Supersonic Transport Research Articles

Modified Target Pressure Distribution for Supersonic Natural Laminar Flow Wing Design

Natural laminar flow (NLF) is an important technique for reducing drag of the next-generation supersonic transport aircraft. However, achieving NLF on supersonic transport wings is challenging due to the large swept angles and high-Reynolds-number conditions, which significantly amplify Tollmien–Schlichting (TS) and crossflow (CF) instabilities. To address this problem, this paper proposes a modified target pressure distribution to attenuate the TS and CF instabilities. Compared with conventional targets defined using empirical functions, it is derived in two steps: the first step is to prescribe an initial flat target pressure distribution with a narrow leading-edge flow acceleration region and conduct inverse designs; the second step is to modify the target pressure distribution according to the stability analysis results of the designed wing in order to achieve a balance of disturbance growth at positive and negative wave angles. The proposed approach is validated on a 60°-swept infinite-span wing at Ma=2 and Re=1.39×107. Results demonstrate that TS and CF instabilities are well-suppressed under the modified target pressure distribution, with the transition location delayed from xtr/c=0.26 on the baseline wing to xtr/c=0.95 on the designed wing, suggesting that the proposed method is effective for NLF design on supersonic highly swept wings.

PLR and take-off speed implications on noise contours and local gaseous emissions for SST business jet concept aircraft

DLR has established a simulation process to evaluate the landing and take-off of novel civil supersonic transport (SST) aircraft. This process was applied to two business jet concept aircraft in order to assess the certification noise levels according to novel regulations under discussion at ICAO CAEP. It has to be noted, that neither of the concept aircraft is optimized for low noise nor for low boom. At DLR, modifications to departure flight procedures are under investigation, i.e., an automated thrust reduction referred to as Programmed Lapse Rate and an increased take-off speed. These measures as proposed by NASA promise to reduce the certification noise levels for the two departure locations. For the two considered concept aircraft, promising procedures with reduced noise at the certification locations have been identified previously. This paper now addresses the impact of these promising departure procedures on noise contour areas and local gaseous emissions. Impact on EPNL and SEL contours and differences in CO2 and NOX are assessed along the simulated flights. It is demonstrated, that the proposed procedures do not only reduce noise at the certification locations but also noise contour areas and gaseous pollutants.

Sensitivity analysis of landing and takeoff noise for conceptual low-boom supersonic aircraft using variable noise reduction system

This paper presents the results of an analysis of the sensitivity of the use of a variable noise reduction system (VNRS), considered in the new landing and takeoff (LTO) noise standard for supersonic aircraft, using a Japan Aerospace Exploration Agency (JAXA)-designed 66-ton twin-engine conceptual low-boom supersonic airliner as an example. The analysis was conducted using a tool developed by JAXA and examined the sensitivity of low-speed aerodynamic performance, the sensitivity of takeoff reference speed, the sensitivity of thrust control and flap control duration time ranges, and the sensitivity of noise level to takeoff profile uncertainty. The analyses showed that improving low-speed aerodynamic performance and increasing the takeoff reference speed significantly impact noise levels and the use of VNRS could reduce noise by 2.1 EPNLdB while maintaining the performance of the aircraft. Because the effective noise reduction method by changing the takeoff procedure considered differs for each noise measurement point, it is important to design a takeoff procedure that incorporates an appropriate VNRS. Uncertainty of the takeoff profile was also investigated using Monte Carlo simulations, and it was shown that noise reduction by VNRS is effective even with the assumed uncertainty in the takeoff profile.

Development of means for suppressing the negative effects of interaction between the pilot and reentry and other high-speed vehicles

Several novel active and passive means for the suppression of pilot-induced oscillations are considered in the paper. The potential of the proposed means in eliminating Category I, II, and III pilot-induced oscillations was studied in ground-based simulation for two controlled element dynamics corresponding to an aerospace vehicle and a second-generation supersonic transport. The experiments demonstrated that the highest effectiveness in suppressing pilot-induced oscillations and improving task performance is provided by integrating both proposed active suppressors with one of the passive prefilters.

