Cooled Radial In-Flow Turbines for Advanced Gas Turbine Engines

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.

Use of a Tracer Gas Technique to Study Mixing in a Low Speed Turbine

A method of using a flame ionization detector to study the movement of air containing a small concentration of ethylene is described. Ethylene is chosen because it has almost the same density as air so buoyancy effects are negligible. The technique is applied to flow in a bent duct and in a low speed air turbine. In both cases large scale migrations of the end wall boundary layers onto the suction surfaces are observed. However, in the turbine the span wise movement and mixing of the flow at mid-span is remarkably small.

Gemini T-20G-8 XM1 Tank APU

Auxiliary power is often provided on combat vehicles in the U.S. Army for battery charging, operation of auxiliary vehicle equipment when the main engine is not running, or to provide assistance in starting the main engine in extreme cold weather conditions. The use of a gas turbine for these applications is particularly attractive, due to its small size and lightweight. In November 1978, the U.S. Army Tank-Automotive Research and Development Command, Warren, MI awarded a contract to the Turbomach Division of Solar Turbines International, San Diego, CA, for the development of a 10 kW 28 vdc gas turbine powered auxiliary power unit (APU) for installation in the XM1 main battle tank. This paper describes the general features of the Solar Turbomach T-20G-8 Auxiliary Power Unit, a single-shaft gas turbine driven generator set which has been developed under this contract. This APU is one of the family of Gemini powered APUs and is a derivative of the U.S. Army 10 kW gas turbine engine-driven, 60 and 400 Hz generator sets developed by Solar. The electrical components were newly developed for this particular application. Currently, the APU is in qualification testing both in the laboratory and in the XM1 main battle tank.

New Correlations of the Two-Dimensional Turbine Cascade Aerodynamic Performance

Theoretical evaluation and experimental research have been conducted to verify the performance of steam and gas turbines, including exhaust turbines of superchargers. The simplified channel method and hydroelectrical analog method have been used to calculate blade surface velocity distribution. Based on the “fully developed turbulence” assumption, viscous effects are approximately taken into account by using the boundary layer theory. Theoretical optimum profile loss coefficients are given. Effects of velocity profile on losses are analyzed. Turbine cascades have the characteristics of high solidity, high setting angle and high air turning angle, which facilitate the use of the channel concept. On this basis, K.M. Todd’s “passage convergent gradient,” modified O. Zweifel’s “tangential load coefficient” and other effective criteria have been chosen and cascade data correlated. Some relatively accurate semi-empirical formulas for predicting the aerodynamic performance of cascades are formulated.

Rotor Wake Mixing Effects Downstream of a Compressor Rotor

An experimental study of rotor wake was conducted in the trailing-edge and near-wake regions of a moderately loaded compressor rotor blade using a rotating tri-axial hot-wire probe in a rotating frame of reference. The flow fieldwas surveyed very close to the trailing-edge as well as inside the annulus- and hub-wall boundary layers. The large amount of data acquired during this program has been analyzed to discern the decay effects as well as the span wise variation of three components of velocity, three components of intensities and three components of shear stresses. The data set also include extensive information on the variation of the flow properties downstream. The other derived quantities include wake momentum thickness and deviation angles at various span wise and downstream locations. These data are presented and interpreted, with emphasis on the downstream mixing as well as endwall-wake interaction effects.

A Model for Dynamic Loss Response in Axial-Flow Compressors

An experimentally-determined dynamic loss response function was developed and incorporated in a model to predict the rotating stall behavior of an experimental compressor. The loss response model was developed employing Fourier transforms. The basis of the compressor model is a mathematical representation of the flow fields upstream and downstream of the compressor rotor. The compressor rotor is represented in the model by a semi-actuator disc. The results of the investigation show that the physical mechanisms which control the onset and propagation velocity of rotating stall in a single-stage compressor can be modeled with the use of the loss response function in a semi-actuator disc model of the compressor. The function represents the dynamic loss characteristics of the compressor rotor row, and provides important advantages over previous techniques.

Further Studies of the Influence of Thermal Effects on the Predicted Acceleration of Gas Turbines

A previous study has investigated the effect of changes in compressor characteristics, due to transient heat transfers, on the predicted accelerations of a singles-pool aero gas turbine of pressure ratio 9.5. In the present paper the analysis is extended to a two-spool bypass engine of pressure ratio 21. The increases in the predicted acceleration times of this engine, due to the inclusion of heat absorption and compressor characteristic change, are more marked than with the lower pressure ratio engine, depending on the fuel schedule used. The effects of changes in component efficiencies on predicted acceleration have also been studied. Again, the higher pressure ratio engine shows the greater influence. Compared with thermal absorptions, it is likely that component efficiency changes have as much, if not more effect on predicted accelerations.

Critical Materials: A New Dimension

The decade of the ’80s was ushered in with a new dimension for designers, the availability of, and the meteoric cost increases of key materials. Though cost consciousness has always been a materials selection factor, current rates of increase make selection decisions more critical. Shortages of key metals such as cobalt, titanium, tantalum, molybdenum, and columbium, as well as potential problems with chromium and aluminum force the designer to carefully weigh his decisions. Questions of basic raw materials availability, metal conversion capacity, and the increasing influence of raw materials cost upon product cost must be considered. Vehicular gas turbine engine designers must evaluate materials selection decisions based upon these factors, and accompanying manufacturing processes to minimize input material requirements., Achieving high performance, with the required durability, at an acceptance cost is a bigger challenge than ever. This paper provides a view of the critical material situation and outlook, and typical options that are available.

Inverse or Design Calculations for Non-Potential Flow in Turbomachinery Blade Passages

A new inverse or design calculation procedure has been devised for non-potential flow fields and has been applied to turbomachinery blade row design. This technique uses as input quantities the surface pressure distribution and geometric constraints and may be used for two- or three-dimensional flows as well as inviscid or viscous flows. If a geometry satisfying both the constraints and the pressure distribution cannot be found, a solution satisfying the constraints and a relaxed pressure distribution is found. Calculational examples are presented for inviscid supersonic compressor cascade designs and the extension to three-dimensional flows discussed.

Development of FT9 Marine Gas Turbine

The FT9 Marine Gas Turbine development program was initiated in August 1973 by the Naval Sea Systems Command to fulfill, in part, the requirement for a family of gas turbine engines ranging in power from 1000 to 30,000 hp. The FT9 satisfied the requirement to develop a 30,000 hp class marine gas turbine. The FT9 is a derivative of the Pratt & Whitney Aircraft JT9D engine, which powers Boeing 747, DC-10 and A300 aircraft, and of the FT4 industrial gas turbine engine. The FT9 specification also required development of an on-line engine condition monitoring system. A rigorous development test program showed the FT9 has met all specified U.S. Navy requirements and demonstrated its suitability for use in U.S. Navy combatant ships.