Water, in the liquid or vapor phase, injected at various locations into the gas turbine cycle has frequently been employed to improve engine performance. One such way to improve engine performance is by steam injection, of varied quantity, into the combustor section of the engine. Combustor steam injection increases turbine mass flow rate without increasing airflow rate and consequently increasing the specific power (power/lbm of air). Another approach, receiving widespread acceptance in recent years, is to inject water droplets into the inlet duct upstream of the engine compressor inlet. As the droplets evaporate, prior to entering the compressor, the inlet air is cooled subsequently decreasing compressor power and thus increasing engine power output. The present paper examines the concept of injecting water droplets, termed fogging, in excess of the amount that can be evaporated before entering the engine compressor. This excess water, termed over-spray, is carried directly into the engine compressor. The computer simulated performance of a simple cycle gas turbine engine using evaporative cooling upstream of the compressor with over-spray is reported. The paper describes an improved simulation model developed to predict compressor performance as water is evaporated while passing through the stages of an axial flow compressor. The effects are similar to those of an intercooled compressor without the complications of additional piping, heat exchangers, and the requirement for a dual spool compressor. The results of a parametric study of the effects of evaporative cooling on engine operating characteristics are presented. These results include compressor performance characteristics modified for various inlet conditions (temperature, pressure, and humidity) and fogging conditions (flow rate, over-spray, and water temperature) as well as estimates of the reduced compression work and lowered compressor discharge temperatures. These modified compressor performance characteristics are used in the engine simulation to predict how an over-sprayed engine would perform under various operating conditions. Estimates of increased output power and increased specific power are presented.

Water, in the liquid or vapor phase, injected at various locations into the gas turbine cycle has frequently been employed to improve engine performance while simultaneously reducing NOx emissions. Commercial steam injected gas turbines have been designed to inject small amounts of steam (less than 15% of air flow), generated in a heat recovery boiler, into or downstream of the combustor. Recently, it has been proposed to inject larger amounts of water (as high as 50% of air flow) and operate combustors near stoichiometric conditions. All these methods increase turbine mass flow rate without increasing air flow rate and consequently increase specific power. The increase in specific power for naval applications means smaller intake and exhaust stacks and therefore less impact on topside space. The present paper presents a new concept, in naval propulsion plants, to decrease NOx production and increase specific power with a water fog (droplet spray) injected (WFI) directly into the inlet of the engine compressor. The simulated performance of a simple-cycle gas turbine engine using WFI is reported. The paper describes the computer model developed to predict compressor performance resulting from the evaporation of water passing through the stages of an axial flow compressor. The resulting effects are similar to those of an intercooled compressor, without the complications due to the addition of piping, heat exchangers, and the requirement for a dual spool compressor. The effects of evaporative cooling on compressor characteristics are presented. These results include compressor maps modified for various water flow rates as well as estimates of the reductions in compression work and compressor discharge temperature. These modified compressor performance characteristics are used in the engine simulation to predict how a WFI engine would perform under various water injection flow rates. Estimates of increased output power and decreased air flow rates are presented.

A rotor-mounted radio telemetry instrument system for measuring surface pressures on the rotating blades of an axial-flow compressor was developed and tested. The paper describes the design of the instrument system and several tests to establish its accuracy. Measurements of average and fluctuating surface pressures were reported. Measured pressure levels were found to agree with theory and available experimental data.

The steam-augmented gas turbine (SAGT) differs from commercial steam-injected gas turbines where steam flow may be considerably less than 15% of air flow. SAGT combustors may operate near stoichiometric combustion conditions with steam flow as high as 50% of air flow, thus achieving specific powers exceeding 555 hp-sec/lb. A previous simulation study of the steam-augmented gas turbine, which did not include compressor and turbine maps, examined the applicability of the concept in the Navy’s DDG-51-class ship environment. In this re-examination, component maps were employed to establish credible off-design engine performance, and to confirm estimates of overall ship fuel requirements based solely on anticipated component efficiencies. Also, the present simulation employs a heat-exchanger sub-program fully integrated into the main software program. The re-examination has led to several revisions and refinements of previous conclusions, which are discussed in the text. The SAGT engine concept described herein, dispenses with intercoolers, but adds a low-pressure reheat combustor. The low-pressure combustor flame temperature exceeds 2700° F, which analyses show to be stable. Exhaust gas temperatures are not permitted to fall below 450° F, and the heat recovery steam generator is designed to hold feedwater temperatures close to 300° F to avoid the gas-side acid dewpoint. At the most efficient operating points, the efficiency of this new reheat SAGT engine exceeds 44.5% with a 2200° F turbine inlet temperature, at an ambient 100°-F temperature. Moreover, it exhibits a 23% reduction in overall system volume. Simulation data show that the maximum efficiency of the SAGT engine peaks at engine powers required for cruising speeds, in contrast to the efficiency of the LM2500, which peaks at full-throttle. Since Navy ships operate near cruise conditions for the majority of their mission time, a SAGT plant uses 29% less fuel than the baseline LM2500 plant. Moreover, employing conservative cost estimates, the SAGT plant is quite competitive on a first-acquisition cost basis with gas turbines currently in the fleet.

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.