scholarly journals Unsteady Force Measurements on Fully Wetted Hydrofoils in Heaving Motion

1968 ◽  
Vol 12 (01) ◽  
pp. 69-80
Author(s):  
G. J. Klose ◽  
A. J. Acosta
Keyword(s):  
Theoretical Calculations ◽  
Oscillation Amplitude ◽  
Angle Of Attack ◽  
Two Dimensional ◽  
Force Measurements ◽  
Unsteady Forces ◽  
Reduced Frequency ◽  
Unsteady Force ◽  
Two Dimensional Flow ◽  
Submergence Depth

An experimental investigation is reported of the unsteady forces due to heaving motion of fully wetted hydrofoils of unity aspect ratio and also in two-dimensional flow. The tests covered a broad range of reduced frequency and determined the effects of variation in submergence depth, angle of attack, oscillation amplitude, and flow velocity. In general, the findings agree well with available theoretical calculations, but some unexpected variations were found for the case of a wedge-shaped foil and for changes in angle of attack.

Local Force Measurements on Finite-Span Cylinders in a Cross-Flow

1987 ◽  
Vol 109 (2) ◽  
pp. 136-143 ◽  
Author(s):  
V. K. Sin ◽  
Ronald M. C. So
Keyword(s):  
Free Stream ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Two Dimensional ◽  
Force Measurements ◽  
Unsteady Forces ◽  
Free Stream Turbulence ◽  
Finite Span ◽  
Present Technique ◽  
Unsteady Force

A technique employing a three-axis piezoelectric load cell is developed to measure local unsteady forces induced on cylinders placed in a cross flow. Verification of the technique is carried out with a two-dimensional circular cylinder. All measurements are made at a Reynolds number of ∼4.8 × 104 and a free-stream turbulence of ∼1.5 percent. The local two-dimensional unsteady lift measurement is found to be in excellent agreement with spanwise-averaged data reported in the literature, thereby validating the feasibility of the present technique. Steady and unsteady force measurements on finite-span circular cylinders are reported and compared with available data in the literature.

scholarly journals Scaling the propulsive performance of heaving and pitching foils

2017 ◽  
Vol 822 ◽  
pp. 386-397 ◽  
Author(s):  
Daniel Floryan ◽  
Tyler Van Buren ◽  
Clarence W. Rowley ◽  
Alexander J. Smits
Keyword(s):  
Strouhal Number ◽  
Linear Dependence ◽  
Scaling Laws ◽  
Biological Data ◽  
Viscous Drag ◽  
Water Tunnel ◽  
Two Dimensional ◽  
Propulsive Performance ◽  
Reduced Frequency ◽  
Two Dimensional Flow

Scaling laws for the propulsive performance of rigid foils undergoing oscillatory heaving and pitching motions are presented. Water tunnel experiments on a nominally two-dimensional flow validate the scaling laws, with the scaled data for thrust, power and efficiency all showing excellent collapse. The analysis indicates that the behaviour of the foils depends on both Strouhal number and reduced frequency, but for motions where the viscous drag is small the thrust closely follows a linear dependence on reduced frequency. The scaling laws are also shown to be consistent with biological data on swimming aquatic animals.

A Comparison of Forces in Two- and Three-Dimensional Flow Past an Oscillating Cylinder

2015 ◽  
Author(s):  
Sofia Peppa ◽  
Lambros Kaiktsis ◽  
Christos Frouzakis ◽  
George Triantafyllou
Keyword(s):  
Stokes Equations ◽  
Oscillation Amplitude ◽  
Three Dimensional ◽  
Oscillation Mode ◽  
Transverse Oscillation ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Past ◽  
Two Dimensional Flow

DNS results are presented for three-dimensional flow past a circular cylinder forced to oscillate both in the transverse and in-line direction with respect to a uniform stream, at Reynolds number equal to 400, and are compared against simulation results for two-dimensional flow. The cylinder follows a figure-eight motion, traversed either counter-clockwise or clockwise in the upper half-plane for a flow stream from left to right. The transverse oscillation frequency is equal to the natural frequency of the Kármán vortex street. The Navier-Stokes equations are solved using a spectral element code, and the forces acting on the cylinder are computed for both three- and two-dimensional flow. The results demonstrate that the effect of cylinder oscillation on the flow structure and forces differs substantially between the counter-clockwise and the clockwise oscillation mode. For the counter-clockwise mode, forcing at low amplitude decreases the flow three-dimensionality, with the wake becoming increasingly three-dimensional for transverse oscillation amplitudes higher than 0.25–0.30 cylinder diameters, with corresponding discrepancies in forces with respect to two-dimensional flow. For the case of clockwise mode, a strong stabilizing effect is found: the wake becomes two-dimensional for a transverse oscillation amplitude of 0.20 cylinder diameters, and remains so at higher amplitudes, resulting in nearly equal values of the force coefficients for three- and two-dimensional flow.

