Flow separation

About: Flow separation is a research topic. Over the lifetime, 16708 publications have been published within this topic receiving 386926 citations.

Vorticity dynamics in an oscillatory flow over a rippled bed

Abstract: In the present paper we determine the oscillatory flow generated by surface gravity waves near a sea bottom covered with large-amplitude ripples. The vorticity equation and Poisson equation for the stream function are solved by means of a numerical approach based on spectral methods and finite-difference approximations. In order to test the numerical algorithm and in particular the numerical scheme used to generate vorticity along the ripple profile, we also perform an asymptotic analysis, which holds as the time t tends to zero. The main features of the time development of vorticity are analysed and particular attention is paid to the dynamics of the large vortices generated by flow separation at the ripple crests and along the ripple profile. Some of the results obtained by Longuet-Higgins (1981) are recovered; in particular, the present results show a vortex pair shed from the ripple crest every half-cycle. The determination of flow separation along the ripple profile induced by the pressure gradient and the inclusion of viscous effects allows us to obtain accurate quantitative results and detect some important phenomena never observed before.In particular it is shown that: (i) Whenever a vortex structure moves towards the bottom, a secondary vortex is generated near the ripple profile, which interacts with the primary vortex and causes it to move away from the bottom, (ii) Depending on the values of the parameters, the time development of the free shear layer shed from the ripple crest may produce two or even more vortex structures, (iii) Occasionally vortices generated previously may coalesce with the free shear layer shed from the ripple crest, generating a unique vortex structure.

Large Eddy Simulation of Turbulent Flow Through Submerged Vegetation

Abstract: Large Eddy Simulations (LES) are performed for an open channel flow through idealized submerged vegetation with a water depth (h) to plant height (hp) ratio of h/hp = 1.5 according to the experimental configuration of Liu et al. (J Geophys Res Earth Sci, 2008). They used a 1D laser Doppler velocimeter (LDV) to measure longitudinal and vertical velocities as well as turbulence intensities along several verticals in the flow and the data are used for the validation of the present simulations. The code MGLET is used to solve the filtered Navier–Stokes equations on a Cartesian non-uniform grid. In order to represent solid objects in the flow, the immersed boundary method is employed. The computational domain is idealized with a box containing 16 submerged circular cylinders and periodic boundary conditions are applied in both longitudinal and transverse directions. The predicted streamwise as well as vertical mean velocities are in good agreement with the LDV measurements. Furthermore, fairly good agreement is found between calculated and measured streamwise and vertical turbulence intensities. Large-scale flow structures of different shapes are present in the form of vortex rolls above the vegetation tops as well as locally generated trailing and von- Karman-type vortices due to flow separation at the free end and the sides of the cylinders. In this paper, the flow field is analyzed statistically and evidence is provided for the existence of these structures based on the LES.

Engineering fluid mechanics

Abstract: Introduction Preface 1. Fundamentals in Continuum Mechanics 1.1 Dynamics of fluid motion 1.2 Dynamics in rotating reference frame 1.3 Material objectivity and convective derivatives 1.4 Displacement gradient and relative strain 1.5 Reynold's transport theorem 1.6 Forces on volume element Exercise Problems Bibliography Nomenclature for chapter 1 2. Conservation equations in continuum mechanics 2.1 Mass conservation 2.2 Linear momentum conservation 2.3 Angular momentum conservation 2.4 Energy conservation 2.5 Thermodynamic relations Exercise Problems Bibliography Nomenclature for chapter 2 3. Fundamental Treatment for Fluid Engineering 3.1 Fluid static 3.1 Fluid-fluid interfaces Exercise Problems Bibliography Nomenclature for chapter 3 4. Perfect flow 4.1 Potential and inviscid flows Exercise Problems 4.2 General theories of turbomachinery 4.2.1 Moment of momentum theory 4.2.2 Airfoil theory 4.2.3 Efficiency and similarity rules of turbomachinery 4.2.4 Cavitation Exercise Problems Bibliography Nomenclature for chapter 4 5. Compressible flow 5.1 Speed of sound and Mach number 5.2 Isoentropic flow 5.3 Fanno and Reyleigh lines 5.4 Normal shock waves 5.5 Oblique shock wave Exercise Problems Bibliography Nomenclature for chapter 5 6. Newtonian flow 6.1 Navier-Stokes Equation Problems 6.2 Similitude and Nondimensionalization Exercise Problems 6.3 Basic flows derived from Navier-Stokes equation 6.3.1 Unidirectional flow in a gap space 6.3.2 Lubrication theory 6.3.3 Flow around sphere Problems 6.4 Flow through pipe 6.4.1 Entrance flow 6.4.2 Fully developed flow pipe 6.4.3 Transient Hagen-Poiseuille flow in pipe Exercise Problems 6.5 Laminar boundary layer theory 6.5.1 Flow over a flat plate 6.5.2 Integral Analysis of Boundary Layer equation 6.5.3 Boundary layer separation 6.5.4 Integral relation for thermal energy Exercise Problems 6.6Turbulent flow 6.6.1 Turbulence models 6.6.2 Turbulence heat transfer Exercise Problems Bibliography Nomenclature for chapter 6 7. Non-Newtonian fluid and flow 7.1 Non-Newtonian fluid and generalized Newtonian fluid flow 7.1.1 Rheological classifications 7.1.2 Generalized Newtonian fluid flow Exercise Problems 7.2 Standard flow and material functions 7.2.1 Simple shear flow 7.2.2 Shearfree flow 7.2.3 Oscillatory rheometric flow 7.2.4 Viscometric flow in rheomery Exercise Problems 7.3 Viscoelastic fluid and flow 7.3.1 Linear viscoelastic rheological equation 7.3.2 Linear and nonlinear viscoelastic models 7.3.3 Viscoelastic models to standard flow and application to some engineering flow problems 7.3.3.1 UCM, CRM and Giesekus equation 7.3.3.2 Unidirectional basic flow problems Exercise Problems Bibliography Nomenclature for chapter 7 8. Magnetic fluid and flow 8.1 Thermophysical properties Exercise Problems 8.2 Ferrohydrodynamics equation Exercise Problems 8.3 Basic flows and applications 8.3.1 Generalized Bernoulli equation 8.3.2 Hydrostatics 8.3.3 Thermoconvective phenomena Exercise Problems Bibliography Nomenclature for chapter 8

Flow Structure on a Delta Wing of Low Sweep Angle

Abstract: The instantaneous and averaged flow structure past a delta wing of low sweep angle is investigated using a technique of high-image-density particle image velocimetry. Emphasis is on crossflow planes, where vortex breakdown and stall occur, and the identification of buffeting mechanisms in these regions. At all values of angle of attack up to the fully stalled condition, the averaged vorticity layer exhibits an elongated form; the classical (single) large-scale concentration of vorticity within the leading-edge vortex of a highly swept wing is not present. At low angle of attack α, this elongated, averaged layer can exhibit, however, well-defined concentrations of vorticity. These elongated vorticity layers are accompanied by narrow recirculation zones adjacent to the wing surface. Furthermore, the averaged streamline topology exhibits, at lower α, a saddle point located slightly outboard of the leading edge, in contrast to a saddle point located on the plane of the symmetry of a highly swept wing. Patterns of velocity fluctuation and Reynolds stress show peaks that are generally coincident with large values of averaged vorticity, which indicates that they arise from unsteady events in regions of high shear