Uniform Suction Research Articles

Effect of uniform blowing or suction on hypersonic spatially developing turbulent boundary layers

Effect of uniform blowing or suction on hypersonic spatially developing turbulent boundary layers

Effect of wall suction on rotating disk absolute instability

This research investigates the effect of uniform suction on the absolute instability of Type I cross-flow modes in the boundary layer on a rotating disk. Specifically, it is designed to investigate whether wall suction would transform the absolute instability into a global mode, as first postulated in the numerical simulations of Davies & Carpenter (J. Fluid Mech., vol. 486, 2003, pp. 287–329). The disk is designed so that with a suction parameter of $0.2$, the radial location of the absolute instability critical Reynolds number, $Re_{c_{A}}=650$, occurs on the disk. Wall suction is applied from $Re=317$ to 696.5. The design for wall suction follows that of Gregory & Walker (J. Fluid Mech., 1960, pp. 225–234) where an array of holes through the disk communicate between the measurement side of the disk and the underside of the disk which is inside of an enclosure that is maintained at a slight vacuum. The enclosure pressure is adjustable so that a range of suction or blowing parameters can be investigated. The holes in the measurement surface are covered by a compressed wire porous mesh to aid in uniformizing the suction on the measurement surface of the disk. The mesh is covered by a thin porous high-density polyethylene sheet featuring a $20~{\rm\mu}\text{m}$ pore size which provides a smooth finely porous surface. A companion numerical simulation is performed to investigate the effect that the size and vacuum pressure of the underside enclosure have on the uniformity of the measurement surface suction. Temporal disturbances are introduced using the method of Othman & Corke (J. Fluid Mech., 2006, pp. 63–94). The results document the evolution of disturbance wavepackets in space and time. These show a temporal growth of the wavepackets as the location of the absolute instability is approached which is in strong contrast to the temporal evolution without suction observed by Othman and Corke. The results appear to support the effect of wall suction on the absolute instability postulated by Thomas (PhD thesis, 2007, Cardiff University, UK) and Thomas & Davies (J. Fluid Mech., vol. 663, 2010, pp. 401–433).

圧力こう配を伴う乱流境界層における一様吹出し/吸込みの摩擦抵抗低減効果

Influences of pressure gradient on the friction drag reduction effect of uniform blowing or suction in a turbulent boundary layer is investigated by means of Reynolds-Averaged Navier-Stokes simulation. In the present study, to create an adverse-to-favorable pressure gradient, a suction-blowing velocity distribution is prescribed along the upper boundary. As a result, drag reduction effect of uniform blowing is increased by adverse pressure gradient and suppressed by favorable pressure gradient. On the other hand, it is also found that pressure gradient has a little influence on the overwall change in skin friction.

Friction drag reduction of a spatially developing boundary layer using a combined uniform suction and blowing

Friction drag reduction of a spatially developing boundary layer using a combined uniform suction and blowing

Implicit finite difference solution for the magneto-hydro-dynamic unsteady free convective flow and heat transfer of a third-grade fluid past a porous vertical plate

Magneto-hydro-dynamic (MHD) unsteady flow and heat transfer of a third grade fluid passing an infinite vertical porous plate with uniform suction applied at the plate has been studied. The governing nonlinear partial differential equations are reduced to a system of nonlinear algebraic equations using implicit finite difference schemes and then the system is solved using damped-Newton method. The effect of the various physical parameters on the velocity and temperature are studied. One of the important observations is that when the third order elastic parameter increases the velocity decreases, whereas an opposite effect is observed when second order elastic parameter increases. Present method is valid for all values of elastic parameters where as the earlier approximation methods like perturbation and power series methods are valid for small values of elastic parameter. Further the advantage of our method is that it does not require repeated derivation for every change in the boundary conditions.

