Natural convection in a cavity with time-varying thermal forcing on a sidewall. (April 2020)

• Record Type: Journal Article
• Authors: Zhou, L.; Armfield, S.W.; Williamson, N.; Kirkpatrick, M.P.; Lin, W.
• Is Part Of: International journal of heat and mass transfer. Volume 150(2020)
• Publication Date: 2020-04
• Subjects: Natural convection in a cavity -- Unsteady forcing; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2019.119234
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Detailed descriptions of the periodic flow and temperature fields in a cavity subjected to a time-varying thermal forcing. Three flow regimes identified at low, intermediate and high forcing frequencies, characterised by the cavity filling time, the boundary layer development time and the forcing period. Scaling relations for the time average stratification in terms of the forcing frequency obtained for high and low frequency ranges. Rayleigh number dependency of the flow described. Abstract: Transient natural convection flow is investigated in a two-dimensional square enclosure, subjected to periodic heating and cooling on one sidewall. The thermal forcing applied on the heated sidewall varies with time as a sine wave around a zero mean at a frequency f, with all other walls adiabatic. The time-varying heating/cooling produces an alternating direction vertical natural convection boundary layer that entrains fluid from the cavity interior and discharges it alternatively at the top and bottom of the cavity. The behaviour of the flow is governed by three characteristic time scales, the forcing period, 1/ f, the development time for the boundary layer and the filling time of the cavity. For low forcing frequency the filling time is less than the forcing period and the time average stratification S ¯ is well approximated by S ¯ ∼ f 4 / 5 . For high forcing frequency the forcing period is smaller than the boundary layer development time and S ¯ ∼ f − 2 . The maximum S ¯ occurs in a transition region, between the low and high frequency ranges. The maximum value of S ¯ increases with increasing Rayleigh number, approaching S ¯ ≅ 1.0 for the highest values of Rayleigh number considered.