Force and Moment Measurements of Supercavitating Hydrofoils of Finite Span With Comparison to Theory

1975 ◽  
Vol 97 (4) ◽  
pp. 453-462
Author(s):  
P. Leehey ◽  
T. S. Stellinger
Keyword(s):  
Aspect Ratio ◽  
Asymptotic Expansions ◽  
Cavity Length ◽  
Large Aspect Ratio ◽  
Drag Coefficients ◽  
Finite Span ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Lift And Drag ◽  
Good Agreement

Measurements were made of lift, drag, and moment coefficients, and cavity length for aspect ratio 3 and 5 supercavitating hydrofoils of elliptical planform. These measurements are compared with theoretical predictions obtained from matching asymptotic expansions for large aspect ratio. Good agreement was obtained for lift and drag coefficients for angles of attack from 10 deg to 15 deg and for a wide range of cavity lengths. Theoretical moment coefficients were too large indicating the need for lifting surface corrections.

Two-Dimensional Base-Vented Hydrofoils Near a Free Surface: Influence of the Ventilation Number

1975 ◽  
Vol 97 (4) ◽  
pp. 465-473 ◽  
Author(s):  
A. Rowe ◽  
J. M. Michel
Keyword(s):  
Free Surface ◽  
Asymptotic Expansions ◽  
Constant Coefficient ◽  
Cavity Length ◽  
Matched Asymptotic Expansions ◽  
Two Dimensional ◽  
Drag Coefficients ◽  
Lift And Drag ◽  
Limiting Values

The method of matched asymptotic expansions is used to analyze the flow around a base-vented lifting foil with rounded nose beneath a free surface. The foil is defined numerically. Results concerning the lift and drag coefficients and the limiting values of incidences without cavitation are compared with experiments. The relation between the cavity length and the ventilation number at several depths of submergence is given in the case of a symmetrical wedge: it agrees with the experimental one except by a nearly constant coefficient.

A Model for the Coupled Lift and Drag on a Circular Cylinder

2003 ◽  
Author(s):  
Ali H. Nayfeh ◽  
Farouk Owis ◽  
Muhammad R. Hajj
Keyword(s):  
Circular Cylinder ◽  
Stokes Equations ◽  
Quadratic Function ◽  
Phase Relations ◽  
Suitable Model ◽  
Van Der Pol ◽  
Spectral Moments ◽  
Drag Coefficients ◽  
Wide Range ◽  
Lift And Drag

The time-varying coupled lift and drag coefficients acting on a circular cylinder are modeled. Data used for the model are obtained by numerically solving the unsteady Reynolds-Averaged Navier Stokes equations over a wide range of Reynolds numbers. Using spectral moments, we determine the frequency components in the lift and drag coefficients and their phase relations. Using a perturbation technique, we obtain approximate solutions of both the van der Pol and Rayleigh equations. By fitting the amplitude and phase relations, we find that the van der Pol equation is the suitable model for the lift. The Rayleigh equation fails to give the correct phase relation. Because the major frequency in the drag component is twice that of the lift, the drag component is modeled as a quadratic function of the lift. Through analysis with higher-order spectral moments, the correct quadratic relation of the lift that yields the drag is determined. The model and results presented here are a first step in the development of a reduced-order model for vortex-induced vibrations, which includes the motions of the cylinder.

scholarly journals Effect of Aspect Ratio on Lift and Drag Coefficients of Cambered Plates

2000 ◽  
Vol 66 (1) ◽  
pp. 97-103 ◽  
Author(s):  
Kengo Fukuda ◽  
Fuxiang Hu ◽  
Tadashi Tokai ◽  
Ko Matuda
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficients ◽  
Lift And Drag

Steady Compressible Flow through a Single Row of Radial Holes in the Wall of a Pipeline

1970 ◽  
Vol 12 (4) ◽  
pp. 248-258 ◽  
Author(s):  
G. H. Trengrouse
Keyword(s):  
Discharge Coefficient ◽  
Pressure Change ◽  
Single Row ◽  
One Dimensional ◽  
Discharge Coefficients ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Flow Through ◽  
Flow Theories ◽  
Good Agreement

Measured values of discharge coefficient for air flow through a single row of radial holes in the wall of a pipeline are reported, together with the values of pipe Mach numbers in the immediate vicinity of the holes. A wide range of pressure and area ratios are considered, the flow through the holes being either into or out of the pipe. It is shown that the effects on the measured values of both the pressure level at discharge from the holes and the air temperature are negligible. The agreement between the pressure change in the pipeline due to the holes, obtained experimentally, and that predicted by simple, one-dimensional flow theories is generally unsatisfactory. However, theoretical predictions of the jet efflux angles based on two-dimensional, incompressible, non-viscous flow arguments are in good agreement with those measured, but discrepancies do arise in the prediction of discharge coefficients.

