Subsonic Flight Regime Research Articles

Utilizing Artificial Neural Networks for Entry Vehicle Aerodynamic Characterization

Determining the dynamic stability of blunt body entry vehicles is a persistent engineering challenge, particularly in the low supersonic to subsonic flight regime where the behavior of the unsteady wake is a primary contributor. Dynamic stability quantities are determined by fitting measurements of a ballistic range campaign or a computational fluid dynamics (CFD) computational experiment to an assumed functional form in order to regress quasi-static stability coefficients. However, this data reduction process has many implicit assumptions that may not hold. This paper explores novel alternatives to the established methods for modeling blunt body aerodynamics. A six-degree-of-freedom CFD-in-the-loop flight model is used to run “virtual ballistic range tests,” fully capturing the relevant flow physics. Feed-forward and time-delay neural network models are fitted to the time-series trajectory and aerodynamic results, which can then be used to predict aerodynamic forces and moments. These models do not have a prescribed functional form and do not assume linearized aerodynamics. The models are evaluated for goodness-of-fit in their aerodynamic and trajectory prediction. The feed-forward neural network model resulted in a better prediction of the virtual ballistic range tests than a traditional database. The time-delay network had good open-loop performance but suffered from closed-loop instability.

Design space optimisation of an unmanned aerial vehicle submerged inlet through the formulation of a data-fusion-based hybrid model

ABSTRACTThe research focuses on the design space optimisation of National Advisory Committee for Aeronautics (NACA) submerged inlets through the formulation of a hybrid data fusion methodology. Submerged inlets have drawn considerable attention owing to their potential for good on-design performance, for example during cruise flight conditions. However, complexities due to the geometrical topology and interactions among various design variables remain a challenge. This research enhances the current design knowledge of submerged inlets through the utilisation of data mining and Computational Fluid Dynamics (CFD) methodologies, focusing on design space optimisation. A two-pronged approach is employed where the first step encompasses a low-fidelity model through data mining and surrogate modelling to predict and optimise the design parameters, while the second step uses the Design of Experiments (DOE) approach based on the CFD results for the candidate design geometry to construct a surrogate model with high fidelity for design refinement. The feasibility of the proposed methodology is demonstrated for the optimisation of the total pressure recovery of a NACA submerged inlet for the subsonic flight regime. The proposed methodology is found to provide good agreement between the surrogate and CFD-based model and reduce the optimisation processing time by half in comparison with conventional (global-based) CFD optimisation approaches.

Overview of green quad bubble business jet aerodynamic configuration design

PurposeThe purpose of this paper is to explore the possibilities of introducing a number of visionary and pioneering ideas and upcoming enabling technologies for a conceptual and aerodynamic design of green business jet aircraft to meet various requirements within Green and N + 2 Aircraft framework, and at the same time, to meet the requirements of air transportation demand, economic growth and environmental conservation.Design/methodology/approachA synthesis of various aircraft design methodologies has been carried out through iterative optimization to arrive at the conceptually designed aircraft with novel concept with optimum performance within the subsonic flight regimes. Major ideas derived from D8 and other novel concepts are appropriately applied in the work, which starts with fuel efficient motivation, and followed by wing aerodynamics and other critical factors related to the design requirements and objectives.FindingsThrough a meticulous effort following the synthesized design methodologies in the conceptual design phase, a conceptual design of a quad-bubble business jets with a set of specifications that meet the green and N + 2 aircraft technology requirements and exhibit promising performances is proposed and assessed within recent aircraft technology development.Research limitations/implicationsThe research work is limited to conceptual design and analytical work which should be followed by further iterative steps incorporating experiments and detailed structural and aerodynamic computations.Practical implicationsThe conceptual design proposed can be utilized as a baseline for further practical step in an aircraft development project.Social implicationsThe conceptual design proposed could be utilized for business and economic study for future air transportation system.Originality/valueThe work is original, incorporating review of state-of-the-art technology, environmental requirements and a synthesis of a novel product.

