Numerical Study of Unsteady Flow Around Airfoil With Spoiler

1998 ◽  
Vol 65 (1) ◽  
pp. 164-170 ◽  
Author(s):  
Cheng Xu ◽  
W. W. H. Yeung
Keyword(s):  
Numerical Study ◽  
Piecewise Linear ◽  
Separated Flow ◽  
Vortex Sheet ◽  
Time Step ◽  
Discrete Vortex ◽  
Vortex Model ◽  
Bernoulli’S Equation ◽  
Pressure Distributions ◽  
Rapid Deployment

A discrete vortex model based on the panel method has been developed to simulate the two-dimensional unsteady separated flow generated by the rapid deployment of a spoiler on the upper surface of an airfoil. This method represents the boundary surfaces by distributing piecewise linear-vortex and constant source singularities on discrete panels. The wake of the spoiler and airfoil is represented by discrete vortices. At each sharp edge, a vortex sheet is used to feed discrete vortices at every time-step to form the downstream wake. The length and strength of each shed vortex sheet are determined by the continuity equation and a condition such that the flow, the net force, and the pressure difference across the vortex sheet are zero. The flow patterns behind the spoiler at different time-steps are presented. The pressure distributions on the airfoil based on the unsteady Bernoulli’s equation are compared, where possible, with the experimental results and other computational results. The adverse lift effects have been obtained, and similar effects have been measured in experiments.

A numerical study of vortex interaction

1984 ◽  
Vol 146 ◽  
pp. 331-345 ◽  
Author(s):  
I. G. Bromilow ◽  
R. R. Clements
Keyword(s):  
Flow Visualization ◽  
Numerical Study ◽  
Experimental Studies ◽  
Shear Layers ◽  
Controlled Study ◽  
Vortex Interaction ◽  
Flow Conditions ◽  
Discrete Vortex ◽  
Vortex Model ◽  
Discrete Vortex Model

Flow visualization has shown that the interaction of line vortices is a combination of tearing, elongation and rotation, the extent of each depending upon the flow conditions. A discrete-vortex model is used to study the interaction of two and three growing line vortices of different strengths and to assess the suitability of the method for such simulation.Many of the features observed in experimental studies of shear layers are reproduced. The controlled study shows the importance and rapidity of the tearing process under certain conditions.

Discrete Vortex Simulation of Pulsating Flow Behind a Normal Plate

1994 ◽  
Vol 116 (4) ◽  
pp. 862-869 ◽  
Author(s):  
Hyung Jin Sung ◽  
Young Nam Kim ◽  
Jae Min Hyun
Keyword(s):  
Numerical Study ◽  
Flow Characteristics ◽  
Separated Flow ◽  
Vortex Method ◽  
Threshold Value ◽  
Numerical Results ◽  
Pulsation Frequency ◽  
Discrete Vortex ◽  
Freestream Velocity ◽  
Variable Position

A numerical study is made of the separated flow behind a flat plate. The plate is placed normal to the direction of the approach flow. The oncoming freestream velocity contains a pulsating part, U∞ = U0(1 + A0cosfpt). The temporal behavior of vortex shedding patterns is scrutinized over broad ranges of the two externally specified parameters, i.e., the pulsation amplitude (A0≤ 0.6), and the dimensionless pulsation frequency, (fp≤0.32). A version of the discrete vortex method is utilized. The variable-position nascent vortex technique is applied, and it proves to be adequate for pulsating approach flows. The numerical results clearly capture the existence of lock-on when fp exceeds a threshold value. The modulation of vorticity shedding is also detected when fp is reasonably low. The influence of A0 on the flow characteristics is examined in detail. As A0 increases to a moderate value (e.g., A0≤0.6), an appreciable broadening is seen of the range of fp for which lock-on occurs. Based on the numerical results, three characteristic flow modes in the wakes are identified. These findings are qualitatively consistent with the existing flow-visualization studies for a cylinder.

scholarly journals Conformal Mapping-Based Discrete Vortex Method for Simulating 2-D Flows around Arbitrary Cylinders

2021 ◽  
Vol 9 (12) ◽  
pp. 1409
Author(s):  
Guoqing Jin ◽  
Zhe Sun ◽  
Zhi Zong ◽  
Li Zou ◽  
Yingjie Hu
Keyword(s):  
Conformal Mapping ◽  
Vortex Method ◽  
Reynolds Numbers ◽  
Mapping Method ◽  
Mirror Image ◽  
The Body ◽  
Time Step ◽  
Discrete Vortex ◽  
Fluid Field ◽  
Pressure Distributions