Analysis of the Flow Characteristics of Two Nonrotating Rotor Blades

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
R. P. J. O. M. van Rooij
Keyword(s):  
Aspect Ratio ◽  
Dominant Role ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Rotor Blades ◽  
Drag Coefficients ◽  
Wing Model ◽  
Stall Angle ◽  
Twisted Blade ◽  
Lift And Drag

The investigation focuses on the analysis of the airfoil segment performances along rotor blades in the parked configuration. In this research, wind tunnel experiments on two twisted blade geometries with different airfoils played a dominant role. These measurements were carried out by the Swedish Aeronautical Research Institute, former FFA, and by the American National Renewable Energy Laboratories (NREL) during the Unsteady Aerodynamic Experiment. The spans of the blades were 2.375m and 5m, the STORK 5 WPX and the NREL Phase VI blade, respectively. Five span locations (inboard, midspan, outboard, and tip regions) were considered and compared with the 2D airfoil characteristics. Wing model experiments with similar blade aspect ratio were included in the research. Furthermore, the commercial computational fluid dynamics code FLUENT was used for the validation and analysis of the spanwise lift and drag coefficients at four different pitch settings, 20deg, 30deg, 45deg, and 60deg. The computed pressure distributions compared reasonably well, but the derived lift and drag showed quite some differences with the blade measurements. The lift coefficients for the sections beyond the leading-edge stall angle of the STORK blade were larger than for the NREL blade and were close to that of a wing model with similar airfoil and aspect ratio. Lift and drag coefficients for the sections of the two blades were always much smaller than the 2D results. The drag values for both blades showed quite some agreement, and airfoil and blade dependency seemed to be small.

Numerical Studies of Magnetohydrostatic Finite-Beta Stellarator Equilibria

1982 ◽  
Vol 37 (8) ◽  
pp. 879-890 ◽  
Author(s):  
F. Herrnegger
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Pressure Profile ◽  
Large Aspect Ratio ◽  
Weak Effect ◽  
Numerical Convergence ◽  
Secondary Currents ◽  
Numerical Studies ◽  
Critical Equilibrium ◽  
Theoretical Predictions

Properties of finite-beta stellarator equilibria are investigated which are obtained as fully three-dimensional finite-beta solutions of the magnetohydrostatic boundary value problem with the help of the code by Bauer, Betancourt, and Garabedian based on the energy method. In the case of slender l = 2 stellarator equilibria the displacement of the magnetic axis as well as its helical deformation as functions of beta are found to be close to the known theoretical predictions which were derived for slender low beta l = 2 configurations of large aspect ratio. In the case of l = 2 stellarators with moderate aspect ratio the shear has a weak effect on the displacement in contradiction to results from asymptotic theories. A class of l = 0, 1, 2, 3 configurations with reduced secondary currents could be found showing axis displacements which are at least a factor of three smaller than those in pure l = 2 stellarators. A critical equilibrium beta value of βe(0) = 0.045 has been estimated in the W VII-AS stellarator for a bell-shaped pressure profile. Extensive numerical convergence studies are presented

Stiffness and Bond Strength of Rubber-Filled Hinges

1993 ◽  
Vol 66 (5) ◽  
pp. 733-741 ◽  
Author(s):  
A. N. Gent ◽  
Y-W. Chang
Keyword(s):  
Finite Element Analysis ◽  
Bond Strength ◽  
Direct Analysis ◽  
Test Method ◽  
Bond Rupture ◽  
Experimental Measurements ◽  
Element Analysis ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Good Agreement

Abstract The stiffness of rubber-filled hinges for small rotations of the hinge plates has been determined by finite element analysis (FEA). The rubber is assumed to be linearly elastic and virtually incompressible, and the hinge is assumed to be long enough for the rubber to be in a state of plane strain, i.e., prevented from any displacement parallel to the hinge. Results have been obtained for hinges of a wide range of unstrained angle, ranging from 5° up to 360°. The calculated stiffnesses for long hinges vary by over four orders of magnitude over this range. For small angles, an approximate solution has been obtained by direct analysis—it is in good agreement with the FEA solution for hinge angles up to about 40°. Experimental measurements on several rubber-filled hinges are also reported. The measured rotational stiffnesses are in satisfactory agreement with theoretical predictions. Because a rubber-filled hinge constitutes a possible test method for bond strength, conditions are derived for bond rupture as a hinge is strained open.

