Full-Scale Turbofan Demonstration of a Deployable Engine Air-Brake for Drag Management Applications
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Full-Scale Turbofan Demonstration of a Deployable Engine Air-Brake for Drag Management Applications The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Shah, Parthiv N., Gordon Pfeiffer, Rory Davis, Thomas Hartley, and Zoltán Spakovszky. “Full-Scale Turbofan Demonstration of a Deployable Engine Air-Brake for Drag Management Applications.” Volume 1: Aircraft Engine; Fans and Blowers; Marine (June 13, 2016). As Published http://dx.doi.org/10.1115/GT2016-56708 Publisher ASME International Version Final published version Citable link http://hdl.handle.net/1721.1/116098 Terms of Use Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. Proceedings of ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition GT2016 June 13 – 17, 2016, Seoul, South Korea GT2016-56708 FULL-SCALE TURBOFAN DEMONSTRATION OF A DEPLOYABLE ENGINE AIR- BRAKE FOR DRAG MANAGEMENT APPLICATIONS Parthiv N. Shah Zoltán Spakovszky Gordon Pfeiffer Thomas Hartley Massachusetts Institute of Rory Davis Williams International Technology ATA Engineering, Inc. Walled Lake, MI, USA Cambridge, MA, USA San Diego, CA, USA ABSTRACT additional external airframe drag to increase the conventional This paper presents the design and full-scale ground-test glideslope from 3 to 4.3 degrees, with about 3 dB noise demonstration of an engine air-brake (EAB) nozzle that uses a reduction at a fixed observer location. deployable swirl vane mechanism to switch the operation of a NOMENCLATURE turbofan’s exhaust stream from thrust generation to drag Nozzle exit area generation during the approach and/or descent phase of flight. A8 The EAB generates a swirling outflow from the turbofan ANOPP (NASA’s) Aircraft NOise Prediction Program exhaust nozzle, allowing an aircraft to generate equivalent drag Aref Reference area in the form of thrust reduction at a fixed fan rotor speed. The BPF First blade-passing frequency drag generated by the swirling exhaust flow is sustained by the Cd,eq Equivalent drag coefficient strong radial pressure gradient created by the EAB swirl vanes. D Drag Such drag-on-demand is an enabler to operational benefits such F Thrust as slower, steeper, and/or aeroacoustically cleaner flight on Fg Gross thrust approach, addressing the aviation community’s need for active Fn Net thrust and passive control of aeroacoustic noise sources and access to Fnc Net corrected thrust confined airports. FTPR Fan tip pressure ratio Using NASA’s Technology Readiness Level (TRL) M Mach number definitions, the EAB technology has been matured to a level of Fan rotational speed 6, i.e., a fully functional prototype. The TRL-maturation effort N1 involved design, fabrication, assembly, and ground-testing of N1C Fan corrected rotational speed the EAB’s deployable mechanism on a full-scale, mixed- N2C High-spool corrected rotational speed exhaust, medium-bypass-ratio business jet engine (Williams OASPL Overall SPL International FJ44-4A) operating at the upper end of typical SLS Sea-level static conditions approach throttle settings. The final prototype design satisfied a SPL Sound pressure level set of critical technology demonstration requirements that TSFC Thrust-specific fuel consumption included (1) aerodynamic equivalent drag production equal to Vapp. Approach velocity 15% of nominal gross thrust in a high-powered approach W Aircraft weight throttle setting (called dirty approach), (2) excess nozzle flow Wac Corrected air flow rate capacity and fuel burn reduction in the fully deployed Wfc Corrected fuel flow rate configuration, (3) acceptable engine operability during Glideslope angle dynamic deployment and stowing, (4) deployment time of 3–5 Freestream density seconds, (5) stowing time under 0.5 second, and (6) packaging of the mechanism within a notional engine cowl. For a typical twin-jet aircraft application, a constant-speed, steep approach analysis suggests that the EAB drag could be used without 1 Copyright © 2016 by ASME Downloaded From: http://proceedings.asmedigitalcollection.asme.org/ on 04/11/2018 Terms of Use: http://www.asme.org/about-asme/terms-of-use INTRODUCTION thus adversely impacting noise and landing distance, drag Takeoff and approach are the two events responsible for generation should not degrade high-lift performance. Reducing aircraft community noise exposure. Takeoff is dominated by landing distance (i.e., short-field performance) is a competitive noise from the engine at high power, while on approach advantage, particularly for business jets whose owners demand airframe noise competes with and often exceeds engine noise convenience [14]. due to the aerodynamic exposure