Hydrofoil Drag Reduction by Partial Cavitation

2006 ◽  
Vol 128 (5) ◽  
pp. 931-936 ◽  
Author(s):  
Eduard Amromin ◽  
Jim Kopriva ◽  
Roger E. A. Arndt ◽  
Martin Wosnik
Keyword(s):  
Drag Reduction ◽  
Lift Coefficient ◽  
Design Procedure ◽  
Suction Side ◽  
Operating Regime ◽  
Cavitation Number ◽  
Partial Cavitation ◽  
Lift And Drag ◽  
Naca 0015 ◽  
Drag Ratio

Partial cavitation reduces hydrofoil friction, but a drag penalty associated with unsteady cavity dynamics usually occurs. With the aid of inviscid theory a design procedure is developed to suppress cavity oscillations. It is demonstrated that it is possible to suppress these oscillations in some range of lift coefficient and cavitation number. A candidate hydrofoil, denoted as OK-2003, was designed by modification of the suction side of a conventional NACA-0015 hydrofoil to provide stable drag reduction by partial cavitation. Validation of the design concept with water tunnel experiments has shown that the partial cavitation on the suction side of the hydrofoil OK-2003 does lead to drag reduction and a significant increase in the lift to drag ratio within a certain range of cavitation number and within a three-degree range of angle of attack. Within this operating regime, fluctuations of lift and drag decrease down to levels inherent to cavitation-free flow. The favorable characteristics of the OK-2003 are compared with the characteristics of the NACA-0015 under cavitating conditions.

An Extended Linearized Inverse Theory for Fully Cavitating Hydrofoil Section Design

1979 ◽  
Vol 23 (04) ◽  
pp. 260-271
Author(s):  
Blaine R. Parkin ◽  
Joe Fernandez
Keyword(s):  
Design Theory ◽  
Parametric Design ◽  
Lift Coefficient ◽  
Design Procedure ◽  
Cavitation Number ◽  
Inverse Theory ◽  
Cavity Surface ◽  
Moment Coefficient ◽  
Section Design ◽  
Cavity Thickness

A new design theory for fully cavitating hydrofoils is based upon a linearized inverse theory of two-dimensional cavity flows at arbitrary cavitation number. The cavity surfaces are assumed to originate at the leading and trailing edges of the wetted surface. This paper reviews and completes the basic theory, which leads to a parametric design technique. In the resulting design procedure, one specifies the design lift coefficient, the cavitation number and the upper cavity thickness at two points along the profile chord. A prescribed pressure distribution shape is also selected. These quantities determine the profilelesgn, which consists of the upper cavity and wetted surface contours, the design angle of attack, the cavity length, the drag coefficient, the moment coefficient and the lift-to-drag ratio. The chief new feature of the third design procedure is that the designer can now prescribe two points on the cavity surface instead of one as heretofore. Although the designer must observe certain constraints when he specifies these two values of cavity thickness, the new procedure is still found to be more general and more flexible than design procedures studied previously.

Supercavitating Foils With Flaps Beneath a Free Surface

1964 ◽  
Vol 86 (2) ◽  
pp. 197-204
Author(s):  
J. Auslaender
Keyword(s):  
Free Surface ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Cavitation Number ◽  
Operating Conditions ◽  
Mapping Technique ◽  
Moment Coefficient ◽  
Lift Curve ◽  
Flap Deflection ◽  
Drag Ratio

Linearized airfoil theory—in conjunction with a mapping technique—is applied to the calculation of the forces and moments acting on supercavitating hydrofoils operating near a free surface at very large Froude numbers and zero cavitation number. Only the effects of angle of attack and flap deflection are considered. The results—intended for engineering use—are presented primarily in the form of curves of flap effectiveness, lift curve slope, pitching and hinge moment coefficient, and flap loading versus flap-chord ratio, depth being introduced as a parameter. Lift-drag ratio and hinge moment coefficient as functions of lift coefficient are presented for typical operating conditions.

