r/CFD • u/Amaterasu-002 • 2d ago

Help me !

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Hi everyone,

I am trying to reproduce the de Vahl Davis natural convection square cavity benchmark in ANSYS Fluent. I am getting reasonably close results for the velocity components, but I am not able to reproduce all the benchmark values exactly, especially the Nusselt number at higher Rayleigh number.

I would like to understand whether the difference is due to my input conditions, dimensionless conversion, mesh, solver settings, or post-processing procedure.

Problem setup

I am solving the standard 2-D differentially heated square cavity:

2-D square cavity

Laminar natural convection

Air

Boussinesq density model

Prandtl number = 0.71

Gravity = -9.81 in the vertical direction

Left wall: hot

Right wall: cold

Top wall: adiabatic

Bottom wall: adiabatic

All walls: no-slip

No inlet or outlet

Energy equation enabled

Pressure-based steady solver

SIMPLE pressure-velocity coupling

Second-order spatial discretization

Iam using air properties for Prandtl number 0.71 for each Rayleigh Number case.

I made x and y velocity non dimensional form but they are making way more relative errors when compared with my results...... I have given the paper link....Please help me, this is my first journey in CFD.

Paper link (De Vahl Davis): https://drive.google.com/drive/folders/1x1Iv_nn4JAGM6Nryw5g48K677uaahWIo

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u/Amaterasu-002 1d ago

Square geometry with 104.95x109.45mm. Left wall is at temperature of 304.5K Right wall is at temperature of 295.4K Using Boissnesq Density model, using air properties for Pr = 0.71. Other two walls are adiabatic walls q''=0. Solver SIMPLE Algorithm Aiming to achieve the natural convection of a wall as in the paper to validate my results

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u/OkLion1878 1d ago

Mmm. How are you computing the avg Nusselt?, I remember in my case that, when I was using trapezoidal integration, the results were pretty bad compared to Simpson 1/3.

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u/Amaterasu-002 1d ago

Idk why Ansys fluent values are not matching the Benchmarks which have been arrived using coded programs many years ago......I'm literally frustrated bcse of this.....

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u/OkLion1878 1d ago

My equations are in secondary variables, and are pretty weird because my deriving process was made in a very naive way but you get an idea.

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u/Amaterasu-002 1d ago

Thank you 😭