four-, eight- and sixteen-cylinder engines, without interference, the system is usually less efficient. This is because the widely fluctuating, partial admission turbine conditions lower the average turbine efficiency. Recently, the pulse converter has been developed to improve the performance of such engines. A detailed investigation into the operation and application of the pulse converter has been conducted. Test results from three completely different types of engines showed substantial improvements in performance. The dependence of the pulse converter on engine speed and load, the effect of area variations in the pulse converter and the timing of the interfering exhaust pressure waves have been studied. A comparison of theoretically predicted and measured transient pressures (from a model pulse converter fitted to a pulse generator) was made. The theoretical analysis is based on empirical steady-flow loss coefficients and forms a boundary condition for a method of characteristics analysis. Results are compared with those predicted by the simple constant-pressure theory.

Pulse Converters—A Method of Improving the Performance of the Turbocharged Diesel Engine

Today, most turbocharged diesel engines operate on the pulse system. This is most effective on those engines whose exhaust manifolds can connect groups of three cylinders to a turbine entry without scavenging interference, e.g. three-, six-, nine- and twelve-cylinder engines. However, when only two cylinders can be connected to each turbine entry, e.g. four-, eight- and sixteen-cylinder engines, without interference, the system is usually less efficient. This is because the widely fluctuating, partial admission turbine conditions lower the average turbine efficiency. Recently, the pulse converter has been developed to improve the performance of such engines. A detailed investigation into the operation and application of the pulse converter has been conducted. Test results from three completely different types of engines showed substantial improvements in performance. The dependence of the pulse converter on engine speed and load, the effect of area variations in the pulse converter and the timing of the interfering exhaust pressure waves have been studied. A comparison of theoretically predicted and measured transient pressures (from a model pulse converter fitted to a pulse generator) was made. The theoretical analysis is based on empirical steady-flow loss coefficients and forms a boundary condition for a method of characteristics analysis. Results are compared with those predicted by the simple constant-pressure theory.

Some tests on partial admission turbine cascades

The cascade tests described in this paper were performed to investigate the nature of flow in the rotor blade channels of axial flow turbines with partial admission. Three cascades of different pitch-chord ratios were tested for this purpose. The variation of the tangential force on the cascade for various positions was measured and compared with Stenning's analysis; the agreement between this analysis and the test points is good. The tests show that the tangential force on the cascade increases with the Reynolds number within the range ( 0·82 × 10 5 to 1·38 × 10 5 ) covered by the experiments. Direction and velocity profiles obtained behind the cascade at both ends of the sector showed the difference between the flows in the turbine blade cascades with full and partial admissions. Pressure distribution around the blades at both ends of the admission sector showed a marked departure from the normal full admission pattern. Measurement of the static pressure in the clearance space between the cascade and the inlet duct at the ends of the admission sector indicated the presence of “suction” which varied with the position of the cascade relative to the admission sector.

Aerodynamic losses in partial admission turbines

A theory for the determination of the aerodynamic losses in a flat-bladed rotor operating under partial admission conditions is taken from a previous paper. It is adapted to obtain a formula for the loss coefficients for a real turbine rotor operating under partial admission conditions. An approximate but much simplified version of this formula is developed for certain cases. The loss formulae derived are verified using three turbine rotors of different blade pitch. The formulae are shown to be approximately correct and the effect of blade pitching is shown to be negligible. A method (numerical example) of predicting the stage efficiency of partial admission turbines is also given.

The Formation of a Shock Wave in a Blade Passage of a Partial Admission Turbine

The problem of unsteady flow in the blade passage of a partial admission impulse turbine with supersonic nozzle flow is introduced. Previous work carried out at M.I.T. revealed the presence of a shock wave at the entrance to the blade passages and this report sets out to predict the formation of such a shock wave using a one-dimensional theory. The one-dimensional theory is discussed in some detail and a novel method for dealing with the inflow boundary conditions is developed. Details of a characteristic calculation are given, and this is matched with a shock wave analysis to predict the formation of the shock wave. The implications of the theoretical work are discussed and experimental results obtained from a hydraulic analogy are presented which confirm the analysis.

Axial Turbine Performance Evaluation. Part A—Loss-Geometry Relationships

Generalized loss correlations for full and partial admission turbines have been derived and critically compared with recently published data. Effects included are Reynolds number, blade angles, blade height, blade number, blade trailing edge thickness, tip clearance, and reaction. These generalized loss relationships are for use in optimization of turbines over a wide range of possible operating conditions.

Axial Turbine Performance Evaluation. Part B—Optimization With and Without Constraints

The maximum obtainable efficiency and associated geometry have been calculated based on the use of generalized loss correlations from Part A and are presented for full and partial admission turbines over a wide range of specific speeds. The calculated effects of varying values of Reynolds number, tip clearance, and trailing edge thickness on turbine performance are presented. Because of the anticipated difficulty in fabricating some of the optimum geometries calculated, the effects of using nonoptimum values of geometric parameters on attainable efficiency have also been investigated. The derating factor for machine Reynolds number is shown to be a strong function of specific speed, varying from 0.96 at a specific speed of 100, to 0.6 at a specific speed of 3, when Reynolds number is 105 compared to a reference value of 106. The derating factor for tip clearance is shown to be similar to what would be expected if the clearance area were considered as a leakage area. The use of blade heights, blade numbers, rotor exit angles, and degrees of reaction varying from the optimum by 25 percent produce maximum derating factors of 0.99, 0.98, 0.985, and 0.97, respectively, when compared to full optimum values.

Partial-Admission Turbines

Partial-Admission Turbines

Closure to “Discussions of ‘The Hydraulic Analogy Applied to Nonsteady, Two-Dimensional Flow in the Partial-Admission Turbine’” (1961, ASME J. Basic Eng., 83, pp. 420–421)

Closure to “Discussions of ‘The Hydraulic Analogy Applied to Nonsteady, Two-Dimensional Flow in the Partial-Admission Turbine’” (1961, ASME J. Basic Eng., 83, pp. 420–421)

The Hydraulic Analogy Applied to Nonsteady, Two-Dimensional Flow in the Partial-Admission Turbine

The Hydraulic Analogy Applied to Nonsteady, Two-Dimensional Flow in the Partial-Admission Turbine

Analysis of Partial Admission Axial Impulse Turbines

Presented herein is a review of the analysis and design of axial partial admission turbines. The analysis utilizes the similarity concept of specific speed and specific diameter. The result of the analysis is presented in design charts which show efficiency lines and optimum geometric ratios as a function of the design parameters, specific speed and specific diameter for certain regimes of Reynolds number and Mach number. The validity of the analysis is substantiated by test data.