Flow Features in a Fully Developed Ribbed Duct Flow as a Result of MILES

Abstract

The present contribution describes the topology associated with the turbulent flow in a square duct partially blocked by a rib of square section mounted on a single wall. The flow is simulated by means of a MILES method and the resulting velocity fields are analysed using the concepts of stream surface, vortex core detection, wall streamline and bifurcation line. Instantaneous and time averaged coherent structures are extracted applying the second scalar invariant of the velocity gradient tensor (so-called Q criterion), respectively, to the instantaneous and time averaged velocity fields. This postprocessing reveals significant 3D effects induced by the geometry, namely the influence of the side walls, which is clearly identified. The combination of the different visualisation techniques offers a complement to the standard representation based on Eulerian statistics and contributes to a deeper understanding of this complex flow.

On the highly unsteady dynamics of multiple thermal buoyant jets in cross flows

“…Moreover, following the analyses by Nakayama and co-workers (Nakayama and Nagai 102 ; Nakayama et al, [103][104][105][106][107] ), who performed LESs of turbulent flows in the atmospheric boundary layer with thermal plumes for a variety of conditions (0.12Ri0.45, Re=O(10 5 ) obtaining good agreement with dedicated experiments, in the present paper we assume Cs=0.1 (notably, Li and Ma 71 used the same value of Cs for pure thermogravitational convection, i.e. Re=0 while Ciofalo and Collins 72 , and Lohász et al, 75 yet assumed Cs=0.1 for rib-roughened channels in the opposite condition for which there was no thermal buoyancy, i.e. Ra=0).…”

“…Ma and Li 56 ; Xiao et al, 57 ; Harish and Venkatasubbaiah 58,59 ; Tsai et al, 60 ; Weihing et al, 61 ; Lou et al, 62 ), for the case of highly unsteady dynamics, LES (Large Eddy Simulation) seems to be a more relevant choice, especially when the phenomena of vortex coalescence and splitting become pervasive throughout the computational domain. The LES approach has been successfully applied to pure thermal convection (Eidson 54 ; Wong and Lilly 63 ; Kimmel and Domaradzki 64 ; Pham et al, 65 ; Yan 66 ; Devenish et al, 67 ; Pant and Bhattachary 68 ), circumstances involving various kinds of jets in cross flow (Morton et al, 69 ; Li and Wang 70 ; Li and Ma 71 ) and flows (without buoyancy) in ducts with "turbulators" (Ciofalo and Collins 72 ; Murataa and Mochizuki 73 ; Cui et al, 74 ; Lohász et al, 75 ;…”

Simulation of the Flow in a Ribbed Rotating Duct with a Hybrid k-ω RANS/LES Model

“…These vortices are magnified by the movement towards the ribbed wall in the centre of the duct downstream of a rib. The generation of rib-induced vortices was clearly demonstrated by PIV measurements in cross-sections of a stationary duct with square orthogonal ribs on one side by Casarsa and Arts [28] and by LES of the flow in the same ribbed duct by Lohasz et al [29]. The second phenomenon is the Coriolis force induced transversal flow in side-wall boundary layers from the pressure side wall to the suction side wall.…”

Film Cooling Extraction Effects on the Aero-Thermal Characteristics of Rib Roughened Cooling Channel Flow

“…The current geometry (absent of cooling holes) has previously been investigated in several studies at the von Karman Institute, each focusing on a different aspect of the problem, with added complexity [10][11][12][13]. The current heat transfer study builds upon this complementary database of information, acquired by the experimental and numerical prior work.…”