Robert Clark
(Advisor: Prof. Dimitri Mavris)

will defend a doctoral thesis entitled,

A Method for the Conceptual Design of Integrated Variable Cycle Engines and Aircraft Thermal Management Systems

On

Friday, November 17th at 8:00 a.m.
Weber SST CoVE
Click here to join the meeting

Abstract
Current and future military fighter aircraft are tasked with fulfilling strenuous requirements, many of which are at odds with each other. An increased demand for high power electronics and weapons systems has put the need for auxiliary power generation and heat dissipation on par with the more traditional fighter aircraft requirements of extended range, speed, stealth, and maneuverability. All of these requirements can be traced back in some way to the propulsion system, which is arguably the single most important subsystem on the aircraft. For decades, the mixed-flow turbofan (MFTF) has been the propulsion system architecture of choice for fighter aircraft. However, the demands placed on modern propulsion systems have highlighted the limitations of the MFTF, and have led to the development of the variable cycle engine (VCE) as a means to improve propulsion system and aircraft performance.

Variable cycle engines show promise in increasing thrust, reducing fuel consumption, and improving heat dissipation capability. A key feature of variable cycle engines is the presence of variable geometry components inside the engine, the positions of which can be modulated to adjust the operating cycle of the engine as operating conditions and demands change. Meanwhile, the aircraft thermal management system (TMS) is tasked with dissipating all of the waste heat on the aircraft and interacts with the propulsion system in a highly coupled manner. The objective of this research was to develop a design methodology at the conceptual design level that improves the design process for integrated variable cycle engines and aircraft thermal management systems.

Cycle analysis can be reduced to finding the roots of a large system of equations. In addition, it can be shown that variable geometry positions act as free variables present in this system of equations. A review of the literature found that existing design methods for variable cycle engines resort to computationally expensive nested optimization routines in order to determine the optimum positions for variable geometry features. Furthermore, the existing literature does not adequately address the coupling effects associated with integrating thermal management systems into the design of a variable cycle engine. A series of research questions, hypotheses, and experiments were developed in order to improve the design process for integrated variable cycle engines and thermal management systems.

To reduce the computational burden of VCE design, a method for building variable geometry schedules was developed that significantly reduces the number of optimizer calls required to evaluate off-design performance of a VCE across a full flight envelope. It was then demonstrated that these schedules could be incorporated directly into the engine design process, eliminating the need to include variable geometry positions in the list of engine design variables to be optimized in an overall engine optimization study. Lastly, it was demonstrated that accounting for the coupling effects between the TMS and VCE during the conceptual design phase enables the cycle designer to capture changes in the optimum engine cycle as thermal management requirements change. Understanding these coupling effects allows the cycle designer to make informed trades between competing mission requirements during the conceptual design phase. The overall VCE/TMS design methodology was demonstrated in a case study that designed a variable cycle engine for a notional fighter aircraft similar to the F-35.

Committee

• Prof. Dimitri Mavris – School of Aerospace Engineering (advisor)
• Prof. Jechiel (Jeff) Jagoda – School of Aerospace Engineering
• Prof. Graeme Kennedy – School of Aerospace Engineering
• Dr. Jimmy Tai – School of Aerospace Engineering
• Dr. Eric Hendricks – NASA Glenn Research Center