Integrated Model for Predicting Demand of Supersonic Transports Under Low-Boom Constraint

Commercial supersonic aircraft could return between 2035 and 2040 due to the desire for fast travel and advancements in technology that could reduce the cost of supersonic transport. Nevertheless, several challenges remain to make supersonic travel a reality. This paper presents an integrated model that ties the aircraft preliminary design process, the economics of aircraft development and operations, and passenger preferences to estimate worldwide demand for subsonic overland, Mach cutoff, and low-boom aircraft design concepts. This comprehensive and iterative methodology takes into account the uncertainty of market demand for supersonic travel and the complexities of supersonic network operations. Based on the study of four conceptual supersonic designs, we found that low-boom aircraft could attract 28% more demand worldwide compared to an optimized Mach cutoff design because of the additional time-saving benefits on overland routes. The results of this work offer valuable guidance to aircraft designers by explicitly tying the technical parameters of a design and the potential market demand. In addition, the integrated model developed may streamline the initial design development cycle by quantifying fleet size as part of an integrated modeling process.

Attenuation of boundary-layer instabilities for natural laminar flow design on supersonic highly swept wings

To meet the challenge of drag reduction for next-generation supersonic transport aircraft, increasing attention has been focused on Natural Laminar Flow (NLF) technology. However, the highly swept wings and high-Reynolds-number conditions of such aircraft dramatically amplify Crossflow (CF) instabilities inside boundary layers, making it difficult to maintain a large laminar flow region. To explore novel NLF designs on supersonic wings, this article investigates the mechanisms underlying the attenuation of Tollmien–Schlichting (TS) and CF instabilities by modifying pressure distributions. The evolution of TS and CF instabilities are evaluated under typical pressure distributions with different leading-edge flow acceleration region lengths, pressure coefficient slopes and pressure coefficient deviations. The results show that shortening the leading-edge flow acceleration region and using a flat pressure distribution are favorable for suppressing CF instabilities, and keeping a balance of disturbance growth between positive and negative wave angles is favorable for attenuating TS instabilities. Based on the uncovered mechanisms, a strategy of supersonic NLF design is proposed. Examination of the proposed strategy at a 60° sweep angle and Ma = 2 presents potential to exceed the conventional NLF limit and achieve a transition Reynolds number of 17.6 million, which can provide guidance for NLF design on supersonic highly swept wings.

Jet noise of a low bypass turbofan with internal mixing and external plug

Jet noise generated by turbofan engines which are designed for supersonic aircraft operation is expected to remain a challenge for the aerospace industry. For civil supersonic transport, low bypass ratio engines with internal mixing and external plugs are currently seen as promising exhaust architecture to meet aircraft mission and certification requirements. Measurements of the noise from a representative low-bypass ratio long duct mixed flow with external plug exhaust configuration were made, along with corresponding steady-RANS and LES analyses. The measured data showed excess high frequency noise across a wide range of operating conditions as compared to an equivalent single stream jet, or an equivalent uniform jet with internal plug. The absolute levels of the excess noise were relatively insensitive to forward flight, and the excess noise was most dominant when the primary and secondary streams had large velocity and temperature mismatch just upstream of the internal mixer. Preliminary indications from the LES analysis also indicated that significant pressure fluctuations, at the same frequencies which are insensitive to forward flight, develop inside the nozzle as the internal shear layer from the mixer grows and gets accelerated by the external plug. Parametric study test measurements on the fan and core operating conditions were performed, providing support for the hypothesis that the excess noise is generated as the internal shear layer, starting inside the nozzle, gets accelerated by the plug and passes through the weak shock at the nozzle exit where the flow accelerates more and turns over the external plug.

