are described for cMculating unsteady flows over rapidly pitching airfoils. The first method is b... more are described for cMculating unsteady flows over rapidly pitching airfoils. The first method is based on an interactive scheme in which the inviscid flow is ob-
This book is intended primarily as a textbook for second-year undergraduate students in mathemati... more This book is intended primarily as a textbook for second-year undergraduate students in mathematics, mathematical physics, and engineering. The book is designed as a first introduction to the use of mathematical techniques, within continuum theories. It is presumed that the readers have some knowledge of several variable calculus and partial derivatives. The author presents many physical problems to motivate the discussion of the conservation and balance laws derived in the text; however, the emphasis of the book is on the solution to the resulting ordinary and partial differential equations. The physical and practical aspects are used to aid in the formulation of the models and in interpreting the mathematical predictions. To this extent many simple examples that allow closed form solutions are included in the text, which help provide insight into the mathematical solutions presented. Each chapter also includes student exercises with solutions given in the end of the book. A sizeable number of figures are also included that illustrate details of the mathematical solutions. Chapter 1 begins with a general discussion of conservation and balance laws along with their application to steady state heat flow. Chapter 2 introduces unsteady heat flow and Chapter 3 presents the concepts of fields and potentials with applications in electrostatics. Solutions to Laplace's Equation and Poisson's Equation are presented in Chapter 4. Chapter 5 introduces wave theory in the context of elastic strings. Chapters 6 and 7 give a basic introduction into fluid flow and elasticity, respectively, and provide further context for the mathematical formulations that were derived in previous chapters. Chapter 8 gives a more extensive treatment of plane waves. Wave refraction and reflection and guided waves with applications in acoustics and elasticity are also considered. Chapter 9 extends the topics of Chapter 8 to electromagnetic waves. Finally, the text ends with a presen
This paper presents an overview of the two types of flapping-wing micro air vehicles that have be... more This paper presents an overview of the two types of flapping-wing micro air vehicles that have been developed in recent years. Biomimetic designs imitate nature while biomorphic designs are merely inspired by nature, but incorporate other design features not found in nature. A recent successful biomimetic flapping-wing micro air vehicle-the Microbat, developed by the Aero-Vironment Company-is described. Also, the major design features of a biomorphic micro air vehicle, developed by the authors, are presented in some detail. This design incorporates a fixed wing and two flapping wings arranged very close behind the trailing edge of the fixed wing.
This paper describes experiments that elucidate the dynamic stall phenomenon and the generation o... more This paper describes experiments that elucidate the dynamic stall phenomenon and the generation of thrust by flapping airfoils. To this end, flow visualizations of the vortices shed from a rapidly pitching airfoil and from an oscillating airfoil are presented. Also, wind tunnel tests of two flapping wing models are discussed and thrust measurements on these two models are included.
Modern Ship Engineering, Design and Operations, 2021
High-performance sails, such as the ones used on the America Cup boats, require sails whose aerod... more High-performance sails, such as the ones used on the America Cup boats, require sails whose aerodynamic characteristics approach those of rigid wings, yet permit a reduction in sail area in high wind and sea conditions. To this end, two-cloth sails are coming into use. These sails are constructed out of an articulated forebody that is a truncated ellipse, the aft of which has sail tracks, or rollers, along the edges to accommodate the twin sails. As the sails on either side need to be of the same length, due to the requirement to sail on different tacks, the two cloth sections need to be of equal length. The requirement then is to have their clews separated and able to slide over each other. More importantly, the transition between the rigid mast section and sails needs to be as aerodynamically smooth as possible in order to reduce drag and hence maximize the lift to drag ratio of the airfoil section that is made up of the mast and twin sails. A computational analysis using ANSYS CF...
in Fluid Structure Interaction II, Eds. Chakrabarti, S.K., Brebbia, C.A., Almorza, D. and Gonzale... more in Fluid Structure Interaction II, Eds. Chakrabarti, S.K., Brebbia, C.A., Almorza, D. and Gonzalez-Palma, R., WIT Press, Southampton, UK, 2003, pp. 73-82.
