The choice of how to represent the performance of the fans and compressors of a gas turbine engine in a whole-engine performance model can be critical to the number of iterations required by the solver or indeed whether the system can be solved. This paper therefore investigates a number of compressor modelling methods and compares their relative merits. Particular attention is given to investigating the ability of the various representations to model the performance far from design point. It is noted that, for low rotational speeds and flows, matching on pressure ratio will produce problems, and that efficiency is a discontinuous function at these conditions. Thus, such traditional representations of compressors are not suitable for investigations of starting or windmilling performance. Matching on pressure ratio, Beta, the Crainic exit flow function and the true exit flow function is investigated. The independent parameters of isentropic efficiency, pressure loss, a modified pressure loss parameter, specific torque, and ideal and actual enthalpy rises are compared. The requirements of the characteristic choice are investigated, with regard to choosing matching variables and ensuring that relationships are smooth and continuous throughout the operating range of the engine.

A new concept in aircraft propulsion is described in this paper. A variable cycle jet engine is being investigated for a supersonic STOVL aircraft. The engine is the selective bleed turbofan, a two shaft three compressor engine. At low flight speeds this engine operates as a medium bypass turbofan, and for the supersonic cruise condition it operates as a low bypass ratio turbofan in the dry mode. In this paper, the performance of the engine and some of the components is analysed. Off-design engine performance characteristics are explained, compressor running lines are shown, and variable geometry requirements are described. The performance analysis shows that fuel savings are significant, thus reducing aircraft take-off weight. The major advantage of this engine is that all the components are employed all the time, for all operating modes, thus incurring low weight penalties.

No abstract

Typically, crude oil production in Nigeria always accompanied by surface production of associated gas. With little associated gas recovery facilities in place, majority of associated gas is continuously flared with few portions re-injected into the reservoir for enhance oil recovery (EOR). In addition to environmental hazards, wasting substantial amount of produced associated gas is deemed detrimental to a country currently generating less than 54% of its electric power requirement. Onsite power generation as one of the many means of utilization of associated gas has been conceived. Conversely, the availability and performance of the gas turbine engine for onsite associated gas utilization requires evaluation owing to variations in associated natural gas composition globally and the dependency of associated gas production on reservoirs and oil production activities. This paper presents an analytical investigation of gas turbine engine inspired by GE LMS100 frame engine for onsite utilization of associated gas in Nigeria. Gas turbine performance results are presented and performance parameters are compared against typical commercial natural gas grade.

The paper describes a general program which has been developed for the prediction of the transient performance of gas turbines. The program is based on the method of continuity of mass flow. It has been applied successfully to a wide range of aero gas turbines, ranging from single to three-spool and from simple jet to bypass types with or without mixed exhausts. The results for three of these engine types are illustrated. Computing times are reasonable, increasing with the complexity of the engine. A parallel paper describes the inclusion of thermal effects in the prediction program.