When discrete fronts and pulses form a single family: FPU chain with hardening-softening springs

We consider a version of the classical Hamiltonian FPU (Fermi–Pasta–Ulam) problem with nonlinear force-strain relation in which a hardening response is taken over by a softening regime above a critical strain value. We show that in addition to pulses (solitary waves) this discrete system also supports non-topological and dissipation-free fronts (kinks). Moreover, we demonstrate that these two types of supersonic traveling wave solutions belong to the same family. Within this family, solitary waves exist for continuous ranges of velocity that extend up to a limiting speed corresponding to kinks. As the kink velocity limit is approached from above or below, the solitary waves become progressively more broad and acquire the structure of a kink–antikink bundle. Direct numerical simulations and Floquet analysis of linear stability suggest that all of the obtained solutions are effectively stable. To motivate and support our study of the discrete problem we also analyze a quasicontinuum approximation with temporal dispersion. We show that this model captures the main effects observed in the discrete problem both qualitatively and quantitatively.

Optimal control model as an approach to the synthesis of a supersonic transport control system

Optimal control model as an approach to the synthesis of a supersonic transport control system

Reduced-Order Model for Supersonic Transport Takeoff Noise Scaling with Cruise Mach Number

The recent interest in the development of supersonic transport raises concerns about an increase in community noise around airports. As noise certification standards for supersonic transport other than Concorde have not yet been developed by the International Civil Aviation Organization, there is a need for a physics-based scaling rule for supersonic transport takeoff noise performance. Assuming supersonic transport takeoff noise levels are dominated by the engine mixed jet velocity and the aircraft-to-microphone propagation distance, this paper presents a reduced-order model for supersonic transport takeoff noise levels as a function of four scaling groups: cruise Mach number, takeoff aerodynamic efficiency, takeoff speed, and number of installed engines. This paper finds that, as cruise Mach number increases, supersonic transport takeoff noise levels increase while their thrust cutback noise reduction potential decreases. Assuming constant aerodynamic efficiency, takeoff speed, and number of installed engines, the takeoff noise levels and noise reduction potential of a Mach 2.2 aircraft are found to be ∼15.3 dB higher and ∼19.2 dB less compared to a Mach 1.4 aircraft, respectively. This scaling rule can potentially yield a simple guideline for estimating an approximate noise limit for supersonic transport, depending on their cruise Mach number.

Profitability of supersonic travel

Since the retirement of the Concorde in 2003 no commercial supersonic flights were operated. In 2014 the aircraft manufacturing start-up Boom announced the development of a supersonic aircraft by 2029 and has since gathered 130 orders. This paper analyzes the profitability of this aircraft by calculating the net present value of an investment decision and comparing this to a subsonic aircraft. It is determined that supersonic travel has 50% higher cash operating costs per seat. This implies that, for example, a return flight LHR-JFK merely breaks even at a WACC of 6%. The central question of this paper is whether this cost premium can be covered by a price premium paid for the time saved on a supersonic flight. A schedule analysis shows that this price premium is justified on westbound but not on eastbound flights. Thus, a westward rotation of the supersonic fleet is proposed. To avoid seat imbalances this network can be supplemented by an eastward rotating subsonic narrowbody fleet in an all-business configuration. Whereas a supersonic rotation A - B - A only breaks even with a net present value close to zero, a westward supersonic rotation A - B - C - A complemented by a subsonic rotation A - C - B - A achieves a significant profit reflected in a net present value of over $ 40 mill. per aircraft. It follows that this network structure is the only profitable one.As a by-product it is reconstructed that the Concorde was marginally cash-positive, explaining why operations was kept up for 27 years but no aircraft were ordered after the initial batch.

Supersonic passenger aircraft, the Oedipus Trap and the reluctance to reverse a decision.

Supersonic passenger aircraft, the Oedipus Trap and the reluctance to reverse a decision.