Simulations of turbulent asymptotic suction boundary layers

ABSTRACTA series of large-eddy simulations of a turbulent asymptotic suction boundary layer (TASBL) was performed in a periodic domain, on which uniform suction was applied over a flat plate. Three Reynolds numbers (defined as ratio of free-stream and suction velocity) of Re = 333, 400 and 500 and a variety of domain sizes were considered in temporal simulations in order to investigate the turbulence statistics, the importance of the computational domain size, the arising flow structures as well as temporal development length required to achieve the asymptotic state. The effect of these two important parameters was assessed in terms of their influence on integral quantities, mean velocity, Reynolds stresses, higher order statistics, amplitude modulation and spectral maps. While the near-wall region up to the buffer region appears to scale irrespective of Re and domain size, the parameters of the logarithmic law (i.e. von Kármán and additive coefficient) decrease with increasing Re, while the wake strength decreases with increasing spanwise domain size and vanishes entirely once the spanwise domain size exceeds approximately two boundary-layer thicknesses irrespective of Re. The wake strength also reduces with increasing simulation time. The asymptotic state of the TASBL is characterised by surprisingly large friction Reynolds numbers and inherits features of wall turbulence at numerically high Re. Compared to a turbulent boundary layer (TBL) or a channel flow without suction, the components of the Reynolds-stress tensor are overall reduced, but exhibit a logarithmic increase with decreasing suction rates, i.e. increasing Re. At the same time, the anisotropy is increased compared to canonical wall-bounded flows without suction. The reduced amplitudes in turbulence quantities are discussed in light of the amplitude modulation due to the weakened larger outer structures. The inner peak in the spectral maps is shifted to higher wavelength and the strength of the outer peak is much less than for TBLs. An additional spatial simulation was performed, in order to relate the simulation results to wind tunnel experiments, which – in accordance with the results from the temporal simulation – indicate that a truly TASBL is practically impossible to realise in a wind tunnel. Our unique data set agrees qualitatively with existing literature results for both numerical and experimental studies, and at the same time sheds light on the fact why the asymptotic state could not be established in a wind tunnel experiment, viz. because experimental studies resemble our simulation results from too small simulation boxes or insufficient development times.

Non-Darcy unsteady MHD Hartmann flow in a porous medium with heat transfer

The time varying magneto-hydrodynamic (MHD) Hartmann non-Darcy flow with heat transfer through a porous medium of an electrically conducting, viscous, incompressible fluid between two infinite parallel insulating porous plates is studied. A non-Darcy model that obeys the Forchheimer extension is assumed for the characteristics of the porous medium. A uniform suction and injection as well as an externally applied uniform magnetic field are applied in the direction normal to the plates where a uniform and constant pressure gradient is imposed in the axial direction. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are considered in the energy equation. The effect of the magnetic field, the Hall current, the porosity of the medium, and the uniform suction and injection on both the velocity and temperature distributions are studied and interesting results are presented for various values of the existing parameters.

Homogeneous–heterogeneous reactions in stagnation point flow of Casson fluid due to a stretching/shrinking sheet with uniform suction and slip effects

Abstract This study deals with the effects of homogeneous–heterogeneous reaction on boundary layer flow of a non-Newtonian fluid near a stagnation point over a porous stretching/shrinking sheet with a constant suction. In this analysis Casson fluid is used to indicate the non-Newtonian fluid behavior by taking diffusion coefficients of both reactant and autocatalysis equal. The basic flow equations in form of partial differential equations are converted into a system of ordinary differential equations and then solved numerically. The influences of physical and fluid parameters on the velocity and concentration profiles are analyzed, presented and discussed through graphs. An increase in fluid velocity slip parameter reduces the magnitude of the velocity as well as increases the concentration in the boundary layer region. Furthermore, a unique solution is possible for all values of the stretching parameter (λ > 0), while in case of shrinking parameter (λ

Effects of ion slip and Hall current on unsteady Couette flow of a dusty fluid through porous media with heat transfer

In this study, the unsteady Couette flow with heat transfer of a dusty viscous incompressible electrically conducting fluid through a porous medium is studied with the consideration of both Hall current and ion slip. The parallel plates are porous and subjected to a uniform suction from above and injection from below while an external uniform magnetic field is applied perpendicular to the plates. A numerical solution for the governing momentum and energy equations are obtained using the finite difference method. The influence of magnetic field parameters, the porosity of the medium, suction or injection velocity, and ion slip parameter on velocity and temperature fields of both fluid and dust particles is demonstrated.