Aerodynamic optimisation of the rocket plane in subsonic and supersonic flight conditions

This paper presents the results of a numerical study of the aerodynamic shape of the Rocket Plane LEX. The Rocket Plane is a main part of the Modular Airplane System – MAS; a special vehicle devoted to suborbital tourist flights. The Rocket Plane was designed for subsonic and supersonic flight conditions. Therefore, the impact of the Mach number should be considered during the aerodynamic design of the Rocket Plane. The main goal of the investigation was to determine the sensitivity of the Rocket Plane aerodynamic characteristics to the Mach number during the optimisation of the LEX geometry. The paper includes results of the optimisation process for Mach number from the range Ma = 0.5 to Ma = 2.5. These results reveal that the aerodynamic characteristics of models optimised for the subsonic and transonic regime of Mach numbers (up to Ma = 1) were also improved for the supersonic speed regime. However, in the case of models optimised for the supersonic flight regime the aerodynamic characteristics in subsonic flight regime, are inferior compared to the model before the optimisation process.

Aerodynamic Flow Characteristics of Utilizing Delta Wing Configurations in Supersonic and Subsonic Flight Regimes

Computational fluid dynamic tests are performed on delta wing models at different heights and speeds in order to achieve lift and drag coefficient values. Primarily, testing was done at supersonic speeds to reveal the advantages of these wing configurations at supersonic flight regimes at a cruise speed and altitude. The low speed characteristics are also examined, important for take-off and landing regimes where the distinctive vortices become prominent. Throughout the two flight conditions tested, a simple delta wing model (with a straight swept wing) is compared to a delta wing model that exhibited a ‘LERX’ (leading edge root extension). Provided literature describes how the performance of delta wings can be improved through this inclusion. Results obtained from the tests show that the model with the LERX has a small, but significant, performance improvement over the simple delta model, in respect to the maximum achievable lift coefficient and maximum stall angle. Lift to drag ratio is not improved however, due to the large vortices creating pressure drag. Generally, the delta wing models produce relatively small amounts of drag, and slightly less lower lift, when at low angles of attack. This is primarily due to the geometry of the models that have thin leading edges and also low thickness to chord ratios.

Numerical Investigation of Cowl Lip Adjustments for a Rocket-Based Combined-Cycle Inlet in Takeoff Regime

AbstractNumerical integration simulations were performed on a ready-made central strut-based rocket-based combined-cycle (RBCC) engine operating in the ejector mode during the takeoff regime. The effective principles of various cowl lip positions and shapes on the inlet operation and the overall performance of the entire engine were investigated in detail. Under the static condition, reverse cowl lip rotation in a certain range was found to contribute comprehensive improvement to the RBCC inlet and the entire engine. However, the reverse rotation of the cowl lip contributed very little enhancement of the RBCC inlet under the low subsonic flight regime and induced extremely negative impacts in the high subsonic flight regime, especially in terms of a significant increase in the drag of the inlet. Changes to the cowl lip shape provided little improvement to the overall performance of the RBCC engine, merely shifting the location of the leeward area inside the RBCC inlet, as well as the flow separation and eddy, but not relieving or eliminating those phenomena. The results of this study indicate that proper cowl lip rotation offers an efficient variable geometry scheme for a RBCC inlet in the takeoff regime.

Numerical Study of a Boundary Layer Bleedfor a Rocket-Based Combined-Cycle Inlet in Ejector Mode

AbstractFully integrated numerical simulations were performed for a ready-made central strut-based rocket-based combined-cycle (RBCC) engine operating in ejector mode, and the applicability of using a boundary layer bleed in the RBCC inlet designed for supersonic speeds was investigated in detail. The operational mechanism of the boundary layer bleed and its effects on the RBCC inlet and the engine under different off-design conditions in ejector mode were determined. The boundary layer bleed played different roles in the RBCC inlet for different flight regimes. When the RBCC engine took off, some air was entrained into the inlet through the bleed block, thereby inducing significant flow separation and a low-speed vortex, which deteriorated the inner flow and reduced the entraining air mass flow rate: thus, the total pressure loss increased and extra drag was exerted on the inlet. In the low subsonic regime, the bleed block had almost no impact on the RBCC engine and its inlet. However, as the RBCC engine accelerated into a high subsonic flight regime, the boundary layer bleed had a clearly positive effect, comprehensively improving the performance of the RBCC inlet. A boundary layer bleed operation strategy for the RBCC inlet in ejector mode was also developed in this study.