scholarly journals Two-dimensional flow of foam around an obstacle: Force measurements

2005 ◽  
Vol 71 (3) ◽  
Author(s):  
Benjamin Dollet ◽  
Florence Elias ◽  
Catherine Quilliet ◽  
Christophe Raufaste ◽  
Miguel Aubouy ◽  
...  
Keyword(s):  
Two Dimensional ◽  
Force Measurements ◽  
Dimensional Flow ◽  
Two Dimensional Flow

scholarly journals An Improved Nonlinear Aerodynamic Derivative Model of Aircraft at High Angles of Attack

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Mi Baigang ◽  
Yu Jingyi
Keyword(s):  
Oscillation Amplitude ◽  
Angle Of Attack ◽  
Aerodynamic Characteristics ◽  
Higher Order ◽  
Initial Angle ◽  
Prediction Ability ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency ◽  
High Angles Of Attack ◽  
Nonlinear Aerodynamic

The classical aerodynamic derivative model is widely used in flight dynamics, but its application is extremely limited in cases with complicated nonlinear flows, especially at high angles of attack. A modified nonlinear aerodynamic derivative model for predicting unsteady aerodynamic forces and moments at a high angle of attack is developed in this study. We first extend the higher-order terms to describe the nonlinear characteristics and then introduce three more influence parameters, the initial angle of attack, the reduced frequency, and the oscillation amplitude, to correct the constant aerodynamic derivative terms that have higher-order polynomials for these values. The improved nonlinear aerodynamic derivative model was validated by using the NACA 0015 airfoil and the F-18 model. The results show that the improved model has a higher prediction ability at high angles of attack and has the ability to predict the aerodynamic characteristics of other unknown states based on known unsteady aerodynamic data, such as the initial angle of attack, reduced frequency, and oscillation amplitude.

scholarly journals Unsteady force measurements on propeller model in cavitation tunnels

2021 ◽  
Vol 4 (398) ◽  
pp. 61-67
Author(s):  
Igor Solovyev ◽  
◽  
Andrey Yermolayev ◽  
Keyword(s):  
Test Data ◽  
Model Test ◽  
Model Testing ◽  
Load Cell ◽  
Force Measurements ◽  
Unsteady Forces ◽  
Cavitation Tunnel ◽  
Unsteady Force ◽  
Metrological Performance ◽  
Metrological Parameters

Object and purpose of research. This paper discusses longitudinal unsteady force dynamometer for cavitation tunnel tests. The purpose of the study is to improve metrological performance of the dynamometer and extend the scope of its application. Materials and methods. The study is based on metrological parameters of dynamometers and model test data available with KSRC Large Cavitation Tunnel (LCT). Main results. Development, manufacturing, certification and commissioning of longitudinal unsteady force dynamometer based on piezoceramic load cell with improved metrological performance making it applicable for model testing of not only propellers but also other types of marine propulsors. Conclusion. Dynamometer with piezoceramic load cell offers more accurate measurement of unsteady forces, wider band of measurement frequencies, as well as wider spectrum of possible applications and lower susceptibility to interference.

scholarly journals Cavity flow past a slender pointed hydrofoil

1961 ◽  
Vol 11 (2) ◽  
pp. 187-208 ◽  
Author(s):  
E. Cumberbatch ◽  
T. Y. Wu
Keyword(s):  
Angle Of Attack ◽  
Cross Flow ◽  
The Body ◽  
Two Dimensional ◽  
Cross Sectional ◽  
Slender Body Theory ◽  
Flow Past ◽  
Two Dimensional Flow ◽  
Cavity Boundary ◽  
The Cross

