Passive scalar transport in a turbulent spot within a poiseuille flow. (1st June 2023)

• Record Type: Journal Article
• Authors: Arrondeau, Benjamin; Tardu, Sedat; Doche, Olivier
• Is Part Of: International journal of heat and mass transfer. Volume 206(2023)
• Publication Date: 2023-06-01
• Subjects: Passive scalar -- Heat transfer -- Transitional spot -- Poiseuille flow; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2023.123930
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Temperature transport in a turbulent spot is investigated by high resolution DNS Mixing is larger in the transitional spot compared to wall turbulence Passive scalar transport is similar to wall turbulence in the spot turbulent core Wave area of the spot drastically increases the temperature fluctuations Quasi-streamwise vortices are organized into clusters on the outskirts of the spot Abstract: A pair of counter-rotating vortices are introduced in a Poiseuille flow to trigger the by-pass transition. The accent is put on the passive scalar transport within the resulting transitional spot. The latter is identified and tracked in time and space using the fluctuating vorticity and temperature fields it induces. The velocity and temperature statistics are determined strictly within the spot. They are scaled by the inner variables, related to the shear velocity and the wall temperature flux induced by the spot. The statistics are compared with those of the corresponding fully developed turbulent channel flow, in order to determine the degree of similarity between the internal structure of the spot and the fully developed wall turbulence. The analysis includes the fine structure of the fluctuating temperature field, its transport equations and the effect of the coherent structures within the spot. It is found that the turbulent part of the spot is closely similar to the turbulent wall flow, both for the fluctuating flow, and the passive scalar fields. The root-mean-square of the temperature fluctuations determined in the entire spot is nearly twice larger than that in the fully developed wall turbulence in the outer part of the flow. The transport is enhanced and the turbulent fluxes increase compared to the fully developed turbulent channel flow. This is due to the wave area of the spot that contains, in their great majority, the structures coming from the breakdown process of waves. The latter is responsible for the increase of the small-scale mixing and of the large peripheral temperature fluctuations, which is rather good news from an application point of view.