free stream Mach number non-dimensional breakdown rate parameter spot generation rate turbulence ... more free stream Mach number non-dimensional breakdown rate parameter spot generation rate turbulence production term free-stream turbulence at z t C7o] Reynolds number CU/r/ turbulent Reynolds number, k 2 /i/E nondimensional time, la./c Local free-stream velocity free stream velocity magnitude velocity components coordinate parallel to chord transition onset location velocity component of blade surface velocity component of blade surface nondimensional normal wall distance spot spreading half angle, angle of attack intermittency factor ratio of specific heats pressure gradient parameter, (02 /v)/(dU/dr) pressure gradient parameter at r, viscosity kinematic viscosity turbulent viscosity boundary layer momentum thickness density free stream density spot propagation parameter constant of turbulence model differentiation with respect to t quantity on the surface of the blade
Cross-flow fan propulsion has not been seriously considered for aircraft use since an Vought Syst... more Cross-flow fan propulsion has not been seriously considered for aircraft use since an Vought Systems Division (VSD) study for the U.S. Navy in 1975. A recent conceptual design study of lightweight , single seat VTOL aircraft suggest that rotary-engine powered cross-flow fans may constitute a promising alternative to the conventional lift-fan vertical thrust augmentation systems for VTOL aircraft. The cross-flow fan performance data obtained by VSD supported the hypothesis that they could be improved to the point where their thrust augmentation could be used in a VTOL aircraft. In this paper we report results of a NASA Glenn supported experimental and computational cross-flow fan investigation which is currently in progress and we provide an assessment of the potential suitability of crossflow fans for VTOL aircraft propulsion. The tests are carried out in the Turbopropulsion Laboratory of the Naval Postgraduate School, using an existing Turbine Test Rig as a power source to drive the crossflow fan. A 0.305 m (12-inch) diameter, 38.1 mm (1.5-inch) span cross-flow fan test article was constructed to duplicate as closely as possible the VSD fan so that baseline comparison performance data could be obtained. Performance measurements were taken over a speed range of 1,000 to 7,000 RPM and results comparable to those measured by Vought Systems Division were obtained. At 3,000 RPM a 2:1 thrust-to-power ratio was measured which dropped to one as the speed was increased to 6,000 RPM. Performance maps were experimentally determined for the baseline configuration as well as one with both cavities blanked off, for the speed range from 2,000 to 6,000 rpm. Using Flo++, a commercial PC-based computational fluid dynamics software package by Softflo, 2-D numerical simulations of the flow through the cross-flow fan were also obtained. Based on the performance measurements it was concluded that the optimum speed range for this rotor configuration was in the 3,000 to 5,000 rpm range. The lower speed producing the best thrust-to-power ratio and the upper speed range producing the highest efficiency over sizeable throttling range.
A modern energy system based on renewable energy like wind and solar power inevitably needs a sto... more A modern energy system based on renewable energy like wind and solar power inevitably needs a storage system to provide energy on demand. Hydrogen is a promising candidate for this task. For the reconversion of the valuable fuel hydrogen to electricity a power plant of highest efficiency is needed. In this work the Graz Cycle, a zero-emission power plant based on the oxy-fuel technology, is proposed for this role. The Graz Cycle originally burns fossil fuels with pure oxygen and offers efficiencies up to 65% due to the recompression of about half of the working fluid. The Graz Cycle is now adapted for hydrogen combustion with pure oxygen so that a working fluid of nearly pure steam is available. The changes in the thermodynamic layout are presented and discussed. The results show that the cycle is able to reach a net cycle efficiency based on LHV of 68.43% if the oxygen is supplied "freely" from hydrogen generation by electrolysis. An additional parameter study shows the potential of the cycle for further improvements. The high efficiency of the Graz Cycle is also achieved by a close interaction of the components which makes part load operation more difficult. So in the second part of the paper strategies for part load operation are presented and investigated. The thermodynamic analysis predicts part load down to 30% of the base load at remarkably high efficiencies.