scholarly journals Aerodynamic Performance of Biomimicry Snake-Shaped Airfoil

2019 ◽  
Vol 9 (2) ◽  
pp. 3319-3323
Keyword(s):  
Cross Section ◽  
Lift Coefficient ◽  
Design Parameters ◽  
Drag Forces ◽  
Cross Section Shape ◽  
Section Shape ◽  
Wide Range ◽  
Lift And Drag ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The cross-section shape and proportionality between geometrical dimensions are the most important design parameters of any lifting surfaces. These parameters affect the amount of the aerodynamic forces that will be generated. In this study, the focus is placed on the snake-cross-section airfoil known as the S-airfoil. It is found that there is a lack of available researches on S-airfoil despite its important characteristics. A parametric study on empty model of the S-airfoil with a cross-section shape that is inspired by the Chrysopelea paradise snake is conducted through numerical simulation. Simulation using 2D-ANSYS FLUENT17 software is used to generate the lift and drag forces to determine the performance of airfoil aerodynamic. Based on the results, the S-airfoil can be improved in performance of aerodynamic by reducing the thickness at certain range, whereby changing the thickness-to-chord ratio from 0.037 to 0.011 results in the increment of lift-to-drag ratio from 2.629 to 3.257. On other hand, increasing the height-to-chord ratio of the S-airfoil will increase maximum lift coefficient but drawback is a wide range of angles of attack regarding maximum lift-to-drag ratio. Encouraging results obtained in this study draws attention to the importance of expanding the research on S-airfoil and its usage, especially in wind energy.

Hydrodynamic Trends from a Generalized Design Procedure for Fully Cavitating Hydrofoil Sections

1979 ◽  
Vol 23 (04) ◽  
pp. 272-283
Author(s):  
Blaine R. Parkin ◽  
Joe Fernandez
Keyword(s):  
Parametric Design ◽  
Lift Coefficient ◽  
Design Procedure ◽  
Feasibility Studies ◽  
Cavitation Number ◽  
Hydrodynamic Performance ◽  
Cavity Surface ◽  
Cavity Flows ◽  
Moment Coefficient ◽  
Cavity Thickness

An extended design procedure for fully cavitating hydrofoils is based upon a linearized inverse theory of two-dimensional cavity flows at arbitrary cavitation number. The cavity surfaces are assumed to originate at the leading and trailing edges of the wetted surface. This paper completes the basic theory and gives detailed examples obtained from the resulting parametric design technique. In this procedure, one specifies the design lift coefficient, the cavitation number and the upper cavity thickness at two points along the profile chord. A prescribed pressure distribution shape is also selected. These quantities determine the profile design, which consists of the upper cavity and wetted surface contours, the design angle of attack, the cavity length, the drag coefficient, the moment coefficient and the lift-to-drag ratio. The method also includes off-design calculations in accordance with the direct theory of cavity flows, which determines the flow states for which interference can occur between the upper surface of the cavity and the upper nonwetted surface of the profile. The hydrodynamic performance of specific "point designs" is also given by these direct calculations. The chief new feature of the generalized design procedure is that it gives a designer the ability to prescribe two points on the cavity surface instead of one as heretofore. Although certain constraints must be observed by the designer when specifying these two values of cavity thickness, the third procedure is found to be more general and more flexible than design procedures studied previously. The necessary constraints are incorporated in the computer logic for the method. The fact that linearized theory is used tends to limit the applicability of the method to conceptual design and feasibility studies. The computer program for the procedure has been found to be economical and well suited for its intended purpose.

The Effects of Recessed Lower Surface Shape on the Lift and Drag of Conical Wings at High Incidence and High Mach Number

1975 ◽  
Vol 26 (1) ◽  
pp. 1-10 ◽  
Author(s):  
L C Squire
Keyword(s):  
Theoretical Study ◽  
Lift Coefficient ◽  
Lower Surface ◽  
Surface Shape ◽  
Wide Range ◽  
High Incidence ◽  
Design Value ◽  
High Mach ◽  
Lift And Drag ◽  
Drag Ratio

SummaryFor lifting re-entry there may be advantages in using wings which give as high a lift coefficient as possible at the design value of the lift/drag ratio. This paper presents the results of an experimental and theoretical study of wings with recessed lower surfaces designed to give high values of CL. The calculations show that a wide range of wing shapes can be found that give values of CL which are much larger than those on a flat wing with the same lift/drag ratio.

