# Natural convection in a space-dependent gravity field

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 LinkBack Thread Tools Search this Thread Display Modes
 April 14, 2022, 04:14 Natural convection in a space-dependent gravity field #1 New Member   Hajar Join Date: Feb 2022 Location: Fr Posts: 1 Rep Power: 0 Hello, I am modelling a natural convection problem in a cylindrical cavity heated from below. The primary objective is to study the influence of a variable gravitational field on the flow patterns and temperature distribution (Fig.1). A steady State (Pseudo transient) K-omega SST model is used. geometry.PNG First simulations were ran considering a uniform gravity field by defining the gravity components in the “Gravity” box in “General” (-9.81 m/s² in x component); satisfying convergence and physical results were obtained. The next step is to assign a variable gravitational field (g*=f(x,y)) for gravity, to that end, I defined gravity components as profiles and assigned them to axial and radial momentum source terms. These accelerations are actually are calculated with a Matlab code and would be complicated to implement on Fluent (Complex Integrals). In order to check how these source terms are implemented in the equations, I ran a first simulation, using a constant x-component gravity profile (9.81 m/s² in all cells), defined a Named Expression (Density*(‘gravity_profile’) and assigned it to the x-momentum source term. The aim is to compare it to the case where gravity is assigned through the “Gravity” box. Unfortunately, the solutions were different. After investigation, I found out that the problem comes from the buoyancy effects on turbulence production. When gravity is enabled through the gravity box, the option “Buoyancy effects” appears in the k-omega SST box and disappears if not. The figures below illustrate the difference between the solutions: results.jpg Noticing that the buoyancy effects are probably behind this difference, I tried calculating the source terms due to buoyancy in the kinetic energy and dissipation rate equations as suggested in the Fluent Theory Guide (Gb and Gbw) and assigned them to a case where gravity is enabled and the buoyancy effects are switched off. Unfortunately, I do not get the same result as the case where the buoyancy effects are enabled. My questions are: -Is it possible to assign the gravity field as a profile in the “Gravity” box? -If not, and if I have to define gravity as a source term, in that case how can I consider buoyancy effects on turbulence to include it in the k-W equations? Thank you,

 Tags gravity, natural convection, profiles, source terms, turbulence generation

 Thread Tools Search this Thread Search this Thread: Advanced Search Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post emat OpenFOAM Running, Solving & CFD 1 March 28, 2017 08:37 WhiteW OpenFOAM Running, Solving & CFD 16 December 20, 2016 00:51 rohan1255 FLUENT 3 April 5, 2016 18:56 marzoa STAR-CCM+ 0 April 18, 2011 14:12 max91 CFX 1 July 29, 2008 20:28

All times are GMT -4. The time now is 18:09.

 Contact Us - CFD Online - Privacy Statement - Top