Explicit Algebraic Reynolds-stress Modelling of a Convective Atmospheric Boundary Layer Including Counter-Gradient Fluxe
- PDF / 522,894 Bytes
- 11 Pages / 439.37 x 666.142 pts Page_size
- 78 Downloads / 184 Views
Explicit Algebraic Reynolds-stress Modelling of a Convective Atmospheric Boundary Layer Including Counter-Gradient Fluxes Velibor Želi1
· Geert Brethouwer1
· Stefan Wallin1
· Arne V. Johansson1
Received: 26 May 2020 / Accepted: 9 October 2020 © The Author(s) 2020
Abstract In a recent study (Želi et al. in Bound Layer Meteorol 176:229–249, 2020), we have shown that the explicit algebraic Reynolds-stress (EARS) model, implemented in a single-column context, is able to capture the main features of a stable atmospheric boundary layer (ABL) for a range of stratification levels. We here extend the previous study and show that the same formulation and calibration of the EARS model also can be applied to a dry convective ABL. Five different simulations with moderate convective intensities are studied by prescribing surface heat flux and geostrophic forcing. The results of the EARS model are compared to large-eddy simulations of Salesky and Anderson (J Fluid Mech 856:135–168, 2018). It is shown that the EARS model performs well and is able to capture the counter-gradient heat flux in the upper part of the ABL due to the presence of the non-gradient term in the relation for vertical turbulent heat flux. The model predicts the full Reynolds-stress tensor and heat-flux vector and allows us to compare other important aspects of a convective ABL such as the profiles of vertical momentum variance. Together with the previous studies, we show that the EARS model is able to predict the essential features of the ABL. It also shows that the EARS model with the same model formulation and coefficients is applicable over a wide range of stable and moderately unstable stratifications. Keywords Convective boundary layer · Counter-gradient heat flux · Reynolds-stress model · Turbulence modelling
1 Introduction Turbulence parametrization schemes that are used for physical parametrization of the atmospheric boundary layer (ABL) are usually tailored with disparate descriptions for stable and unstable stratification, or sometimes even for different levels of stratification (see He et al. 2019). An attractive alternative is a turbulence model with sufficiently general formulation
B 1
Velibor Želi [email protected] Department of Engineering Mechanics, FLOW Centre, KTH Royal Institute of Technology, 10044 Stockholm, Sweden
123
V. Želi et al.
that enables accurate predictions of both the stably stratified and convective ABL. One challenge with the latter is the existence of counter-gradient heat fluxes in the upper part of the convective ABL. These fluxes are usually modelled with additional non-gradient terms (see Holtslag and Moeng 1991; Siebesma et al. 2007) in addition to an eddy-diffusivity type of terms. Lazeroms et al. (2013) derived the so-called explicit algebraic Reynolds-stress (EARS) model for the general case of stratified flows and applied it in the context of the ABL (Lazeroms et al. 2015, 2016). The EARS model is based on transport equations for Reynolds-stress tensor and heat-flux vector, i.e., turbulence momentum and
Data Loading...
