Future Trends in Aircraft Engine Noise Research

The high bypass ratio engines being introduced into service have generally been acknowledged to provide significant improvement in noise abatement. Substanital improvements in future designs will require research into several areas of engine-component noise generation. Low-noise standards also will be influenced by the aircraft mission requirements that affect selection of the power-plant cycle. Each mission requirement presents special noise problems, which must be solved. This paper explores the relationships among aircraft mission requirements, noise research in process at Pratt & Whitney Aircraft, and trends predicted for future research.

Generalization of Experimental Data for Compressor Cascades at Low Speeds

The author compares three different approaches for generalization of experimental data for two-dimensional compressor cascades at low speeds: generalization for maximum value of lift-drag ratio, generalization for maximum cascade quality, and generalization for minimum loss coefficient. Some results given, of comparison for incidence and deviation angles, solidities, and loss coefficients, show the largest difference to be for incidence angles and loss coefficients. Influence of isentropic exponent on the airfoil pressure distribution and cascade losses is considered.

Results of Experiments for Determining the Influence of Blade Profile Changes and Manufacturing Tolerances on the Efficiency, the Enthalpy Drop, and the Mass Flow of Multi-Stage Axial Turbines

When gas and steam turbines are in use, the blade profiles can be thinned by corrosion or erosion and thickened under the influence of deposit formation, thus causing a reduction in efficiency and lifetime. During the production of turbine blades, it is possible that the profiles often become thinner or thicker than the given specified profiles, also causing a decline in efficiency. In addition, the production costs of turbine blades are, to a considerable extent, dependent on the manufacturing tolerances. This report details the effects of thinning and thickening of the profiles on the efficiency, the drop, and the mass flow of multi-stage axial turbines.

The Potential of the Gas-Turbine Vehicle in Alleviating Air Pollution

The author examines the potential of the gas turbine in alleviating air pollution as a replacement for presently used vehicular reciprocating engines. Automobiles receive particular emphasis because of the magnitude of their contribution to the problem. Emissions of gas-turbine engines are compared with those of gasoline reciprocating engines, and other important characteristics relevant to the problem (such as engine power output, reliability, transmissions, vehicle performance, fuel consumption, and manufacturing cost) are discussed. It is concluded that widespread adoption of vehicular gas-turbine engines can — provided these engines can be produced and operated at costs competitive with those of future reciprocating engines — can virtually eliminate automotive air pollution as a source of serious environmental concern.

The Sound of Gas-Turbine Installations

In this overall review of gas-turbine sound and its control, the author discusses the variety of installations, the scope of the noise control problem, criteria, industry performance, noise specifications, and noise measurements. In particular, the magnitude of the noise control problem is indicated by discussion of the sound of an unmuffled 20 Mw turbine. Typical sound pressure level data on current installations are given, and suggestions are made for noise control criteria in the low frequency range.

Aerodynamic Development of a Radial Compressor for a 10-kw Turboalternator

The aerodynamic development of a small high-speed radial compressor for the US Army 10-kw turboalternator is discussed, including initial performance deficiencies arising from blade contour discrepancies. Design performance requirements were attained by correcting these discrepancies and subsequently were exceeded with further geometry refinements. Aerodynamic testing included an investigation concerning the effect of shroud axial clearance on compressor performance and showed that abradable shrouds are desirable for small compressors.

Gas-Turbine Loading Schedule for Maximum Life of the Hot Gas Path Components

The paper describes development of a computational procedure for determining the optimal firing temperature schedule during loading of the gas turbine. It is assumed that the temperature has to be increased in a pre-determined time in a way that will minimize thermal fatigue deterioration of the turbine hot gas path elements. The gas temperature is constrained to lie between certain time-dependent limits all through the transient. The maximum plastic strain in a given loading process is taken as a measure of parts deterioration. The calculations performed are for hollow, stationary airfoils of a gas turbine, but the method is easily adaptable to full profiles and rotational airfoils as well as non-turbine applications where temperature is to be altered while thermal shock is to be minimized. A numerical example is given for illustration of the method.

On the Noise From Jet Diffusers

This investigation has shown that the addition of diffusers of various lengths with a fixed cone angle to a fixed diameter circular jet nozzle increases the noise generation when delivering the same mass flow rate. For the diffusers investigated, the far field SPL was increased with increased diffusion. Also, increased diffusion decreased the directional variation of the SPL in the far field and moved the axial position of maximum noise generation closer to the jet exit. For the longest diffuser investigated, there was considerable noise contribution from the boundary layer inside the diffuser.

Utility Applications for Advanced Gas Turbines to Eliminate Thermal Pollution

Increases in electric power demand during the next 30 years will sharply increase water requirements for condenser cooling and will stimulate the search for alternative solutions to the thermal pollution of our waters. Continuing engineering advances, achieved during extensive research and development efforts on military and commercial gas-turbine applications, could provide the basis for substantially improved power plants that could significantly alleviate thermal pollution. The authors describe the results of analytical studies to estimate the design technology, performance, and cost characteristics of future fossil- and nuclear-fueled gas-turbine power generation systems and the potential for eliminating thermal pollution.

Some Results of Recent Research on Fan and Jet Noise

A 6-ft-dia low-speed fan designed for low-noise production was tested to provide data on noise generation, suppression effects of acoustic treatment, and exhaust jet noise. Preliminary results showed that the overall noise varied with the 5.5 power of the fan speed but was independent of blade loading obtained by varying back pressure at constant speed. The low-velocity jet from the fan produced noise that followed the eighth power law and was lower than predicted by extrapolation of the SAE curve. Modifying the SAE method to eliminate the effects of jet density greatly improved the agreement between prediction and data.