Investigation of heat transfer enhancement inside developing gravity-driven films along a vertical permeable plate subject to nonuniform suction

Flow and heat transfer through the boundary layers of a falling liquid film on a vertical permeable plate subject to nonuniform suction flow are analyzed in this work. The continuity, momentum, and energy equations are transformed to nonsimilar equations and solved using a validated implicit and iterative finite difference method. Increases in the Froude number, Galilei number, and the dimensionless average suction velocity are found to increase the skin friction coefficient, the Nusselt number, and the heat transfer enhancement ratios. These enhancement ratios are noticed to increase at the plate exit as the suction velocity power-law index increases. The Froude number for uniform suction case required to attain the same enhancement ratios due to nonuniform distribution of this suction flow is found to increase as the Galilei number, average suction velocity, and power-law index increase. It is found that the upper most values of the enhancement factors in heat transfer and Froude number are [Formula: see text] folds when the suction power-law index is equal to [Formula: see text]. This work demonstrated that significant heat transfer enhancement inside developing gravity-driven liquid films is attainable when properly distributing the suction velocity along the plate.

Effect of uniform blowing/suction in a turbulent boundary layer at moderate Reynolds number

A number of well-resolved large-eddy simulations (LES) of a spatially evolving turbulent boundary layer with uniform blowing or suction is performed in order to investigate the effect on skin friction drag as well as turbulence statistics and spectral composition at moderate Reynolds numbers up to Reθ=2500, based on the free-stream velocity and the momentum-loss thickness. The amplitude of uniform blowing or suction is set to be 0.1% of the free-stream velocity with different streamwise ranges of the controlled region.The boundary layer is thickened by blowing and thinned by suction. The Reynolds shear and normal stresses are increased by blowing and decreased by suction, most prominently, in the outer region. Through spectral analysis of the streamwise velocity and cross-spectra of the Reynolds shear stress, the enhancement and reduction of the fluctuation energy in the outer region by blowing and suction are found, respectively. It is also found that the emergence of a second peak in the outer region is promoted by blowing, while it is inhibited in the case of suction.In spite of the weak amplitude of the control, more than 10% of drag reduction and enhancement are achieved by means of blowing and suction, respectively. In the case of blowing, where drag reduction is achieved, the mean drag reduction rate increases as the blowing region extends because the local reduction rate, i.e.the streamwise gradient of the mean drag reduction rate, grows in the streamwise direction. The net-energy saving rate and the control gain have the same trends. It is found that a more effective skin friction drag reduction and control efficiency can be achieved with a wider control region that starts at a more upstream location.

The motion induced by the orthogonal stretching and shearing of a membrane beneath a quiescent fluid

The flow induced above an impermeable membrane undergoing orthogonal linear stretching and orthogonal linear shearing is investigated. For an exact solution of the Navier–Stokes equations, the orthogonal shearing motions must be related through the constant σ = γ δ, where γ and δ are the dimensionless streamwise and transverse shear rates, respectively. The resulting similarity reduction leads to three nonlinearly coupled ordinary differential equations governed by σ and the ratio of membrane stretch rates β. All possible solutions of these equations are found either numerically or, in special cases, analytically. Features of the σ = 0 solutions at β = 0 and asymptotically as β → ∞ are found to be in excellent agreement with numerical calculations. An aside calculation shows that orthogonal shearing in the absence of any plate stretching cannot exist. However, shearing in one coordinate direction is possible as long as the membrane stretches in at least one direction with the caveat that there exists uniform suction through a porous membrane.

Instabilities in the asymptotic suction boundary layer over a permeable, compliant wall

The spatial, linear stability of an incompressible parallel boundary layer flow with uniform suction through the wall is studied for the case of rigid and flexible bounding surfaces. It is demonstrated, first, that the effect of the plate’s permeability is crucial in defining the disturbance boundary conditions at the wall, and that stability limits depend strongly on it. Next, the combined effect of plate’s permeability and compliance on the onset of Tollmien-Schlichting modes is assessed. Finally, the possible insurgence of an absolute instability mode is studied, as function of the Reynolds number, the modulus of elasticity of the plate, and its permeability.

