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Random Data Analysis And Measurement Procedures

H YPERSONIC flight began in February 1949 when a WAC Corporal rocket was ignited from a U.S.-captured V-2 rocket [1]. In the six decades since this milestone, there have been significant investments in the development of hypersonic vehicle technologies. The NASA X-15 rocket plane in the early 1960s represents early research toward this goal [2,3]. After a lull in activity, the modern era of hypersonic research started in the mid-1980s with the National Aerospace Plane (NASP) program [4], aimed at developing a single-stage-to-orbit reusable launch vehicle (RLV) that used conventional runways. However, it was canceled due mainly to design requirements that exceeded the state of the art [1,5]. A more recent RLV project, the VentureStar program, failed during structural tests, again for lack of the required technology [5]. Despite these unsuccessful programs, the continued need for a low-cost RLV, as well as the desire of the U.S. Air Force (USAF) for unmanned hypersonic vehicles, has reinvigorated hypersonic flight research. An emergence of recent and current research programs [6] demonstrate this renewed interest. Consider, for example, the NASA Hyper-X experimental vehicle program [7], the University of Queensland HyShot program [8], the NASA Fundamental Aeronautics Hypersonics Project [9], the joint U.S. Defense Advanced Research Projects Administration (DARPA)/USAF Force Application andLaunch fromContinentalUnited States (FALCON) program [10], the X-51 Single Engine Demonstrator [11,12], the joint USAF Research Laboratory (AFRL)/Australian Defence Science and Technology Organisation Hypersonic International Flight Research Experimentation project [13], and ongoing basic hypersonic research at the AFRL (e.g., [14–20]). The conditions encountered in hypersonic flows, combined with the need to design hypersonic vehicles, have motivated research in the areas of hypersonic aeroelasticity and aerothermoelasticity. It is evident from Fig. 1 that hypersonic vehicle configurations will consist of long, slender lifting body designs. In general, the body, surface panels, and aerodynamic control surfaces are flexible due to minimum-weight restrictions. Furthermore, as shown in Fig. 2, these

/pdf/aeroelastic-and-aerothermoelastic-analysis-in-hypersonic-4ycxg0c3dg.pdf

Aeroelastic and Aerothermoelastic Analysis in Hypersonic Flow: Past, Present, and Future

Effects of chordwise, spanwise, and isotropic flexibility on the force generation and propulsive efficiency of flapping wings are elucidated. For a moving body immersed in viscous fluid, different types of forces, as a function of the Reynolds number, reduced frequency (k), and Strouhal number (St), acting on the moving body are identified based on a scaling argument. In particular, at the Reynolds number regime of O(10 3 - 10 4 ) and the reduced frequency of O(1), the added mass force, related to the acceleration of the wing, is important. Based on the order of magnitude and energy balance arguments, a relationship between the propulsive force and the maximum relative wing tip deformation parameter (γ) is established. The parameter depends on the density ratio, St, k, natural and flapping frequency ratio, and flapping amplitude. The lift generation, and the propulsive efficiency can be deduced by the same scaling procedures. It seems that the maximum propulsive force is obtained when flapping near the resonance, whereas the optimal propulsive efficiency is reached when flapping at about half of the natural frequency; both are supported by the reported studies. The established scaling relationships can offer direct guidance for MAV design and performance analysis.

/pdf/effects-of-flexibility-on-the-aerodynamic-performance-of-5gmapnl1kx.pdf

Effects of Flexibility on the Aerodynamic Performance of Flapping Wings

Applications of the unsteady vortex-lattice method in aircraft aeroelasticity and flight dynamics

AEROSPACE LETTERS are brief communications (approximately 2000 words) that describe new and potentially important ideas or results, including critical analytical or experimental observations that justify rapid publication They are stringently prescreened, and only a few are selected for rapid review by an Editor They are published as soon as possible electronically and then appear in the print version of the journal

/pdf/flapping-wings-and-aerodynamic-lift-the-role-of-leading-edge-2huzbb6274.pdf

Flapping Wings and Aerodynamic Lift: The Role of Leading-Edge Vortices

DOI: 10.2514/1.C000190 Various approximations to unsteady aerodynamics are examined for the aeroelastic analysis of a thin doublewedge airfoil in hypersonic flow. Flutter boundaries are obtained using classical hypersonic unsteady aerodynamic theories: piston theory, Van Dyke’s second-order theory, Newtonian impact theory, and unsteady shock-expansion theory. The theories are evaluated by comparing the flutter boundaries with those predicted using computational fluid dynamics solutions to the unsteady Navier–Stokes equations. Inaddition, several alternative approaches to the classical approximations are also evaluated: two different viscous approximations based on effective shapes and combined approximate computational approaches that use steady-state computational-fluid-dynamics-based surrogatemodelsinconjunction withpistontheory.Theresultsindicatethat,with theexceptionof first-order piston theory and Newtonian impact theory, the approximate theories yield predictions between 3 and 17% of normalized root-mean-square error and between 7 and 40% of normalized maximum error of the unsteady Navier–Stokes predictions. Furthermore, the demonstrated accuracy of the combined steady-state computational fluid dynamics and piston theory approaches suggest that important nonlinearities in hypersonic flow are primarily due to steadystate effects. This implies that steady-state flow analysis may be an alternative to time-accurate Navier–Stokes solutions for capturing complex flow effects.

/pdf/approximate-modeling-of-unsteady-aerodynamics-for-hypersonic-4s2zdi7crr.pdf

Approximate Modeling of Unsteady Aerodynamics for Hypersonic Aeroelasticity

Response of a panel to shock impingement: Modeling and comparison with experiments - part 2

Shock wave/boundary-layer interactions represent an extreme loading condition in the structural design of high-speed flight vehicles. However, the complexity of this problem has primarily restricte...

Interplay of Surface Deformation and Shock-Induced Separation in Shock/Boundary-Layer Interactions

A nonlinear aeroelastic model suitable for flexible insectlike flapping wings in hover is presented. The aeroelastic model is obtained by coupling a nonlinear structural dynamic model based on MARC, with a potential-flow-based approximate aerodynamic model that consists of leading-edge vortices and a wake model. The aeroelastic response is obtained using an updated Lagrangian method. The paper describes validation studies conducted on the structural dynamic model, aerodynamic comparisons, and aeroelastic studies conducted on isotropic and anisotropic Zimmerman wings. The results demonstrate the suitability of MARC for modeling anisotropic wings undergoing insectlike wing kinematics. For the aeroelastic cases considered, the approximate model shows acceptable agreement with computational-fluid-dynamics-based and experimental results. The approximate model captured several important trends correctly.

Abhijit Gogulapati

Papers

Approximate Modeling of Unsteady Aerodynamics for Hypersonic Aeroelasticity

Response of a panel to shock impingement: Modeling and comparison with experiments - part 2

Interplay of Surface Deformation and Shock-Induced Separation in Shock/Boundary-Layer Interactions

Approximate Aeroelastic Modeling of Flapping Wings in Hover

Approximate Aeroelastic Model of Flapping Wings in Hover