Aircraft Engine Noise Reduction Technology
Abstract
There is a growing need to reduce significantly the noise generated by high performance, supersonic military aircraft. The noise generated by military aircraft has direct impact on community noise and on ground and pilot and ground crew well-being. U.S. and international noise regulations will have an impact on the operations and training unless effective steps are taken to reduce the noise. A distinct difference between civilian aircraft engines and advanced military aircraft engines is that military engines tend to have low bypass ratios and high velocities, and thus their noise tends to be dominated by jet exhaust noise. During takeoff or landing, the exhaust from these engines tends to be non-ideally expanded. This proposal is focused on noise reduction techniques at overexpanded (take-off) and design (cruise) operation. Passive noise mitigation devices such as chevrons are being implemented in military jets but they cause performance penalty. Alternatively, there were attempts touse fluidic injection to achieve noise reduction because they can be turned off when not needed, but in older generation engines the lack of available air source to be used for fluidic injection rendered this method impractical. It is expected that the next generation of engines for high-performance military aircraft will incorporate three-stream to improve efficiency and performance. This third stream, or alternatively cooling air, can provide a source for air powered active flow control systems as we propose here. Fluidic control has been tested primarily in circular jets. However, the architecture of modern supersonic airplanes requires integration of the propulsion system with the airframe. Such embedded propulsive system dictates non-circular exhaust nozzles with elongated shapes such as rectangular configurations with various aspect ratios. The impact of fluidic control on non-circular jets has been less investigated and this is one of the motivations for the current proposal. Another aspect of this proposal is addressing modern supersonic airplanes that have two or more engines near each other. The supersonic exhaust jets can interact with each other and impact their acoustic emissions. The interaction between two jets depends on many parameters including the nozzle shape and aspect ratio, separation distance, splay angle, NPR, and NTR. A major goal of this proposal is to acquire thorough understanding of the flow and acoustic behavior of single and twin jets of different aspect ratios and develop design rules that will consider all the relevant parameters and will lead to effective strategies of noise reduction. The project will focus on three efforts: (1) Develop database of the flow and acoustic characteristics of single and twin square, trapezoidal and low aspect ratio rectangular jets with internal fluidic injection for application to next generation propulsion systems. The study will serve to understand their screech characteristics and their interaction. This will be used as a baseline for comparison with the next tasks; (2) Study the impact of continuous and pulsed fluidic injection on screech and interaction between twin jets at cold and hot conditions; (3) Study the impact of micro vortex generators (MVGs) on screech and interaction between twin jets at cold and hot conditions. Additive manufacturing provides the opportunity to fabricate complex geometries. This enables to triage promising configurations and optimize them in a short time and low cost. The proposed research will provide a wide data base for validation of the parallel LES computational studies performed at Stanford University and NRL and will be coordinated with them. Companion proposal is submitted by Stanford University providing details regarding their computational efforts. We have been collaborating with NRL and Stanford University and have published several research papers together.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 13, 2024
- Source ID
- N000142412372
Entities
People
- Ephraim Gutmark
Organizations
- Office of Naval Research
- United States Navy
- University of Cincinnati