Optimization of the Aerodynamic Configuration of the Isolated Wing for the Second-Generation Supersonic Passenger Aircraft

Optimization of the Aerodynamic Configuration of the Isolated Wing for the Second-Generation Supersonic Passenger Aircraft

A Review of the Current Regulatory Framework for Supersonic Civil Aircraft: Noise and Emissions Regulations

The request for faster and greener civil aviation is urging the worldwide scientific community and aerospace industry to develop a new generation of supersonic aircraft, which are expected to be environmentally sustainable, and to guarantee a high level of protection for citizens. The availability of novel propulsive technologies, together with the development of new civil supersonic passenger aircraft configurations and missions, is pushing international authorities to update the regulatory framework to limit nuisances on the ground and the contribution to climate change. Existing ICAO noise and emissions standards are outdated as they were developed in the 1970s and tailored to Concorde, the only SST that has ever operated in Western airspace. This article provides (i) a comprehensive review of current environmental regulations for SST, encompassing noise and pollutant emissions near airports (LTO cycle) as well as CO2 emissions and sonic booms, and (ii) updated information about the ongoing rulemaking activities by ICAO, FAA and EASA. This review clearly highlights the following findings: (i) the need to revise current rules to better fit future SST design, operations and technologies; (ii) the need to introduce new regulations to cover additional aspects, including stratospheric water vapour emissions and ozone depletion; and (iii) the need to support regulatory activities with solid technical bases, fostering cooperation with academia, research centres and industry in R&D projects. Eventually, a practical example of how SST rulemaking activities are supported by the collaborative research H2020 MORE&LESS is reported.

Predicting Take-Off Noise, Sonic Boom, and Landing Noise of Supersonic Transport Aircraft Concepts

In 2023, the German Aerospace Center (DLR) has launched the STORMIE (Supersonic Transport Open Research Models and Impact on Environment) project. Focus of the project is the prediction and minimization of environmental and human impacts of civil supersonic transport. Data generated in the project will be used to inform national and European authorities in order to discuss certification standards for supersonic aircraft within the International Civil Aviation Organization's Committee on Aviation Environmental Protection (CAEP). In order to assess the environmental impacts, representative civil supersonic business-jet and airliner concepts will be designed. This paper will present an overview of past and ongoing activities conducted at DLR to assess and minimize landing and take-off noise as well as the sonic boom of supersonic aircraft. Numerical methods at different levels of fidelity are applied and will be complemented by listening tests of auralized simulation data in a later project stage. First noise-related activities within the STORMIE project are summarized.

On ecologically-safe high-speed vehicles: Conceptual design study of the next generation supersonic transport

Space-age technology makes it possible to travel faster than the speed of sound from one continent to another one or even to make suborbital flight as a space tourism. The existing technology challenge is to bring this innovative way of travel without damaging the environment to ensure human safety and to preserve environment balance. The sonic boom issue is one of the concerns when flying faster than sound. The issue must be taking into account at the stage of developing environmentally friendly high-speed vehicle. The next generation supersonic transport is fundamentally different from subsonic medium- and long-range aircraft in a breakthrough feature: it ensures a long-term supersonic cruise flight in the range of Mach numbers 1.6–1.8. For a successful implementation of the civil supersonic project at a new stage of technology development, it is necessary to solve a number of scientific and technical problems. In the present paper some of them are under discussion. In particular, the addressed issues are as follows: how to achieve a high level of aerodynamic efficiency at supersonic cruise along with low sonic boom; how to fit into low noise requirements at take-off and landing modes of supersonic aircraft with a moderate-bypass-ratio engine; how to implement a wing with high load factor and fuselage with long nose part to fit into required airframe structural stiffness, etc. Also, new technology approaches in multidisciplinary optimization task to achieve aircraft design goals of low drag, low boom and low noise characteristics are discussed. A few examples of optimal supersonic aircraft configurations along with passenger cabin are given. The paper was presented at the X-th IAA Symposium “Space Flight Safety” in St.-Petersburg on June 2023.