of structures such as landing The engine’s thrust on approach opposes the additional gear, high-lift devices, control surfaces, and speedbrakes [1], drag being sought in these scenarios. A seemingly simple [2]. These structures all generate drag, which contributes to the solution would be to propose to greatly reduce power to aircraft’s force balance—but their noise typically scales with engines during approach, but this is constrained by the flight speed to an exponent between 5 and 6. This motivates the requirement of a minimum spool-up time to ensure safe go- need for “quiet” drag devices that may be deployed on around during aborted landings [15], [16]. approach to reduce noise through flight paths that are slower, Additionally, during descent in icing conditions, engines aerodynamically cleaner, or steeper (thereby distancing the run at higher fan rotor speeds (N1) to deliver anti-ice bleed air, sound source from the community). and the associated excess thrust may lengthen the duration of Operational methods to reduce community noise have descent and cause excess fuel burn. Such scenarios make come into focus in the last two decades [3], with significant energy management on descent an important topic, especially effort placed on the development of steeper and/or slower for low-drag aircraft such as modern business jets [17]. descent and approach trajectories for noise reduction. Typical The present work is focused on drag generation through transport aircraft glideslopes are around 3 degrees unless thrust reduction using a deployable—and rapidly stowable— modified by local requirements, but steeper descent maneuvers device called an engine air-brake (EAB). A figure of merit for and their potentially beneficial impact on noise have gained EAB performance is “equivalent drag,” which is the engine net interest in recent years. Antoine and Kroo [4] estimated the thrust reduction achieved by swirling the bypass stream noise reduction of a steep approach of 4.5 degrees to be as exhaust. Equation 1 defines the equivalent drag coefficient as much as 7.7 dB. Filippone simulated the A310 [5] and this thrust reduction at fixed N1, normalized by approach determined that up to 6.0 dB noise reduction could be achieved dynamic pressure and a reference area. from increases in both maximum lift and zero-lift drag, and he concluded that further investigation was needed into devices ∆ that increase the nonlifting portion of drag without affecting the , high-lift system. 1 2 Equation 1 2 ∞ Aircraft noise is regulated globally by the International 1 Civil Aviation Organization (ICAO), but it is often increasing Fixing of the fan rotor speed addresses the go-around local requirements that dictate key elements of the design of requirement in the case of a missed approach, provided the aircraft for lower noise. Influential airport authorities will device can be stowed on a timescale much shorter than the continue to push for enabling technologies for noise reductions. typical 8 second spool-up required in FAR 25 [15]. It also Significant successes on continuous-descent approaches ensures that the anti-icing requirement is satisfied during (CDAs) [6], [7] have brought these procedures into more descent in inclement weather. frequent use. London Heathrow (LHR) Airport’s 2015 Constant-speed, steep approach provides a simple way to “Blueprint for Noise Reduction” [8] includes both a campaign assess quiet drag device impact. For small glideslope angles, , for quiet approaches focused on CDAs and exploration of the force balance in the direction of flight equates the weight steeper angles of descent as two of its top ten practical steps to component (Wsin) with the aircraft drag (D) minus engine net cut noise. thrust (Fn). Assuming a fixed aircraft aerodynamic A quiet drag device may enable greater access to configuration, the airframe’s baseline lift, drag, and noise geographically confined airports. The 2006 Airbus A318 steep remain unchanged. The small angle approximation gives approach certification for London City (LCY) Airport was sin, so doubling the aircraft’s glideslope to an angle 2 developed for competitive advantage, allowing the aircraft to requires an additional component of drag (or thrust reduction) be marketed as a regional jet replacement [9]. The drag equal to Wsin.So, for example, to perform a 6 degree management procedure required simultaneous use of high-lift, approach at constant speed requires an drag addition of about high-drag flaps and lift-spoiling high-drag speed brakes, since 5% of the aircraft’s landing weight relative to the 3 degree neither device could generate sufficient drag alone. The baseline. Assuming the additional drag required to fly the steep resulting higher approach