A DNS study on the effects of convex streamwise curvature on coherent structures in a temporally-developing turbulent boundary layer with supercritical water

Dave, Nikunj; Azih, Chukwudi; Yaras, M. I.

doi:10.1016/j.ijheatfluidflow.2013.09.003

Cited by 15 publications

(6 citation statements)

References 30 publications

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“…For each time step, the solution is declared as converged when the rms of the normalized residuals 45 of the governing equations is reduced to less than 10 5 , and this is realized with up to five outer-loop iterations per time step. With the same computational algorithm as that of the present study, the studies of Brinkerhoff and Yaras, 19 Dave et al, 48 and Reinink and Yaras 26 indicate that a satisfactory level of convergence is achieved with rms residuals less than 10 5 .…”

Section: E Governing Equations and The Solution Methodssupporting

confidence: 54%

Effects of spatial gradients in thermophysical properties on the topology of turbulence in heated channel flow of supercritical fluids

Azih

Yaras

2018

Physics of Fluids

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The current literature suggests that large spatial gradients of thermophysical properties, which occur in the vicinity of the pseudo-critical thermodynamic state, may result in significant variations in forced-convection heat transfer rates. Specifically, these property gradients induce inertia- and buoyancy-driven phenomena that may enhance or deteriorate the turbulence-dominated heat convection process. Through direct numerical simulations, the present study investigates the role of coherent flow structures in channel geometries for non-buoyant and buoyant flows of supercritical water, with buoyant configurations involving wall-normal oriented gravitational acceleration and downstream-oriented gravitational acceleration. This sequence of simulations enables the evaluation of the relative contributions of inertial and buoyancy phenomena to heat transfer variations. In these simulations, the state of the working fluid is in the vicinity of the pseudo-critical point. The uniform wall heat flux and the channel mass flux are specified such that the heat to mass flux ratio is 3 kJ/kg, with an inflow Reynolds number of 12 000 based on the channel hydraulic diameter, the area-averaged inflow velocity, and fluid properties evaluated at the bulk temperature and pressure of the inflow plane. In the absence of buoyancy forces, notable reductions in the density and viscosity in close proximity of the heated wall are observed to promote generation of small-scale vortices, with resultant breakdown into smaller scales as they interact with preexisting larger near-wall vortices. This interaction results in a reduction in the overall thermal mixing at particular wall-normal regions of the channel. Under the influence of wall-normal gravitational acceleration, the wall-normal density gradients are noted to enhance ejection motions due to baroclinic vorticity generation on the lower wall, thus providing additional wall-normal thermal mixing. Along the upper wall, the same mechanism generates streamwise vorticity of the opposing sense of rotation in the close vicinity to the respective legs of the hairpin vortices causing a net reduction in thermal mixing. Finally, in the case of downstream-oriented gravitational acceleration, baroclinic vorticity generation as per spanwise density gradients causes additional wall-normal thermal mixing by promoting larger-scale ejection and sweep motions.

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Section: E Governing Equations and The Solution Methodssupporting

confidence: 54%

Effects of spatial gradients in thermophysical properties on the topology of turbulence in heated channel flow of supercritical fluids

Azih

Yaras

2018

Physics of Fluids

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“…So & Mellor 1973;Ramaprian & Shivaprasad 1978, 1982Hoffmann, Muck & Bradshaw 1985; Barlow & Johnston 1988;Holloway & Tavoularis 1992;Holloway, Roach & Akbary 2005) and numerically (e.g. Moser & Moin 1987;Neves, Moin & Moser 1994;Kim & Rhode 2000;Blin, Hadjadj & Vervisch 2003;Dave, Azih & Yaras 2013) over the past decades, there exist substantially fewer studies of the flow in the boundary layer over liquid, propagating surface waves (e.g. Takeuchi, Leavitt & Chao 1977;Hsu, Hsu & Street 1981;Hsu & Hsu 1983;Sullivan, McWilliams & Moeng 2000;Yang & Shen 2010;Buckley & Veron 2016).…”

mentioning

confidence: 99%

Boundary layer formulations in orthogonal curvilinear coordinates for flow over wind-generated surface waves

Yousefi

Véron

2020

J. Fluid Mech.

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“…The results of the velocity profiles showed that the velocity decreases in the outer region of the boundary layer, while it increases near the wall. In another similar study carried out by Dave et al [5], the development of a STBL on a convex curvature is evaluated. The results of their study indicated the stabilizing impact of this modification by distributing the hairpin-like vertical flow in the TBL.…”

Section: Introductionmentioning

confidence: 99%

A numerical study over the effect of curvature and adverse pressure gradient on development of flow inside gas transmission pipelines

Yadegari

Khoshnevis

2020

J Braz. Soc. Mech. Sci. Eng.

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In order to inspect the effects of adverse pressure gradient (APG) and curvature on the corrosion in the main gas transmission pipelines, the mean velocity and turbulence boundary layer on the walls of six different geometries including a straight pipe (A), a convex pipe (B 1), a concave pipe (B 2), a convex diffuser (C 1), a concave diffuser (C 2) and a straight diffuser (D) are calculated. The values of pressure gradient and curvature parameters are chosen 0.62 and 0.023, respectively. The results indicate that the corrosion in the concave curvature is greater than that the corrosion in the convex curvature, since the turbulence intensity increases in the concave curvature while it is suppressed in the convex curvature. In addition, when the boundary layer is exposed to APG and concave curvature simultaneously, the corrosion is greater than the situation when there is only APG or concave curvature. Ultimately, it was found that for the six studied geometries, there are two flow regimes (for velocities lower than 36 m/s) that the turbulence quantities are dependent on velocity. However, for velocities more than 36 m/s, the turbulence quantities and other affected quantities in the shear region are independent. Keywords Curvature • Adverse pressure gradient (APG) • k − − SST turbulence model • Corrosion List of symbols A Flow in a straight pipe B Flow in a curved pipe B1 Flow in a curved pipe with boundary layer developing on the convex side B2 Flow in a curved pipe with boundary layer developing on the concave side C Flow in a curved diffuser C1 Flow in a curved diffuser with boundary layer developing on the convex side C2 Flow in a curved diffuser with boundary layer developing on the concave side D Flow in a straight diffuser H Shape factor K Turbulent kinetic energy per unit mass (m 2 /s 2) k r The inverse of curvature radius (m −1) p Pressure (kgm/s 2) * Boundary layer thickness (mm) Displacement thickness (mm) Dissipation rate of the turbulent kinetic energy per unit mass (m 2 /s 2) Momentum thickness (mm) Von Karman constant (= 0.41) t Kinematic eddy viscosity (m 2 /s) Kinematic viscosity (m 2 /s) Density (kg/m 3) Specific dissipation rate (1/s)

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A DNS study on the effects of convex streamwise curvature on coherent structures in a temporally-developing turbulent boundary layer with supercritical water

Cited by 15 publications

References 30 publications

Effects of spatial gradients in thermophysical properties on the topology of turbulence in heated channel flow of supercritical fluids

Effects of spatial gradients in thermophysical properties on the topology of turbulence in heated channel flow of supercritical fluids

Boundary layer formulations in orthogonal curvilinear coordinates for flow over wind-generated surface waves

A numerical study over the effect of curvature and adverse pressure gradient on development of flow inside gas transmission pipelines

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