scholarly journals Effect of the Backward-Facing Step Location on the Aerodynamics of a Morphing Wing

2021 ◽  
Author(s):  
Fadi Magdy R Mishriky ◽  
Paul Walsh
Keyword(s):  
Drag Coefficient ◽  
Transition Point ◽  
Numerical Study ◽  
Lift Coefficient ◽  
Suction Side ◽  
Backward Facing Step ◽  
Viscous Boundary Layer ◽  
Airfoil Surface ◽  
Aerodynamic Properties ◽  
Lift And Drag

Over the last decade, aircraft morphing technology has drawn a lot of attention in the aerospace community, because it is likely to improve the aerodynamic performance and the versatility of aircraft at different flight regimes. With the fast paced advancements in this field, a parallel stream of research is studying different materials and designs to develop reliable morphing skins. A promising candidate for a viable morphing skin is the sliding skin, where two or more rigid surfaces remain in contact and slide against each other during morphing. The overlapping between each two panels create a backward-facing step on the airfoil surface which has a critical effect on the aerodynamics of the wing. This paper presents a numerical study of the effect of employing a backward-facing step on the suction side of a National Advisory Committee for Aeronautics (NACA) 2412 airfoil at a high Reynolds number of 5.9 × 106. The effects of the step location on the lift coefficient, drag coefficient and critical angle of attack are studied to find a favorable location for the step along the chord-wise direction. Results showed that employing a step on the suction side of the NACA 2412 airfoil can adversely affect the aforementioned aerodynamic properties. A drop of 21.1% in value of the lift coefficient and an increase of 120.8% in the drag coefficient were observed in case of a step located at 25% of the chord length. However, these effects are mitigated by shifting the step location towards the trailing edge. Introducing a step on the airfoil caused the airfoil’s thickness to change, which in turn has affected the transition point of the viscous boundary layer from laminar to turbulent. The location of the step, prior or post the transition point, has a noteworthy effect on the pressure and shear stress distribution, and consequently on the values of the lift and drag coefficients.

scholarly journals Effect of the Backward-Facing Step Location on the Aerodynamics of a Morphing Wing

2021 ◽  
Author(s):  
Rshare Library ◽  
Fadi Magdy R Mishriky ◽  
Paul Walsh
Keyword(s):  
Drag Coefficient ◽  
Transition Point ◽  
Numerical Study ◽  
Lift Coefficient ◽  
Suction Side ◽  
Backward Facing Step ◽  
Viscous Boundary Layer ◽  
Airfoil Surface ◽  
Aerodynamic Properties ◽  
Lift And Drag

Over the last decade, aircraft morphing technology has drawn a lot of attention in the aerospace community, because it is likely to improve the aerodynamic performance and the versatility of aircraft at different flight regimes. With the fast paced advancements in this field, a parallel stream of research is studying different materials and designs to develop reliable morphing skins. A promising candidate for a viable morphing skin is the sliding skin, where two or more rigid surfaces remain in contact and slide against each other during morphing. The overlapping between each two panels create a backward-facing step on the airfoil surface which has a critical effect on the aerodynamics of the wing. This paper presents a numerical study of the effect of employing a backward-facing step on the suction side of a National Advisory Committee for Aeronautics (NACA) 2412 airfoil at a high Reynolds number of 5.9 × 106. The effects of the step location on the lift coefficient, drag coefficient and critical angle of attack are studied to find a favorable location for the step along the chord-wise direction. Results showed that employing a step on the suction side of the NACA 2412 airfoil can adversely affect the aforementioned aerodynamic properties. A drop of 21.1% in value of the lift coefficient and an increase of 120.8% in the drag coefficient were observed in case of a step located at 25% of the chord length. However, these effects are mitigated by shifting the step location towards the trailing edge. Introducing a step on the airfoil caused the airfoil’s thickness to change, which in turn has affected the transition point of the viscous boundary layer from laminar to turbulent. The location of the step, prior or post the transition point, has a noteworthy effect on the pressure and shear stress distribution, and consequently on the values of the lift and drag coefficients.

