Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 1

The IEA Annex 20 Two-Dimensional Benchmark Test for CFD Predictions

by

Peter V. NielsenAalborg University

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 2

The Background for the 2D Case

Urbach (1971) Ego (1970)

Scwenke (1975) Restivo (1979)

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 3

2D Test Case

See:www.cfd-benchmarks.com

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 4

Publications of 2D Test Cases oncfd-benchmarks.com

7PhD - thesis

6IEA Annex 20

22005 - 2010

102000 - 2004

101995 – 1999

81990 - 1994

41989 and before

… and several more publicationsfrom e.g. internal PhD courses.

They all cover different aspectsas:• grid dependency• numerical schemes• different source codes• different turbulence models• different length scales in a

supply opening• etc…

The comparison withmeasurements can beextended by the information obtained by comparisonwith other predictions.

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 5

Decisions to make before making a CFD Prediction

Is the flow:Laminar or turbulent?

Is the flow:Two-dimensional or three-dimensional?

Is the flow:Steady or unsteady?

Has the flow:One, two or several solutions?

Has the flow a symmetry plane?

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 6

Decisions to make before making a CFD Prediction

Is the flow:Laminar or turbulent?

Is the flow:Two-dimensional or three-dimensional?

Is the flow:Steady or unsteady?

Has the flow:One, two or several solutions?

Has the flow a symmetry plane?

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 7

Two-Dimensional Steady State Prediction of the Flow

Skovgaard and Nielsen (1991)

LRN k–ε model

Velocity ~ RMS

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 8

Two-Dimensional Steady State Prediction of the Flow

Streamlines: k-ε, k-ω, BSL and SST models

k-ε model k-ω model

BSL model SST model

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 9

Decisions to make before making a CFD Prediction

Is the flow:Laminar or turbulent?

Is the flow:Two-dimensional or three-dimensional?

Is the flow:Steady or unsteady?

Has the flow:One, two or several solutions?

Has the flow a symmetry plane?

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 10

Three-Dimensional Steady State Prediction of the Flow

Streamlines: k-ε, k-ω and SST models

h/H = 0.056, L/H = 3.0 and W/H = 1.0

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 11

Three-Dimensional Steady State Prediction of the Flow

Streamlines for the k-ω model

Experiments

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 12

Decisions to make before making a CFD Prediction

Is the flow:Laminar or turbulent?

Is the flow:Two-dimensional or three-dimensional?

Is the flow:Steady or unsteady?

Has the flow:One, two or several solutions?

Has the flow a symmetry plane?

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 13

Three-Dimensional Unsteady Flow

Davidson and Nielsen (1996)

Large Eddy Simulation (LES)

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 14

Three-DimensionalUnsteady Flow

Davidson and Nielsen (1996)

Large eddy simulation and probability density function

Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 15

UnsteadyFlow?

Will a 3D unsteadyRANS solution givemore similar solutionsfor the differentturbulence models?

Thank you very much!