Analysis of Low-Speed Unsteady Airfoil Flows, 2005
The differential equations of fluid flow are based on the principles of conservation of mass, mom... more The differential equations of fluid flow are based on the principles of conservation of mass, momentum and energy and are known as the Navier-Stokes equations. For incompressible flows and for flows in which the temperature differences between the surface and freestream are small, the fluid properties such as density ϱ and dynamic viscosity μ in the conservation equations are not affected by temperature. This assumption allows us to ignore the conservation equation for energy and concentrate only on the conservation equations for mass and momentum.
Numerical investigation of subsonic flow over a typical missile forebody
34th Aerospace Sciences Meeting and Exhibit, 1996
Page 1. NUMERICAL INVESTIGATION OF SUBSONIC FLOW OVER A TYPICAL MISSILE FOREBODY Ismail H. Tuncer... more Page 1. NUMERICAL INVESTIGATION OF SUBSONIC FLOW OVER A TYPICAL MISSILE FOREBODY Ismail H. Tuncer, Ron Marviny and Max F. Platzerz Department of Aeronautics and Astronautics Naval Postgraduate School Monterey, California 93943 ABSTRACT ...
The dynamic stall boundaries of a NACA 0012 airfoil oscillating in either the pure plunge mode or... more The dynamic stall boundaries of a NACA 0012 airfoil oscillating in either the pure plunge mode or in the combined pitch and plunge mode is computed using a thin-layer Navier-Stokes solver. Unsteady flowfields are computed at the free-stream Mach number of 0.3, the Reynolds number of 1 • 10 6 , and the Baldwin-Lomax turbulence model is employed. It is found that the pure plunge oscillation leads to dynamic stall as soon as the non-dimensional plunge velocity exceeds the approximate value of 0.35. In addition, the power extraction capability of the airfoil operating in the wingmill mode is studied by computing the dynamic stall boundary for a combined pitch and plunge motion at the reduced frequency values of 0.1, 0.25 and 0.5. Nomenclature c Airfoil chord length (reference length) h Plunge amplitude normalized with c k Reduced frequency (wc/Voo) V<x, Free-stream speed (reference speed) Ofo Pitch amplitude 01 Circular frequency of oscillation (j) Phase shift T Non-dimensional time
In 1947 the U.S. Navy established a Department of Aeronautics in the Naval Postgraduate School in... more In 1947 the U.S. Navy established a Department of Aeronautics in the Naval Postgraduate School in order to better prepare naval aviation officers for the transition from piston engine powered aircraft to gas turbine powered jet aircraft. In 1987 the Department was expanded to cover astronautics. In this paper the educational objectives, programs, and developments in the major areas of concentration are briefly described for the purpose of providing easy access to the Department's history, major accomplishments and current status.
A computational study of flow entrainment over a stationary/flapping airfoil combination in tandem
36th AIAA Aerospace Sciences Meeting and Exhibit, 1998
Unsteady flowfields over a stationary/flapping airfoil combination in tandem are computed using a... more Unsteady flowfields over a stationary/flapping airfoil combination in tandem are computed using a Reynolds averaged Navier-Stokes solver. The stationary leading airfoil has an experimental profile which promotes flow separation at its trailing edge. The effect of the flapping airfoil on the leading airfoil and the flow reattachment at the trailing edge are investigated by varying the amplitude and frequency of the flapping motion. A single deforming C-H type grid and overset grids are employed in the computations. Unsteady flowfields are presented in terms of Mach number contours and time histories of unsteady aerodynamic loads. The high frequency flapping motions, where the experimental data show complete flow reattachment at the trailing edge, could not be performed due to the time step limitation of the solver. However, the flow configurations studied produced a significant amount of flow entrainment at the trailing edge.
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