The onset of natural convection in lakes and reservoirs due to night time cooling

Abstract

A theoretical model, based on linear stability analysis, is proposed to predict the onset of natural convection in lakes and reservoirs due to night time cooling. To such purpose, the system was modelled as a initially quiescent deep Boussinesq fluid reservoir, whose upper boundary temperature changes sinusoidally. From scaling analysis, it is found that critical onset times for convection are proportional to R −2/7 , where R is a Rayleigh number including fluid properties and forcing frequency. The proportionality constant was found, from the solution of an eigenvalue problem, as a function of the Prandtl number. The onset time for convection was easily observed from experiments and quantitatively detected as a rapid increase of the RMS of the computed velocity field obtained using PIV. In this controlled conditions, differences close to 10% between predicted and observed times for the start of the convective flow was found. It is apparent from the present set of results that predictions are reasonable.

Destratification of thermally stratified turbulent open-channel flow by surface cooling

“…These studies have found that turbulence statistics and bulk quantities such as entrainment rate scale in terms of a convection velocity (Deardorff 1970) that is a function of the surface buoyancy flux and mixed layer height. Deardorff et al (1980) found that the entrainment rate scales with a convection Richardson number according to a simple power law relationship, This and similar scaling relationships based on have been used extensively to parameterise thermal convection processes that occur in the atmospheric boundary layer, as well as in large water bodies such as oceans and lakes (see Marshall & Schott 1999; Fedorovich et al 2004; Ihle & Niño 2012; Bouffard & Wüest 2019, for reviews).…”

“…This and similar scaling relationships based on w * have been used extensively to parameterise thermal convection processes that occur in the atmospheric boundary layer, as well as in large water bodies such as oceans and lakes (see Marshall & Schott 1999;Fedorovich et al 2004;Ihle & Niño 2012;Bouffard & Wüest 2019, for reviews). The remainder of this paper is structured as follows.…”

Impact of uniform and non-uniform heated rods on free convective flow inside a porous enclosure: finite element analysis

“…Natural convection has attracted the interest of many researchers because of its wide range applications in many fields of technology and science. Which comprises of food storage industry, geophysics, atmospheric sciences, astrophysics, metallurgical industries, petroleum industries, heating and drying process, thermal power, fire control, cooling of electronic equipment, nuclear reactor, built-in storage solar collector, crystal growth, lake and reservoirs, solidification processes, heating and drying process, sterilization of canned food, construction and thermal insulation [1][2][3][4][5][6][7][8][9]. Natural convection depends on the geometry of enclosure, thus understanding of thermal distribution and fluid flow in several enclosures is considered as crucial challenge.…”