Stagnation-point flow of a hydromagnetic viscous fluid over stretching/shrinking sheet with generalized slip condition in the presence of homogeneous–heterogeneous reactions

An analysis is performed to study the effect of homogeneous–heterogeneous reactions on an electrically conducting viscous fluid near the stagnation-point past a permeable stretching/shrinking sheet with uniform suction and generalized slip condition. In this analysis we used the developed model of a homogeneous–heterogeneous reaction in boundary layer flow with equal diffusivities for reactant and autocatalysis. The governing partial differential equations in terms of continuity, momentum and concentration are transformed into ordinary differential equations and then solved numerically using shooting method. The results show that for the shrinking sheet, dual solutions exist in the certain range of involved parameters, while for stretching sheet, the solutions are unique. Comparison of the present results with previously published work is given and found in good agreement.

FINITE ELEMENT ANALYSIS OF UNSTEADY RADIATIVE MHD NATURAL CONVECTION COUETTE FLOW BETWEEN PERMEABLE PLATES WITH VISCOUS ND JOULE DISSIPATION

This paper discusses the unsteady magnetohydrodynamic free convection Couette flow of an incompressible viscous fluid between two infinite vertical permeable plates in the presence of thermal radiation with an exponentially decaying pressure gradient. A uniform magnetic field that is perpendicular to the plates, and uniform suction and injection through the plates are applied. The magnetic field lines are assumed to be fixed relative to the moving plate. The momentum equation takes buoyancy forces into consideration, while the energy equation considers thermal radiation effects and viscous and Joule dissipations. The fluid is considered to be a gray absorbing-emitting but nonscattering medium in the optically thick limit. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The coupled pair of non-linear partial differential equations is discretized using the Galerkin finite element method. This yields a system of non-linear algebraic equations which is solved using an iterative method to obtain the velocity and temperature distributions. The effects of suction parameter S, radiation parameter Rd, Received: May 15, 2014 c © 2015 Academic Publications, Ltd. url: www.acadpubl.eu Correspondence author 124 V.M. Job, S.R. Gunakala Grashof number Gr, magnetic parameter H, Prandtl number Pr and Eckert number Ec on the velocity and temperature distributions are investigated. AMS Subject Classification: 76R10, 76W05

Ion slip effect on unsteady Couette flow of a dusty fluid in the presence of uniform suction and injection with heat transfer

The combined effects of Hall current, ion slip, viscous dissipation, and Joule heating on unsteady magnetohydrodynamic Couette flow with heat transfer of a dusty viscous incompressible electrically conducting fluid are studied under a constant pressure gradient. The fluid is subjected to an external uniform magnetic field and a uniform suction and injection perpendicular to the plates (y-direction). Numerical solutions for the constitutive equations are obtained using the method of finite differences. The effects of the magnetic field, Hall parameter, and ion slip parameter on the velocity and temperature distributions for both the fluid and particle phases are investigated in details and shown graphically. It is found that, the Hall current and ion slip parameters have a great effect on the fluid and dust velocities and temperature.

Magneto hydrodynamic flow with viscous dissipation effects in the presence of suction and injection

Gyarmati's variational principle developed on the thermodynamic theory of irreversible pro- cesses is employed to study the viscous dissipation effects with uniform suction and injection on the infinite flat plate. The velocity and temperature fields inside the boundary layer are approximated as simple polynomial functions, and the functional of the variational principle is constructed. The Euler Lagrange equations are reduced to simple polynomial equations in terms of velocity and thermal boundary layer thicknesses. The velocity, temperature pro- files, skin friction and heat transfer with the viscous dissipation effects are analyzed and are compared with known numerical solutions. The comparison of the present solution with the existing solutions establishes the fact that the accuracy is remarkable. The prime objective of this investigation is to study the effects of viscous dissipation on the magneto hydrodynamic flow over a semi infinite flat plate with uniform suction and injection by using some recent developments in the field of thermodynamics of irreversible processes and to obtain numerical solution to the boundary layer flow and heat transfer with the help of a variational technique based on the governing principle of dissipative processes. According to the boundary layer theory, the irreversible processes of momentum and heat transfer in flows around bodies occur mainly inside a very thin layer adjacent to the surface of the body. Hence, it is quite appropriate to study these non equilibrium processes by a variational technique developed in the field of irreversible thermodynamics. The boundary layer flow of an incompressible electrically conducting fluid past a semi infinite flat plate in the presence of a transverse magnetic field has been studied recently by many rese- archers. The boundary layer solution for the magneto hydrodynamic flow over a semi infinite flat plate in the presence of transverse magnetic field was studied by Watanabe (1978, 1986) and Wa- tanabe and Pop (1994) by means of a difference-differential method. The analysis on stagnation point flow and asymmetric flow was investigated by Sparrow et al. (1963), Ariel (1994), Raptis (1991) and Chamkha (1998). Watanabe (1986) analyzed the magneto hydrodynamic boundary layer flow over a wedge and did not considered the energy equation. Hossain (1992) treated the viscous and Joule heating effects on magneto hydrodynamic free convection boundary layer flow with variable temperature on the plate. Watanabe and Pop (1993) solved the problem of ma- gneto hydrodynamic free convection flow over a wedge in the presence of a transverse magnetic field. Soundalgekar and Takhar (1977) considered the boundary layer equations for the aligned flow and temperature of an electrically conducting fluid past a semi infinite heated flat plate in the presence of a transverse magnetic field.