Comparison of Hydrofoil Drag Reduction by Natural and Ventilated Partial Cavitation

2005 ◽  
Author(s):  
Jim Kopriva ◽  
Roger E. A. Arndt ◽  
Martin Wosnik ◽  
Eduard Amromin
Keyword(s):  
Cavitation Number ◽  
Water Tunnel ◽  
Cavity Pressure ◽  
Cavitating Flows ◽  
Ventilated Cavitation ◽  
Promising Tool ◽  
Partial Cavitation ◽  
Natural Cavitation ◽  
Direct Pressure ◽  
Drag Ratio

The theory of cavitation in an ideal fluid is utilized to design hydrofoils that have a significant increase of lift to drag ratio for a regime of partially cavitating flows. Our recently reported experiments with natural cavitation have confirmed the existence of such an increase within a certain range of cavitation number and angle of attack for the specially designed hydrofoil designated as OK-2003. For applications of such a design to engineering, it would be necessary to keep the cavitation number within this favorable range and ventilation looks to be the most promising tool for control of cavitating flows. Therefore, comparative water tunnel tests have been carried out for both natural and ventilated cavitation of the OK-2003. The general similarity between the two kinds of partial cavitation for the developed low-drag hydrofoil is proven. When validating theory with the aid of water tunnel experiments, a general issue of how to make a comparison between natural cavitation and ventilated cavitation was encountered. This issue is the difficulty to determine the pressure within partial cavities. During natural cavitation the cavity pressure can deviate from vapor pressure due to the effects of dissolved gas and possibly other water quality effects. Direct pressure measurements within the partial cavity have proved to be unstable due to the unsteadiness of the cavity. The unsteadiness effect becomes more dominant as cavitation number is increased and the cavity becomes smaller. There is a point where the measured cavity pressure becomes unusable. In the case of ventilated cavitation, the interaction of the airflow with the surface of relatively thin cavities can be significant. Finally, it was experimentally determined that different dynamics of cavity pulsation are inherent to natural and ventilated cavitation.

scholarly journals Shape Optimization of NREL S809 Airfoil for Wind Turbine Blades Using a Multiobjective Genetic Algorithm

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Yilei He ◽  
Ramesh K. Agarwal
Keyword(s):  
Genetic Algorithm ◽  
Wind Turbine ◽  
Lift Coefficient ◽  
Optimization Technique ◽  
Turbine Blades ◽  
Wind Turbine Blades ◽  
Multiobjective Genetic Algorithm ◽  
Lift And Drag ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The goal of this paper is to employ a multiobjective genetic algorithm (MOGA) to optimize the shape of a well-known wind turbine airfoil S809 to improve its lift and drag characteristics, in particular to achieve two objectives, that is, to increase its lift and its lift to drag ratio. The commercially available software FLUENT is employed to calculate the flow field on an adaptive structured mesh using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a two-equationk-ωSST turbulence model. The results show significant improvement in both lift coefficient and lift to drag ratio of the optimized airfoil compared to the original S809 airfoil. In addition, MOGA results are in close agreement with those obtained by the adjoint-based optimization technique.

scholarly journals Lift and Drag Coefficient Map of NACA4415 Airfoil

2021 ◽  
Vol 2076 (1) ◽  
pp. 012066
Author(s):  
Rui Yin ◽  
Jing Huang ◽  
Zhi-Yuan He
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Aerodynamic Characteristics ◽  
Optimal Angle ◽  
Fluent Software ◽  
Lift And Drag ◽  
Drag Ratio ◽  
Lift To Drag Ratio

Abstract The NACA4415 airfoil was numerically simulated with the help of the Fluent software to analyze its aerodynamic characteristics. Results are acquired as follows: The calculation accuracy of Fluent software is much higher than that of XFOIL software; the calculation result of SST k-ω(sstkw) turbulence model is closest to the experimental value; within a certain range, the larger the Reynolds number is, the larger the lift coefficient and lift-to-drag ratio of the airfoil will be, and the smaller the drag coefficient will be; when the angle of attack is less than the optimal angle of attack, the Reynolds number has less influence on the lift-to-drag coefficient and the lift-to-drag ratio; as the Reynolds number increases, the optimal angle of attack increases slightly, and the applicable angle of attack range for high lift-to-drag ratios becomes smaller.

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