## 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

5 results

## Search Results

Now showing 1 - 5 of 5

Publication Marginally turbulent flow in a square duct(Cambridge University Press, 2007) Uhlmann, Markus; Pinelli, Alfredo; Kawahara, Genta; Sekimoto, AtshushiA direct numerical simulation of turbulent flow in a straight square duct was performed in order to determine the minimal requirements for self-sustaining turbulence. It was found that turbulence can be maintained for values of the bulk Reynolds number above approximately 1100, corresponding to a friction-velocity-based Reynolds number of 80. The minimum value for the streamwise period of the computational domain is around 190 wall units, roughly independently of the Reynolds number. We present a characterization of the flow state at marginal Reynolds numbers which substantially differs from the fully turbulent one: the marginal state exhibits a four-vortex secondary flow structure alternating in time whereas the fully turbulent one presents the usual eight-vortex pattern. It is shown that in the regime of marginal Reynolds numbers buffer-layer coherent structures play a crucial role in the appearance of secondary flow of Prandtl's second kind.Publication Coherent structures in marginally turbulent square duct flow(Springer, 2008) Uhlmann, Markus; Pinelli, Alfredo; Sekimoto, Atshushi; Kawahara, Genta; Kaneda, YukioDirect numerical simulation of fully developed turbulent flow in a straight square duct was performed in order to determine the minimal requirements for self-sustaining turbulence. It was found that turbulence can be maintained for values of the bulk Reynolds number above approximately 1100, corresponding to a friction-velocity-based Reynolds number of 80. The minimum value for the streamwise period of the computational domain measures around 190 wall units, roughly independently of the Reynolds number. Furthermore, we present a characterization of the marginal state, where coherent structures are found to have significant relevance to the appearance of secondary flow of Prandtl’s second kind.Publication The eﬀect of coherent structures on the secondary ﬂow in a square duct(Springer, 2009) Sekimoto, Atshushi; Pinelli, Alfredo; Uhlmann, Markus; Kawahara, Genta; Eckhardt, BrunoThe appearance of secondary flow of Prandtl’s second kind is a well-known phenomenon in fully developed turbulent rectangular duct flow. The intensity of the secondary flow is two orders of magnitude smaller than that of the mean streamwise velocity; however, it plays an important role in the crossstreamwise momentum, heat and mass transfer. Our recent study [1] revealed that the mean secondary flow is a statistical footprint of the turbulent flow structures, i.e. streamwise vortices and streaks which are observed in the nearwall region, whose cross-sectional positions are constrained by the presence of the side walls at marginal Reynolds number (approximately 1100, based on the bulk velocity and the duct half width, corresponding to a friction Reynolds number of about 80). In this marginal case, one low-speed streak associated with a pair of counter-rotating streamwise vortices can exist over each wall and they are self-sustained [2]. When considering the higher Reynolds numbers, the increment of duct width in wall unit allows the simultaneous presence of multiple low velocity streaks and pairs of streamwise vortices upon the wall.Publication Characterisation of marginally turbulent square duct flow(Springer, 2007) Uhlmann, Markus; Pinelli, Alfredo; Sekimoto, Atshushi; Kawahara, Genta; Palma, J.L.M.L.; Silva Lopes, A.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.