Dynamic Behavior of Spherical Friction Dampers and Its Implication to Damper Contact Stiffness

2006 ◽  
Vol 129 (2) ◽  
pp. 511-521 ◽  
Author(s):  
K-H. Koh ◽  
J. H. Griffin
Keyword(s):  
Contact Stiffness ◽  
Friction Damper ◽  
Test Fixture ◽  
Friction Dampers ◽  
Vibratory Response ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Vibrating Systems ◽  
Good Agreement ◽  
Mindlin’S Theory

A model that predicts the quasi-static behavior of a friction damper that has spherical contacts was developed using Mindlin’s theory. The model was integrated into a dynamic analysis that predicts the vibratory response of frictionally damped blades. The analytical approach was corroborated through a set of benchmark experiments using a blades/damper test fixture. There was good agreement between the theoretical predictions of amplitude and the values that were measured experimentally over a wide range of test conditions. It is concluded that it is possible to predict the vibratory response of frictionally damped vibrating systems using continuum mechanics, provided that the contact geometry is clearly defined and the local nonlinear contact is correctly taken into account.

An Experimental Study of Confined Masonry Walls with Varying Aspect Ratios

2015 ◽  
Vol 31 (2) ◽  
pp. 945-968 ◽  
Author(s):  
J. J. Perez Gavilan ◽  
L. E. Flores ◽  
S. M. Alcocer
Keyword(s):  
Aspect Ratio ◽  
Good Accuracy ◽  
Axial Stress ◽  
Masonry Walls ◽  
Inelastic Behavior ◽  
Ductility Demand ◽  
Confined Masonry ◽  
Aspect Ratios ◽  
Wide Range ◽  
Good Agreement

Results from an experimental series of seven full-scale confined masonry walls with height-to-length aspect ratios ( H/L) from 0.3 up to 2.2 are summarized. Results show that neither the level of axial stress nor the aspect ratio had a significant effect on lateral stiffness. Inelastic behavior of the walls, characterized by normalized stiffness degradation with ductility demand, can be estimated with good accuracy with a bilinear function for a ductility demand up to 4.5. A substantial increase in normalized shear strength was observed for walls with decreasing aspect ratio. A correction factor to the nominal cracking strength was deduced based on differences of the flexural deformations for squat and square walls. The factor was then compared to the experimental normalized strength with good agreement. A new expression for inclined cracking shear that can be used for a wide range of wall aspect ratios is proposed.

Laminar secondary flows in curved rectangular ducts

1990 ◽  
Vol 217 ◽  
pp. 421-440 ◽  
Author(s):  
S. Thangam ◽  
N. Hur
Keyword(s):  
Aspect Ratio ◽  
Secondary Flow ◽  
Vortex Pair ◽  
Stability Diagram ◽  
Secondary Flows ◽  
Dean Number ◽  
Single Vortex ◽  
Curvature Ratio ◽  
Wide Range ◽  
Good Agreement

The occurrence of secondary flow in curved ducts due to the centrifugal forces can often significantly influence the flow rate. In the present work, the secondary flow of an incompressible viscous fluid in a curved duct is studied by using a finite-volume method. It is shown that as the Dean number is increased the secondary flow structure evolves into a double vortex pair for low-aspect-ratio ducts and roll cells for ducts of high aspect ratio. A stability diagram is obtained in the domain of curvature ratio and Reynolds number. It is found that for ducts of high curvature the onset of transition from single vortex pair to double vortex pair or roll cells depends on the Dean number and the curvature ratio, while for ducts of small curvature the onset can be characterized by the Dean number alone. A comparison with the available theoretical and experimental results indicates good agreement. A correlation for the friction factor as a function of the Dean number and aspect ratio is developed and is found to be in good agreement with the available experimental and computational results for a wide range of parameters.

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