Aeroservoelasticity Analysis Method Based on an Error Analytical Form Applied on a Business Aircraft

Aeroservoelasticity is a multidisciplinary study that combines the following disciplines: aerodynamics, aeroelasticity and servo-controls. For aeroelasticity studies, the Doublet Lattice Method (DLM) is used to calculate the aerodynamic unsteady forces for a set of reduced frequencies k and Mach numbers M on a business aircraft in the subsonic flight regime. There are three classical methods in the aeroservoelasticity used to approximate these forces Q (k, M) by rational functions in the Laplace domain Q(s): Least Square (LS), Matrix Padé (MP) and Minimum State (MS). A new method called Corrected Least Square (CLS) is presented. This new method uses an analytical form of the error as a function of Laplace variable similar to the analytical form of the aerodynamic forces calculated by use of the LS method. The new CLS method does not take additional time to the computation of the unsteady aerodynamic forces when compared to the LS method, and the aerodynamic forces calculated with the CLS method are closer to the aerodynamic forces data in the frequency domain than the aerodynamic forces calculated by the standard LS method. The new CLS method applied on a business aircraft gives better results (flutter speeds and frequencies) and faster (as it uses smaller number of lag terms) than the LS method.

Improved Method for Creating Time-Domain Unsteady Aerodynamic Models

Multidisciplinary aeroservoelastic interactions are studied by the combination of knowledge acquired in two main disciplines: aeroelasticity and servocontrols. In aeroelasticity, the doublet lattice method is used to calculate the unsteady aerodynamic forces for a range of reduced frequencies and Mach numbers on a business aircraft in the subsonic flight regime by use of NASTRAN software. For aeroservoelasticity studies, there is the need to conceive methods for these unsteady aerodynamic forces conversions from frequency into Laplace domain. A new method different from classical methods is presented, in which Chebyshev polynomials theories and their orthogonality properties are applied. In this paper, a comparison between flutter results expressed in terms of flutter speeds and frequencies obtained with our method with flutter results obtained with classical Pade and least squares methods is presented for a business aircraft at one Mach number and a range of reduced frequencies. It has been found that results obtained with our method are better in terms of average error than results obtained with the two classical methods here presented.

Physical modelling of a flight control system

AbstractThis paper deals with the methods of physical modelling of Flight Control Systems (FCS) by means of Dynamically Similar free-flying Models (DSM) for the investigation of stability and controllability of aircraft at subsonic flight speeds. The subsonic flight regime allows us to avoid Mach number similarity considerations. The large scale of the DSM meets autosimilarity of Reynolds numbers, whilst Froude similarity is assured during the development and manufacturing of the DSM. This paper proves the presence of necessary and sufficient conditions of similarity for the FCS of an aircraft, and that of its DSM. The existence of necessary conditions have been proved both mathematically (by means of the π – Theorem from the theory of dimensions), and with equations involving physical quantities. The generalised scale coefficients for transitioning from the FCS’s aircraft gain factors, to those of the FCS of the DSM have been obtained, and it is shown that the coefficients depend only on the linear scale of the DSM.

The conceptual design of deck-launched waverider-configured aircraft

The results of five graduate classroom design teams are reviewed in order to assess the feasibility of carriercapable tactical waverider-configured aircraft designed for cruise Mach numbers in the range 3≤M∞≤5. The efforts of the design teams suggests that such aircraft are probably feasible for combat radii of 580nm<R<1500nm. Low-speed research to support the development of such aircraft indicates that within the subsonic flight regime, waverider planforms may be statically unstable, vortex lift may be less strong for waverider configurations than for similar simple delta wing planforms and lift, drag and pitching moment data appear to be well behaved within a large (−20°≤α≤20° data shown herein) angle-of-attack range.

Numerical Simulation of the Interaction Between Leading-Edge Vortex and Vertical Tail

The impingement of a streamwise vortex on an aerodynamic surface, such as a fin or tail, can result in efficiency loss, severe unsteady loading, vibration, and adverse stability and control. Such vortices, commonly generated by modern fighter aircraft configurations, are employed to supplement lift and enhance performance and maneuvering capabilities in the high-angle-of-attack subsonic flight regime. In these flow situations, vortex breakdown can occur, leading to buffet of the tail surface with a potential for fatigue induced structural failure. The present investigation considers airflow at a freestream Mach number of 0.2 and root chord Reynolds number of 1.89 X 10 6 past a sharp leading-edge 70.0-deg swept delta wing at an angle of attack of 23.2 deg.