## Person: Pinelli, Alfredo

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##### First Name

Alfredo

##### Last Name

Pinelli

##### Affiliation

Universidad Complutense de Madrid

##### Faculty / Institute

Ciencias Matemáticas

##### Department

##### Area

Matemática Aplicada

##### Identifiers

2 results

## Search Results

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Publication Turbulence-and buoyancy-driven secondary flow in a horizontal square duct heated from below(American Institute of Physics, 2011) Sekimoto, Atshushi; Kawahara, Genta; Sekiyama, K.; Uhlmann, Markus; Pinelli, AlfredoDirect numerical simulations of fully developed turbulent flows in a horizontal square duct heated from below are performed at bulk Reynolds numbers Re(b) = 3000 and 4400 (based on duct width H) and bulk Richardson numbers 0 <= Ri <= 1.03. The primary objective of the numerical simulations concerns the characterization of the mean secondary flow that develops in this class of flows. On one hand, it is known that turbulent isothermal flow in a square duct presents secondary mean motions of Prandtl's second kind that finds its origin in the behavior of turbulence structures. On the other hand, thermal convection drives a mean secondary motion of Prandtl's first kind directly induced by buoyancy. As far as the mean structure of the cross-stream motion is concerned, it is found that different types of secondary flow regimes take place when increasing the value of the Richardson number. The mean secondary flow in the range 0.025 less than or similar to Ri less than or similar to 0.25 is characterized by a single large-scale thermal convection roll and four turbulence-driven corner vortices of the opposite sense of rotation to the roll, as contrasted with the classical scenario of the eight-vortex secondary flow pattern typical of isothermal turbulent square-duct flow. This remarkable structural difference in the corner regions can be interpreted in terms of combined effects, on instantaneous streamwise vortices, of the large-scale circulation and of the geometrical constraint by the duct corner. When further increasing the Richardson number, i.e., Ri greater than or similar to 0.25, the structure of the mean secondary flow is solely determined by the large-scale circulation induced by the buoyancy force. In this regime, the additional mean cross-stream motion is characterized by the presence of two distinct buoyancy-driven vortices of opposite sense of rotation to the circulation only in two of the four corner regions. With increasing Ri, the large-scale circulation is found to enhance the wall skin friction and heat transfer. In the significant-buoyancy regime Ri greater than or similar to 0.25, the mean cross-stream motion and its rms fluctuations are found to scale, respectively, with the buoyancy-induced velocity u(g)=root g beta Delta TH (g, beta, and Delta T being the gravity acceleration, the volumetric coefficient of thermal expansion, and the temperature difference across the duct, respectively) and with the mixed velocity scale root(nu/H)u(g) (nu being the kinematic viscosity). It is suggested that the probable scalings for the rms of streamwise velocity component and of temperature fluctuation are related with the friction velocity u(tau) and friction temperature T(tau) according to the magnitudes u(tau)(2)/ and T(tau)u(tau)/root(nu/H)u(g), respectively.Publication Buoyancy effects on low-Reynolds-number turbulent flow in a horizontal square duct(Begell House, 2009) Sekimoto, Atshushi; Sekiyama, K.; Kawahara, Genta; Uhlmann, Markus; Pinelli, AlfredoDirect numerical simulations of fully developed low-Reynolds-number turbulent flow in a horizontal square duct heated from below are performed at Richardson numbers 0 ≤ Ri ≤ 1.03 to investigate the buoyancy effects on the coherent structures near the walls, i.e. streamwise vortices and associated streaks, and on turbulence-driven secondary flow of Prandtl's second kind. It is found that cross-streamwise thermal convection which is represented by single large-scale circulation appears to affect the coherent structures and the mean secondary flow for Ri ≥ 0.02. As Ri is increased, the nearwall coherent structures are observed to appear more frequently in the region near one of the two corners on the wall, since they are swept along the wall towards the corner by the large-scale convection. The localization of the near-wall structures affects the profile of skin friction and heat transfer rate on the wall.