scholarly journals A model of an inflatable elastic aerofoil

2021 ◽  
Vol 131 (1) ◽  
Author(s):  
A. A. Yorkston ◽  
M. G. Blyth ◽  
E. I. Părău
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Aerodynamic Characteristics ◽  
Flow Speed ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Inviscid Fluid ◽  
Viscous Boundary Layer ◽  
Aerodynamic Shape ◽  
Internal Support

AbstractA novel method is presented to calculate the deformation of a simple elastic aerofoil with a view to determining its aerodynamic viability. The aerofoil is modelled as a thin two-dimensional elastic sheet whose ends are joined together to form a corner of prescribed angle, with a simple support included to constrain the shape to resemble that of a classical aerofoil. The weight of the aerofoil is counterbalanced exactly by the lift force due to a circulation set according to the Kutta condition. An iterative process based on a boundary integral method is used to compute the deformation of the aerofoil in response to an inviscid fluid flow, and a range of flow speeds is determined for which the aerofoil maintains an aerodynamic shape. As the flow speed is increased the aerofoil deforms significantly around its trailing edge, resulting in a negative camber and a loss of lift. The loss of lift is ameliorated by increasing the inflation pressure but at the expense of an increase in drag as the aerofoil bulges into a less aerodynamic shape. Boundary layer calculations and nonlinear unsteady viscous simulations are used to analyse the aerodynamic characteristics of the deformed aerofoil in a viscous flow. By tailoring the internal support the viscous boundary layer separation can be delayed and the lift-to-drag ratio of the aerofoil can be substantially increased.

Gas bubbles bursting at a free surface

1993 ◽  
Vol 254 ◽  
pp. 437-466 ◽  
Author(s):  
J. M. Boulton-Stone ◽  
J. R. Blake
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
High Speed ◽  
Boundary Layer Separation ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Viscous Effects ◽  
Animal Cells ◽  
Jet Formation ◽  
Jet Breakup

When a small air bubble bursts from an equilibrium position at an air/water interface, a complex motion ensues resulting in the production of a high-speed liquid jet. This free-surface motion following the burst is modelled numerically using a boundary integral method. Jet formation and liquid entrainment rates from jet breakup into drops are calculated and compared with existing experimental evidence. In order to investigate viscous effects, a boundary layer is included in the calculations by employing a time-stepping technique which allows the boundary mesh to remain orthogonal to the surface. This allows an approximation of the vorticity development in the region of boundary-layer separation during jet formation. Calculated values of pressure and energy dissipation rates in the fluid indicate a violent motion, particularly for smaller bubbles. This has important implications for the biological industry where animal cells in bioreactors have been found to be killed by the presence of small bubbles.

Prospects of Studies in Region of Low-Sized Aircraft (Review)

2014 ◽  
Vol 9 (2) ◽  
pp. 95-115
Author(s):  
Ilya Zverkov ◽  
Alexey Kryukov ◽  
Genrich Grek
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layer Separation ◽  
Aerodynamic Characteristics ◽  
Point Of View ◽  
Wavy Surface ◽  
Local Boundary ◽  
Effective Operation ◽  
Forward Edge ◽  
The Given

In the given review the problem of improvement of aerodynamic characteristics of the low-sized aircraft is considered with point of view of the fundamental phenomena of the mechanics of liquid, gas and plasma. It is a problem of the local boundary layer separation (separated bubbles) and flow separation from a wing forward edge at which all global structure of a flow varies. The review of the works establishing this interrelation and methods of the influence, eliminating harmful consequences of the separations is submitted. The method of separation elimination with help of a wavy surface, as the most perspective and easily sold on practice is in more details allocated in this review. The second part of the review is devoted to the analysis of a flow of elements of designs of various low-sized aircraft with indication of probably problem places where the flow is realized at Reynolds number less than 106 and where can arise the local separations. Application of a wavy surface in such places can improve aerodynamic characteristics of the flying device promoting its more effective operation

Role of Shock and Boundary Layer Separation on Unsteady Aerodynamic Characteristics of Oscillating Transonic Cascade

2003 ◽  
Author(s):  
Mizuho Aotsuka ◽  
Toshinori Watanabe ◽  
Yasuo Machina
Keyword(s):  
Boundary Layer ◽  
Pressure Fluctuations ◽  
Boundary Layer Separation ◽  
Aerodynamic Characteristics ◽  
Compressor Cascade ◽  
Layer Interaction ◽  
Unsteady Aerodynamic ◽  
Shock Boundary Layer Interaction ◽  
Boundary Layer Interaction ◽  
Shock Oscillation

The unsteady aerodynamic characteristics of an oscillating compressor cascade composed of Double-Circular-Arc airfoil blades were both experimentally and numerically studied under transonic flow conditions. The study aimed at clarifying the role of shock waves and boundary layer separation due to the shock boundary layer interaction on the vibration characteristics of the blades. The measurement of the unsteady aerodynamic moment on the blades was conducted in a transonic linear cascade tunnel using an influence coefficient method. The cascade was composed of seven DCA blades, the central one of which was an oscillating blade in a pitching mode. The unsteady moment was measured on the central blade as well as the two neighboring blades. The behavior of the shock waves was visualized through a schlieren technique. A quasi-three dimensional Navier-Stokes code was developed for the present numerical simulation of the unsteady flow fields around the oscillating blades. A k-ε turbulence model was utilized to adequately simulate the flow separation phenomena caused by the shock-boundary layer interaction. The experimental and numerical results complemented each other and enabled a detailed understanding of the unsteady aerodynamic behavior of the cascade. It was found that the surface pressure fluctuations induced by the shock oscillation were the governing factor for the unsteady aerodynamic moment acting on the blades. Such pressure fluctuations were primarily induced by the movement of impingement point of the shock on the blade surface. During the shock oscillation the separated region caused by the shock boundary layer interaction also oscillated along the blade surface, and induced additional pressure fluctuations. The shock oscillation and the movement of the separated region were found to play the principal role in the unsteady aerodynamic and vibration characteristics of the transonic compressor cascade.