Heat transfer between two parallel porous plates for Couette flow under pressure gradient and Hall current

The aim of the present paper is to study the unsteady magneto-hydrodynamic viscous Couette flow with heat transfer in a Darcy porous medium between two infinite parallel porous plates considering Hall effect, and temperature dependent physical properties under constant pressure gradient. The parallel plates are assumed to be porous and subjected to a uniform suction from above and injection from below while the fluid is flowing through a porous medium that is assumed to obey Darcy’s law. A numerical solution for the governing nonlinear partial differential equations coupled with set of momentum equations and the energy equation including the viscous and Joule dissipations is adopted. The effect of the porosity of the medium, the Hall current and the temperature dependent viscosity and thermal conductivity on both the velocity and temperature distributions are investigated. It is found that the porosity number M has a marked effect on decreasing the velocity distribution (owing to a simultaneous increase in Darcy porous drag). Also the temperature T is decreased considerably with increasing porosity number. With increasing Hall current parameter m, the velocity component u (x-direction) is considerably increased, whereas velocity component w (z-direction) is reduced. Temperatures are decreased in the early stages of flow but effectively increased in the steady state with increasing m.

0620 壁面一様吹出し/吸込みの空間発達乱流境界層への影響

A series of large-eddy simulations of the spatially developing turbulent boundary layer with uniform blowing or suction at moderate Reynolds number, based on the free-stream velocity and the momentum thickness, up to Re_θ = 2500 are performed. Similarly to the previous work of the direct numerical simulation at low Reynolds number [Kametani & Fukagata, J. Fluid Mech., vol. 681, pp. 154-172, 2011], uniform blowing achieves the skin friction drag reduction and enhancement of the turbulence, while uniform suction has the opposite trends. In spite of blowing at 0.1% of free-stream velocity, around 18% of drag reduction is achieved. The root-mean-squares of turbulent uctuations and the spectral analysis show that blowing/suction affect the turbulence at the outer region notably. The distributions of the power-spectral density of streamwise velocity uctuation and the cross-spectra of the Reynolds shear stress are strongly distorted in the outer region. The decomposition of the skin friction drag indicates that blowing has potential to reduce skin friction drag despite it increases the turbulence even at moderate Reynolds numbers.

Numerical analysis of flow around porous rectangular cylinders with uniform injection or suction

The flow around rectangular cylinders of various aspect ratios of B/H = 2, 3 and 4 with uniform injection or suction through the rear and top/bottom surfaces has been studied numerically at a Reynolds number Re = 21,400. The effects of injection or suction through the cylinder surfaces have been linked to the analysis via the wall functions of the viscous sub–layer and log–law layer. The injection or suction has been characterised by an injection coefficient CQ = vw/u∞, which takes negative values for suction. The governing equations, which are a combination of the ensemble–averaged Navier–Stokes equations for incompressible flow in conjunction with the equations of a modified k–ε turbulence model, have been solved by the finite volume method. A non–uniform staggered grid arrangement has been used to economise on computing time. The results show that the vortex structure in the wake is influenced primarily by suction through the top and bottom surfaces of the rectangular cylinders. In addition, the parameters taken into account such as drag coefficient and Strouhal number are also affected by the injection coefficient as well as the injection/suction surfaces of the rectangular cylinders.