Automatic Continuous Thrust Control for Supersonic Transport Takeoff Noise Reduction

Advanced takeoff trajectories are proposed for supersonic transport noise reduction by capitalizing on excess engine thrust and improved aerodynamic efficiency at higher takeoff speeds. These novel trajectories use i) automatic continuous control of thrust, ii) increased takeoff speed, and iii) reduced cut-back altitude, compared to conventional pilot-initiated discrete thrust cut-back procedures currently used for subsonic transport. In this paper, we develop an optimal control framework to assess the attributes of effective takeoff trajectories for supersonic transport that yield minimum noise levels. We quantify the noise reduction potential of advanced takeoff trajectories for the eight-passenger, 55-metric-ton, Mach-1.4 NASA Supersonic Technology Concept Airplane. For the aircraft examined, these advanced takeoff trajectories enable a cumulative certification noise reduction of 10.6 EPNdB, which is insufficient to meet current subsonic transport noise limits.

Robust Constrained Multi-Objective Guidance of Supersonic Transport Landing Using Evolutionary Algorithm and Polynomial Chaos

Landing of supersonic transport (SST) suffers from a large uncertainty due to its highly sensitive aerodynamic properties in the subsonic domain, as well as the wind gusts around runways. At the vehicle design stage, a landing trajectory optimization under wind uncertainty in a multi-objective solution space is desired to explore the possible trade-off in its key flight performance metrics. The proposed algorithm solves this robust constrained multi-objective optimal control problem by integrating non-intrusive polynomial chaos expansion into a constrained evolutionary algorithm. The computationally tractable optimization is made possible through the conversion of a probabilistic problem into an equivalent deterministic representation while maintaining a form of the multi-objective problem. The generated guidance trajectories achieve a significant reduction of the uncertainty in their terminal states with a marginal modification in the control history of the deterministic solutions, validating the importance of the consideration of robustness in trajectory optimization.

Robust sonic boom reduction in primary boom carpet

Japan Aerospace Exploration Agency has conducted a low-boom design for a small-sized (about 50 PAX) supersonic airliner. In this study, sonic boom loudness is evaluated in a primary boom carpet, while the focus boom is not considered. Two geometries having different robustness with respect to loudness distribution in a primary boom carpet are designed. One is designed considering only a cruise Mach number, and sonic boom loudness is reduced at both under-track and off-track positions. The other is designed considering bothcruise and off-design Mach numbers, and the maximum sonic boom loudness in a primary boom carpet is minimized. In the presentation, design examples to achieve low-boom characteristics at both under-track and off-track positions are reported. In addition, a low-boom design concept using canard is proposed to minimize the maximum sonic boom loudness in a primary boom carpet. Finally, differences of loudness distribution in a primary boom carpet between two geometries are discussed.

Characteristics of Vortices around Forward Swept Wing at Low Speeds/High Angles of Attack

The forward-swept wing (FSW), one of the wing planforms used in aircraft, is known for its high performance in reducing wave drag. Additionally, a study has shown that this wing planform can mitigate sonic booms, which pose a significant challenge to achieving supersonic transport (SST). Therefore, FSW is expected to find applications in future SST aircraft owing to aerodynamic advantages at high speeds. However, there is a lack of sufficient knowledge and systematization to improve aerodynamic performance at low speeds and high angles of attack during takeoff and landing. These are crucial for practical implementation. Although the aerodynamic benefits of an FSW in high-speed flight can be harnessed using advanced structural and control technologies, the realization of SST using an FSW is challenging without enhanced research on low-speed aerodynamics. This study explores the practical aerodynamic knowledge of FSWs. We utilized a numerical simulation based on the Navier–Stokes equation and focused on investigating wake vortex phenomena. Our simulation included various wing planforms, including backward-swept wings (BSWs). The results revealed the presence of vortices with lateral axes emanating from the FSW, while longitudinal vortices were observed in the BSW. Based on these results, we developed a theoretical hypothesis for the vortex structure around an FSW.