A novel technique based on conformal mapping and the circle theorem has been developed to tackle the boundary penetration issue, in which vortex blobs leak into structures in two-dimensional discrete vortex simulations, as an alternative to the traditional method in which the blobs crossing the boundary are simply removed from the fluid field or reflected back to their mirror-image positions outside the structure. The present algorithm introduces an identical vortex blob outside the body using the mapping method to avoid circulation loss caused by the vortex blob penetrating the body. This can keep the body surface streamlined and guarantees that the total circulation will be constant at any time step. The model was validated using cases of viscous incompressible flow passing elliptic cylinders with various thickness-to-chord ratios at Reynolds numbers greater than Re = 1 × 105. The force and velocity fields revealed that this boundary scheme converged, and the resultant time-averaged surface pressure distributions were all in excellent agreement with wind tunnel tests. Furthermore, a flow around a symmetrical Joukowski foil at Reynolds number Re = 4.62 × 104, without considering the trailing cusp, was investigated, and a close agreement with the experimental data was obtained.

An Experimental and Theoretical Investigation of the Structure of a Trailing Vortex Wake

1977 ◽  
Vol 28 (1) ◽  
pp. 39-50 ◽  
Author(s):  
R G Sampson
Keyword(s):  
Significant Proportion ◽  
Vortex Sheet ◽  
Transverse Plane ◽  
Tip Vortex ◽  
Turbulent Vortex ◽  
Vortex Model ◽  
Vorticity Distribution ◽  
Pressure Distributions ◽  
Improved Technique ◽  
Good Agreement

SummaryAn improved technique for the use of a five-hole yaw probe has been used in determining velocity, vorticity and pressure distributions over a transverse plane five chords downstream of a lifting wing. A well-defined tip vortex is shown to exist, together with a vortex sheet which contains a significant proportion of the total vorticity. The vorticity distribution is compared with that predicted by the calculation of vortex sheet roll-up using a two-dimensional array of line vortices. Good agreement is obtained, and the validity of using time steps large enough to inhibit the chaotic motion found in some calculations of this type is demonstrated. The structure of the tip vortex is found to be well described by the turbulent vortex model of Hoffman and Joubert.

Computational Methods With Vortices—The 1988 Freeman Scholar Lecture

1989 ◽  
Vol 111 (1) ◽  
pp. 5-52 ◽  
Author(s):  
Turgut Sarpkaya
Keyword(s):  
Computational Methods ◽  
Evolution Equations ◽  
Operator Splitting ◽  
Three Dimensional ◽  
Separated Flow ◽  
Body Representation ◽  
Vortex Sheet ◽  
Personal View ◽  
Discrete Vortex ◽  
Practical Applications

A comprehensive review is presented of the computational methods based upon Helmholtz’s powerful concepts of vortex dynamics, making use of Lagrangian or mixed Lagrangian-Eulerian schemes, the Biot-Savart law or the Vortex-in-Cell methods. The ingenious approximations and smoothing schemes developed in search of predictive models, qualitative solutions, new insights, or just some inspiration in the simulation of often two-dimensional, occasionally three-dimensional, and almost always incompressible fluids are described in detail. One is forewarned at the onset that chaos awaits at the end of the road. The challenge is to produce results in the face of ever accumulating errors within a time scale appropriate for the investigation. The review is organized around two major sections: Theoretical foundations and practical applications of vortex methods. The first covers topics such as vorticity and laws of transportation, evolution equations for a vortex sheet, real vortices and instabilities, Biot-Savart law, smoothing techniques (cutoff schemes, amalgamation of vortices, subvortex methods), cloud-in-cell or vortex-in-cell methods, body representation (Routh’s rule, surface singularity distributions), operator splitting and the random walk method (description and convergence), and asymmetry introduction. The next section covers contra flowing streams, vortical flows in aerodynamics (vortex sheet roll-up; slender-body, two-vortex, multi-discrete vortex, and segment or panel methods; three-dimensional flow models, and vortex-lattice methods), separated flow about cylindrical bodies (circular cylinder, sharp-edged bodies, arbitrarily-shaped bodies), general three-dimensional flows (vortex rings, turbulent spots, temporally and spatially-growing shear layers, and other applications (vortex-blade interactions, combustion phenomena, acoustics, contour dynamics, interaction of line vortices, chaos, and turbulence). The review is concluded with a brief comparison of these methods with others used in computational fluid dynamics and a personal view of their future prospects.

