energies Article Modelling a Hypersonic Single Expansion Ramp Nozzle of a Hypersonic Aircraft through Parametric Studies Andrew Ridgway, Ashish Alex Sam * and Apostolos Pesyridis College of Engineering, Design and Physical Sciences, Brunel University London, London UB8 3PH, UK; [email protected] (A.R.); [email protected] (A.P.) * Correspondence: [email protected]; Tel.: +44-1895-267-901 Received: 26 September 2018; Accepted: 7 December 2018; Published: 10 December 2018 Abstract: This paper aims to contribute to developing a potential combined cycle air-breathing engine integrated into an aircraft design, capable of performing flight profiles on a commercial scale. This study specifically focuses on the single expansion ramp nozzle (SERN) and aircraft-engine integration with an emphasis on the combined cycle engine integration into the conceptual aircraft design. A parametric study using computational fluid dynamics (CFD) have been employed to analyze the sensitivity of the SERN’s performance parameters with changing geometry and operating conditions. The SERN adapted to the different operating conditions and was able to retain its performance throughout the altitude simulated. The expansion ramp shape, angle, exit area, and cowl shape influenced the thrust substantially. The internal nozzle expansion and expansion ramp had a significant effect on the lift and moment performance. An optimized SERN was assembled into a scramjet and was subject to various nozzle inflow conditions, to which combustion flow from twin strut injectors produced the best thrust performance. Side fence studies observed longer and diverging side fences to produce extra thrust compared to small and straight fences. Keywords: scramjet; single expansion ramp nozzle; hypersonic aircraft; combined cycle engines 1. Introduction Hypersonic flight is considered the next great advancement within the aviation industry. In recent years there has been an increase in demand for commercial supersonic and hypersonic travel as aerospace companies have been looking to replace long haul subsonic flights with hypersonic aircraft designs that could be economically and environmentally viable. More aerospace companies are investing in new engine technologies and developing concept aircraft designs capable of supersonic and hypersonic travel. Even though this has been investigated for over half a century, there have been only few breakthroughs which have made hypersonic flight available on a commercial level. This is mainly due to the challenges ranging from structural demands, fuel economy, maintenance issues, direct operating costs, and supersonic combustion. The most successful supersonic commercial airliner was the Concorde which cruised at Mach 2. Concorde’s retirement in 2003 was a combination of inflated fuel prices and the infamous accident in which 113 people lost their lives. The loss of confidence in the safety of the aircraft was the same reason for the Tupolev Tu-144’s early retirement, the only other commercial supersonic aircraft equivalent to the Concorde. Hypersonic vehicles have been around for several decades but have never been utilized for commercial aviation. Rocket-powered vehicles were the main bearers of hypersonic flight as, they would propel vehicles beyond the atmosphere and exploit gravity to re-enter the atmosphere, achieving Energies 2018, 11, 3449; doi:10.3390/en11123449 www.mdpi.com/journal/energies Energies 2018, 11, x FOR PEER REVIEW 2 of 29 achieving phenomenal speeds of up to Mach 36. The V-2 rocket, designed by Germany, flew at five timesEnergies the2018 speed, 11, 3449of sound, the first vehicle to be considered hypersonic. Other vehicles to have2 offlown 29 at hypersonic speeds are intercontinental ballistic missiles, Apollo space capsules, the space shuttle, and the experimental X-planes [1]. There has never been a hypersonic commercial aircraft phenomenal speeds of up to Mach 36. The V-2 rocket, designed by Germany, flew at five times manufactured despite these vehicles exceeding Mach 5. the speed of sound, the first vehicle to be considered hypersonic. Other vehicles to have flown at hypersonicThough speedsthis being are intercontinentalthe case, numerous ballistic experimental missiles, Apollo unmanned space capsules, aircraft the have space attempted shuttle, and and achievedthe experimental hypersonic X-planes speed by [1]. various There has means never of beenpropulsion, a hypersonic makin commercialg hypersonic aircraft flight manufactured of Mach 5 and abovedespite a reality. these vehicles exceeding Mach 5. AirThough-breathing this hypersonic being the case, propulsion numerous can experimentalhelp put aircraft unmanneds into orbit aircraft or sustain have attemptedflight within and the atmosphereachieved hypersonic