Physics and Control of Flow and Acoustics in Bi-Conical Supersonic Rectangular Twin Jets
Abstract
Jet noise has been an environmental concern since the advent of jet aircraft. The past seven decades have seen much research into understanding and addressing this challenging problem, primarily in commercial aircraft. Jet noise from high performance military aircraft, especially during takeoff and landing on Navy flight decks, has also received growing attention in recent years. The continuous drive to higher specific thrust and agility results in increasing jet noise levels. Compounding this issue is that many military bases, naval in particular, are located in desirable locations on the coasts, and surrounding communities are encroaching closer to these bases, thereby making community noise a significant issue for the military aswell. Scaling analysis over 60 years ago showed that jet noise can be drastically reduced by large by-pass ratio engines. An added advantage of such engines is their improved fuel efficiency. The jet engine industry has fully exploited this concept. However, large by-pass ratio engines are not suitable for high performancemilitary aircraft due to their increased drag penalty and reduced agility.Closely-spaced twin jet engines are commonly used in military aircraft and even some proposed future commercial aircraft designs include two or more engines in close proximity. The near-field pressure and sound of closely-spaced jets interact and the strength and nature of the interaction strongly depend upon the distance between the two jets and the jet operating conditions. In some tactical aircraft, the jets are separated by less than 2 jet diameters causing strong jet-jet interactions. In such cases coupling has resulted in aircraft structural damage as well as significant near-field and far-field pressure and noise amplification. Our recent project with ONR using twin round supersonic jets with military-style converging-diverging nozzlesseparated by two nozzle exit diameters (2D) showed strong interactions between the two jets at certain operating Mach numbers with significantly increased near-field pressure/acoustics and far-field acoustics.The results also showed the tremendous success of plasma-based active flow control to decouple the two jets and reduce near-field pressure/acoustics by up to 6 dB and far-field acoustics by up to 3 dB, as well as adding to our understanding of flow physics and noise sources.Integration of propulsion and aerodynamics in next generation tactical aircraft, especially for naval applications, will require non-axisymmetric (e.g. rectangular) nozzle geometries. In addition to the ease of propulsion and aerodynamic integration, such nozzles provide better thrust vectoring, lower observability,reduced noise, and mixing enhancement/thermal signature reduction. The potential benefit of using rectangular jets in comparison with round jets strongly depends on the nozzle aspect ratio, jet operating regimes, Mach numbers, and temperatures. A three-year experimental effort, with strong collaboration with simulations groups, focused on fundamental understanding and control of dynamics of twin supersonic rectangular heated and unheated jets, is proposed. The proposed design Mach number and aspect ratio are 1.5 and 2, respectively. The proposed total budget is $475,000. The primary objectives of the proposed research are fivefold: (1) to design a military-style (bi-conical) supersonic rectangular twin-jet facility, similar to our earlier design of supersonic round twin-jet facility, that can be easily simulated computationally by collaborators and replicated experimentally by other groups; (2) to carry out detailed flow field and near- and far-field pressure and acoustic measurements in both heated and unheated jets in various operating regimes (over-, fully-, and under-expanded) to better understand flow and acoustic fields in such jets; (3) to use the knowledge gained in part (2) in designing active flow control to alter the flow and acoustic behavior of the jets on-demand to imp
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 24, 2019
- Source ID
- N000141912207
Entities
People
- Mohammad Samimy
Organizations
- Office of Naval Research
- Ohio State University
- United States Navy