A slender-body theory for the flow past a slender, pointed hydrofoil held at a small angle of attack to the flow, with a cavity on the upper surface, has been worked out. The approximate solution valid near the body is seen to be the sum of two components. The first consists of a distribution of two-dimensional sources located along the centroid line of the cavity to represent the variation of the cross-sectional area of the cavity. The second component represents the cross-flow perpendicular to the centroid line. It is found that over the cavity boundary which envelops a constant pressure region, the magnitude of the cross-flow velocity is not constant, but varies to a moderate extent. With this variation neglected only in the neighbourhood of the hydrofoil, the cross-flow is solved by adopting the Riabouchinsky model for the two-dimensional flow. The lift is then calculated by intergrating the pressure along the chord; the dependence of the lift on cavitation number and angle of attack is shown for a specific case of the triangular plan form.

scholarly journals Study on Thin Airfoil Theory & Performance Test of Elliptical Wing as Compared to Model Mosquito Wing and NACA 64A012 Mod Airfoil

2018 ◽  
Vol 3 (4) ◽  
pp. 48
Author(s):  
Nesar Ali ◽  
Mostafizur Rahman Komol ◽  
Mohammad Takiuddin Saki
Keyword(s):  
Performance Test ◽  
Center Of Pressure ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Simulation Software ◽  
Two Dimensional ◽  
Dimensional Flow ◽  
Thin Airfoil ◽  
Two Dimensional Flow

Thin airfoil theory is a simple conception of airfoils that describes angle of attack to lift for incompressible, inviscid flows. It was first devised by famous German-American mathematician Max Munk and therewithal refined by British aerodynamicist Hermann Glauertand others in the 1920s. The thin airfoil theory idealizes that the flow around an airfoil as two-dimensional flow around a thin airfoil. It can be conceived as addressing an airfoil of zero thickness and infinite wingspan. Thin airfoil theory was particularly citable in its day because it provided a well-established theoretical basis for the following important prominence of airfoils in two-dimensional flow like i) on a symmetric shape of airfoil which center of pressure and aerodynamic center remain exactly one quarter of the chord behind the leading edge, ii) on a cambered airfoil, the aerodynamic center lies exactly one quarter of the chord behind the leading edge and iii)the slope of the lift coefficient versus angle of attack line is two pi ( ) units per radian. The fundamental equation of Prandtl’s lifting-line theory; simply states that the geometric angle of attack is equal to the sum of the effective angle plus the induced angle of attack. And also omitted the theory of elliptical wing theory which indicates that the Elliptical wing has better flight performance than any other airfoil. In this experiment we made a model of elliptical wing and test in wind tunnel to get experimental value. We also analyze the model in simulation software for further knowledge. Comparing this practical and experimental value to other airfoil like Mosquito wing and NACA 64A012 airfoil for further research.

Unsteady force generation and vortex dynamics of pitching and plunging aerofoils

2012 ◽  
Vol 709 ◽  
pp. 37-68 ◽  
Author(s):  
Yeon Sik Baik ◽  
Luis P. Bernal ◽  
Kenneth Granlund ◽  
Michael V. Ol
Keyword(s):  
Strouhal Number ◽  
Vortex Dynamics ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Reduced Frequency ◽  
Unsteady Force ◽  
Edge Vortex ◽  
Effective Angle ◽  
Flow Evolution

AbstractExperimental studies of the flow topology, leading-edge vortex dynamics and unsteady force produced by pitching and plunging flat-plate aerofoils in forward flight at Reynolds numbers in the range 5000–20 000 are described. We consider the effects of varying frequency and plunge amplitude for the same effective angle-of-attack time history. The effective angle-of-attack history is a sinusoidal oscillation in the range $\ensuremath{-} 6$ to $2{2}^{\ensuremath{\circ} } $ with mean of ${8}^{\ensuremath{\circ} } $ and amplitude of $1{4}^{\ensuremath{\circ} } $. The reduced frequency is varied in the range 0.314–1.0 and the Strouhal number range is 0.10–0.48. Results show that for constant effective angle of attack, the flow evolution is independent of Strouhal number, and as the reduced frequency is increased the leading-edge vortex (LEV) separates later in phase during the downstroke. The LEV trajectory, circulation and area are reported. It is shown that the effective angle of attack and reduced frequency determine the flow evolution, and the Strouhal number is the main parameter determining the aerodynamic force acting on the aerofoil. At low Strouhal numbers, the lift coefficient is proportional to the effective angle of attack, indicating the validity of the quasi-steady approximation. Large values of force coefficients (${\ensuremath{\sim} }6$) are measured at high Strouhal number. The measurement results are compared with linear potential flow theory and found to be in reasonable agreement. During the downstroke, when the LEV is present, better agreement is found when the wake effect is ignored for both the lift and drag coefficients.

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