NAM Application for Simulation of Unsteady Separation Flow around Airfoil with Spoiler

2014 ◽  
Vol 598 ◽  
pp. 156-159
Author(s):  
Vladimir A. Frolov ◽  
Ksenia V. Redkina ◽  
Liu He
Keyword(s):  
Complex Variable ◽  
Separated Flow ◽  
Vortex Sheet ◽  
Separation Flow ◽  
Time Step ◽  
Unsteady Separation ◽  
Numerical Analytical Method ◽  
Modeling Behavior ◽  
Separation Zones ◽  
Unsteady Separated Flow

A Numerical-Analytical Method (NAM) and Discrete Vortices Method (DVM) are developed for simulating unsteady separated flow around an airfoil with a spoiler. For flow separated at each sharp edge, such as the spoiler tips and the trailing edge of the airfoil, a vortex sheet is used to feed discrete vortices at each time step. The solution is determined under the assumption of fluid being ideal and incompressible. This paper develops modeling behavior of the vortices around the airfoil with the spoiler. The NAM based into the combination of the DVM and TFCV (Theory Function of Complex Variable) that gives to increase the accuracy of the calculation. In this paper the variation of the separation zones for the unsteady separated flow are shown.

A Numerical Study of Oblique Water Entry Problems

2020 ◽  
Author(s):  
Yanni Chang ◽  
Albert Y. Tong
Keyword(s):  
Circular Cylinder ◽  
Transient Flow ◽  
Numerical Study ◽  
Piecewise Linear ◽  
Three Dimensional ◽  
Water Entry ◽  
Air Entrapment ◽  
Pressure Distributions ◽  
Parametric Studies ◽  
Inclined Angle

Abstract A series of numerical experiments have been carried out on the water entry problem of three-dimensional multi-degree-freedom cylinders. The circular cylinder was released above the water with a specified inclined angle and velocity at entry. The hydrodynamics of the water entry problem have been investigated numerically. The Piecewise Linear Interface Calculation (PLIC) schemes have been applied in conjunction with the Volume of Fluid (VOF) method to capture the interface. Overset meshes have been adopted to handle the moving object. The numerical model is built on the framework of OpenFOAM which is an open-source C++ toolbox. Numerical results have been obtained. Transient flow and pressure distributions have been generated. The presence of air entrapment which has been reported experimentally has also been confirmed in the numerical solution. The fluid physics of the oblique water entry problem such as the formation and development of the air entrapment has been explored. The transient positions and inclined angles of the moving circular cylinder have been found to be in good agreement with the experimental results. Parametric studies have been performed with major findings reported.

Separated Flow Past a Slender Delta Wing at Incidence

1973 ◽  
Vol 24 (2) ◽  
pp. 120-128 ◽  
Author(s):  
J E Barsby
Keyword(s):  
Delta Wing ◽  
Separated Flow ◽  
Leading Edge ◽  
Vortex Sheet ◽  
Simultaneous Equations ◽  
Delta Wings ◽  
Nested Iteration ◽  
Finite Difference Technique ◽  
Flow Past ◽  
Vortex Systems

SummarySolutions to the problem of separated flow past slender delta wings for moderate values of a suitably defined incidence parameter have been calculated by Smith, using a vortex sheet model. By increasing the accuracy of the finite-difference technique, and by replacing Smith’s original nested iteration procedure, to solve the non-linear simultaneous equations that arise, by a Newton’s method, it is possible to extend the range of the incidence parameter over which solutions can be obtained. Furthermore for sufficiently small values of the incidence parameter, new and unexpected results in the form of vortex systems that originate inboard from the leading edge have been discovered. These new solutions are the only solutions, to the author’s knowledge, of a vortex sheet leaving a smooth surface.Interest has centred upon the shape of the finite vortex sheet, the position of the isolated vortex, and the lift, and variations of these quantities are shown as functions of the incidence parameter. Although no experimental evidence is available, comparisons are made with the simpler Brown and Michael model in which all the vorticity is assumed to be concentrated onto an isolated line vortex. Agreement between these two models becomes very close as the value of the incidence parameter is reduced.

A numerical study of the descent of a vortex pair in a stably stratified atmosphere

1975 ◽  
Vol 71 (1) ◽  
pp. 1-13 ◽  
Author(s):  
F. M. Hill
Keyword(s):  
Numerical Methods ◽  
Numerical Study ◽  
Vortex Pair ◽  
Vortex Sheet ◽  
Discrete Line

Numerical methods are used to investigate the motion of a horizontal vortex pair through a stably stratified atmosphere. The vortices carry with them a mass of fluid whose density differs from that of the air through which it descends, and the surface of this accompanying fluid becomes a vortex sheet, which is modelled by a set of discrete line vortices.It is shown that, at first, the vortex pair slows down with the shape of the envelope of the accompanying fluid remaining constant. Later, vorticity concentrates at the rear, initiating detrainment and causing a downward acceleration of the vortex pair. Throughout the motion, the vortices approach each other.

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