Mass transport in the bottom boundary layer of cnoidal waves

1976 ◽  
Vol 74 (3) ◽  
pp. 401-413 ◽  
Author(s):  
M. De St Q. Isaacson
Keyword(s):  
Boundary Layer ◽  
Mass Transport ◽  
Wave Theory ◽  
Bottom Boundary Layer ◽  
Inviscid Fluid ◽  
Viscous Boundary Layer ◽  
Cnoidal Waves ◽  
Bottom Boundary ◽  
Transport Velocity ◽  
Mass Transport Velocity

This study deals with the mass-transport velocity within the bottom boundary layer of cnoidal waves progressing over a smooth horizontal bed. Mass-transport velocity distributions through the boundary layer are derived and compared with that predicted by Longuet-Higgins (1953) for sinusoidal waves. The mass transport at the outer edge of the boundary layer is compared with various theoretical results for an inviscid fluid based on cnoidal wave theory and also with previous experimental results. The effect of the viscous boundary layer is to establish uniquely the bottom mass transport and this is appreciably greater than the somewhat arbitrary prediction for an inviscid fluid.

Boundary-Integral Computation of Hydrodynamic Interactions Between a Three-Dimensional Body and an Infinitely Long Cylinder

1993 ◽  
Vol 37 (04) ◽  
pp. 281-297
Author(s):  
Zhi Guo ◽  
Allen T. Chwang
Keyword(s):  
Circular Cylinder ◽  
Numerical Technique ◽  
Three Dimensional ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Hydrodynamic Interactions ◽  
Inviscid Fluid ◽  
Body Of Revolution ◽  
Infinite Region ◽  
Added Masses

Hydrodynamic interactions between a three-dimensional body of revolution and an infinitely long circular cylinder in an inviscid fluid are studied numerically by the boundary-integral method. The added-mass coefficients and their derivatives are computed in terms of the solutions of four integral equations of the second kind. A numerical technique based on variable transformations is developed to evaluate integrations over steep peaks. Integrations over the cylindrical surface are properly computed by mapping the infinite region onto a finite region and regularizing the ill-behaved kernels with sharp peaks. The discrete added masses and their derivatives are fitted by the least-squares approximation on the basis of Legendre polynomials. As a practical example, the moving trajectories of a sphere conveyed by a uniform flow around a fixed circular cylinder are computed and presented.

Surface-tension effects in the contact of liquid surfaces

1989 ◽  
Vol 203 ◽  
pp. 149-171 ◽  
Author(s):  
Hasan N. Oguz ◽  
Andrea Prosperetti
Keyword(s):  
Surface Tension ◽  
Experimental Evidence ◽  
Integral Method ◽  
Model Problem ◽  
Mathematical Formulation ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Inviscid Fluid ◽  
Condensation Nuclei ◽  
Rain Drops

The process by which two surfaces of the same liquid establish contact, as when two drops collide or raindrops fall on water, is studied. The mathematical formulation is based on the assumption of an incompressible, inviscid fluid with surface tension. A model problem with a simplified geometry is solved numerically by means of a boundary-integral method. The results imply that a number of toroidal bubbles form and remain entrapped between the contacting surfaces. Experimental evidence for this process, which is important for boiling nucleation and the formation of condensation nuclei for rain drops, is found in the literature.

The boundary layer separation from streamlined surfaces and new ways of its prevention in diffusers

2017 ◽  
Author(s):  
Arkady Zaryankin ◽  
Andrey Rogalev ◽  
Ivan Komarov ◽  
V. Kindra ◽  
S. Osipov
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Layer Separation

scholarly journals Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil

2021 ◽  
Vol 11 (6) ◽  
pp. 2593
Author(s):  
Yasir Al-Okbi ◽  
Tze Pei Chong ◽  
Oksana Stalnov
Keyword(s):  
Boundary Layer ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Shear Instability ◽  
Vortical Flow ◽  
High Angle ◽  
High Angle Of Attack ◽  
Layer Separation ◽  
Aerodynamic Performances

Leading edge serration is now a well-established and effective passive control device for the reduction of turbulence–leading edge interaction noise, and for the suppression of boundary layer separation at high angle of attack. It is envisaged that leading edge blowing could produce the same mechanisms as those produced by a serrated leading edge to enhance the aeroacoustics and aerodynamic performances of aerofoil. Aeroacoustically, injection of mass airflow from the leading edge (against the incoming turbulent flow) can be an effective mechanism to decrease the turbulence intensity, and/or alter the stagnation point. According to classical theory on the aerofoil leading edge noise, there is a potential for the leading edge blowing to reduce the level of turbulence–leading edge interaction noise radiation. Aerodynamically, after the mixing between the injected air and the incoming flow, a shear instability is likely to be triggered owing to the different flow directions. The resulting vortical flow will then propagate along the main flow direction across the aerofoil surface. These vortical flows generated indirectly owing to the leading edge blowing could also be effective to mitigate boundary layer separation at high angle of attack. The objectives of this paper are to validate these hypotheses, and combine the serration and blowing together on the leading edge to harvest further improvement on the aeroacoustics and aerodynamic performances. Results presented in this paper strongly indicate that leading edge blowing, which is an active flow control method, can indeed mimic and even enhance the bio-inspired leading edge serration effectively.

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