with lower speed weight by and various propulsion means of required propulsion, compared making to hypersonic rockets, as flight the ofoxidizer Mach 5 (air) and is takenabove from a reality. the environment as opposed to being carried onboard. Hypersonic air-breathing commercialAir-breathing flight will hypersonic potentially propulsion offer great can advancements help put aircrafts in reliability, into orbit reusability or sustain, and flight economies within of thescale atmosphere for high-speed with loweratmospheric weight cruis and propulsioning. These proposed required compared vehicles a tond rockets, methods as theof propulsion oxidizer remove(air) is the taken need from to carry the environment oxidizers and as other opposed limitations to being which carried rocket onboard. engines Hypersonic incur and air-breathing increase the possibilitycommercial of achieving flight will the potentially desired offerrange, great payload advancements, and efficiency in reliability, [2]. reusability, and economies ofSeveral scale for air high-speed-breathing atmospheric propulsion cruising.methods These like turbojet, proposed turbofan, vehicles andramjets methods, and ofscramjets propulsion have beenremove adopted the needin the to past carry to oxidizers utilize high and- otherspeed limitations air-breathing which flight. rocket The engines limitations incur and observed increase within the thepossibility turbojet are of achievingthat the maximum the desired rotational range, payload, speed of and the efficiency rotor and [2 ].the maximum temperature of the gases inSeveral front of air-breathing the turbine a propulsionffect the durability methods of like theturbojet, turbine blades. turbofan, Consequently, ramjets, and engine scramjets reliability have is riskedbeen adopted during inoperation the past and to utilize the flight high-speed speed is air-breathing limited [3]. flight. The limitations observed within theRamjet turbojet and are s thatramjet the engines maximum utilize rotational the “ram speed” effect, of the by rotor exploiting and the maximumthe high speeds temperature and dynamic of the gases in front of the turbine affect the durability of the turbine blades. Consequently, engine reliability air pressure to compress the intake air, and thus, avoid the need for rotational components [4]. In is risked during operation and the flight speed is limited [3]. addition, ramjets can only produce thrust when the vehicle is moving, meaning other propulsion Ramjet and sramjet engines utilize the “ram” effect, by exploiting the high speeds and dynamic air systems are necessary to accelerate the vehicle to a speed where the ramjet becomes operable (Mach pressure to compress the intake air, and thus, avoid the need for rotational components [4]. In addition, 2.5–3) [5–7]. ramjets can only produce thrust when the vehicle is moving, meaning other propulsion systems are The scramjet (supersonic combustion ramjet) is a variant of the ramjet engine and similarly relies necessary to accelerate the vehicle to a speed where the ramjet becomes operable (Mach 2.5–3) [5–7]. on the vehicleThe scramjet’s speed (supersonic to compress combustion the air prior ramjet) to combustion. is a variant of Scramjets the ramjet are engine usually and utilized similarly at relies Mach 5 andon theabove vehicle’s because speed of tothe compress ramjet’sthe inability air prior to toovercome combustion. the Scramjetsdrag at Mach are usually 5 (Figure utilized 1). In at scramjets, Mach 5 theand airfl aboveow remains because supersonic of the ramjet’s as it inabilitypasses through to overcome the engine the drag including at Mach the 5 (Figure combustor1). In, scramjets, whereas in thethe ramjet airflow, flow remains is decelerated supersonic to assub itsonic passes velocity through for the combustion. engine including A scramjet the combustor, operates whereasefficiently in at hypersonicthe ramjet, speeds flow is and decelerated allows tofor subsonic supersonic velocity combustion for combustion. by compressing A scramjet operatesthe incoming efficiently airflow at withouthypersonic decelerating speeds and it bel allowsow Mach for supersonic 1. Although, combustion a number by compressingof research tests the incoming have been airflow performed without on scramjets,decelerating there it belowis still Macha long 1. Although,way to go a for number this oftechnology research tests to be have commercialized been performed [7,8 on]. scramjets, A typical scramjetthere is consists still a long of waya converging to go for this inlet, technology isolator, to combustion be commercialized chamber [7,,8 ].and A typicala divergi scramjetng nozzle. consists The basicof aschematic converging and inlet, the isolator, combustion combustion process chamber, in