Aalborg Universitet CFD in Ventilation Design Nielsen, Peter Vilhelm Publication date: 2009 Link to publication from Aalborg University Citation for published version (APA): Nielsen, P. V. (2009). CFD in Ventilation Design: a new REHVA Guide Book. Aalborg: Department of Civil Engineering, Aalborg University. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research. ? You may not further distribute the material or use it for any profit-making activity or commercial gain ? You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us at [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from vbn.aau.dk on: januar 12, 2015
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Aalborg Universitet
CFD in Ventilation Design
Nielsen, Peter Vilhelm
Publication date:2009
Link to publication from Aalborg University
Citation for published version (APA):Nielsen, P. V. (2009). CFD in Ventilation Design: a new REHVA Guide Book. Aalborg: Department of CivilEngineering, Aalborg University.
General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.
? Users may download and print one copy of any publication from the public portal for the purpose of private study or research. ? You may not further distribute the material or use it for any profit-making activity or commercial gain ? You may freely distribute the URL identifying the publication in the public portal ?
Take down policyIf you believe that this document breaches copyright please contact us at [email protected] providing details, and we will remove access tothe work immediately and investigate your claim.
Computational fluid dynamics in a nutshellSymbols and glossaryMathematical backgroundTurbulence modelsNumerical methodsBoundary conditionsQuality controlCFD combined with other prediction modelsApplication of CFD codes in building designCase studiesBenchmark tests
Authors: Peter V. Nielsen (ed.), Francis Allard, Hazim B. Awbi, Lars Davidson and Alois Schälin
Computational fluid dynamics in a nutshellSymbols and glossaryMathematical backgroundTurbulence modelsNumerical methodsBoundary conditionsQuality controlCFD combined with other prediction modelsApplication of CFD codes in building designCase studiesBenchmark tests
Computational fluid dynamics in a nutshellSymbols and glossaryMathematical backgroundTurbulence modelsNumerical methodsBoundary conditionsQuality controlCFD combined with other prediction modelsApplication of CFD codes in building designCase studiesBenchmark tests
Computational fluid dynamics in a nutshellSymbols and glossaryMathematical backgroundTurbulence modelsNumerical methodsBoundary conditionsQuality controlCFD combined with other prediction modelsApplication of CFD codes in building designCase studiesBenchmark tests
Control-volume formulation (of mass fraction transport Equation in x direction):
It is necessary to replace values at the cell surfaces e and w with values at the grid points WW, W, P, E and EE to have a final version of the discretization equation.
The sixtiesThe central difference scheme becomes unstable (wiggly)when the Peclet number is large. The cure is to decreasethe grid size.
The seventiesUpwind difference opened the way for infinitely highReynolds numbers, but false diffusion could in manycases be larger than diffusion of physical kind.
The eighties and the ninetiesSecond order schemes decreased the effect of false diffusion.
The sixtiesThe central difference scheme becomes unstable (wiggly)when the Peclet number is large. The cure is to decreasethe grid size.
The seventiesUpwind difference opened the way for infinitely highReynolds numbers, but false diffusion could in manycases be larger than diffusion of physical kind.
The eighties and the ninetiesSecond order schemes decreased the effect of false diffusion.
The sixtiesThe central difference scheme becomes unstable (wiggly)when the Peclet number is large. The cure is to decreasethe grid size.
The seventiesUpwind difference opened the way for infinitely highReynolds numbers, but false diffusion could in manycases be larger than diffusion of physical kind.
The eighties and the ninetiesSecond order schemes decreased the effect of false diffusion.
Computational fluid dynamics in a nutshellSymbols and glossaryMathematical backgroundTurbulence modelsNumerical methodsBoundary conditionsQuality controlCFD combined with other prediction modelsApplication of CFD codes in building designCase studiesBenchmark tests
Computational fluid dynamics in a nutshellSymbols and glossaryMathematical backgroundTurbulence modelsNumerical methodsBoundary conditionsQuality controlCFD combined with other prediction modelsApplication of CFD codes in building designCase studiesBenchmark tests
Quality control consists of these major steps:- recognize possible sources of errors, - check for them in your own simulations, - estimate the accuracy of the simulations,- improve the simulations, if possible.
Main items in this chapter are:- Steps in a CFD simulation - Sources of errors and uncertainties- How to ensure high quality predictions (recommendations)
- Questions to ask the CFD engineer about the work reported
- Additional advice and remarks- A short check list
Computational fluid dynamics in a nutshellSymbols and glossaryMathematical backgroundTurbulence modelsNumerical methodsBoundary conditionsQuality controlCFD combined with other prediction modelsApplication of CFD codes in building designCase studiesBenchmark tests
The Regional Library of Northern Jutland is used as a testbuilding where a combination of BEPS and CFD is used forprediction of energy consumption and indoor climate.
Computational fluid dynamics in a nutshellSymbols and glossaryMathematical backgroundTurbulence modelsNumerical methodsBoundary conditionsQuality controlCFD combined with other prediction modelsApplication of CFD codes in building designCase studiesBenchmark tests
Computational fluid dynamics in a nutshellSymbols and glossaryMathematical backgroundTurbulence modelsNumerical methodsBoundary conditionsQuality controlCFD combined with other prediction modelsApplication of CFD codes in building designCase studiesBenchmark tests
Case studies on Different Air Distribution Systems
Five air distribution systems are compared with each other. They are all installed in the same room, and they all handle the same situation and the same load.
Mixing ventilation generated by a ceiling mounted radial diffuser. End wall mounted return opening below ceiling.
Displacement ventilation. End wall mounted low velocity diffuser. End wall mounted return opening below ceiling.
Vertical ventilation with a textile terminal. End wall mounted return opening at floor level.
Mixing ventilation with end wall mounted diffuser. Return opening below the supply.
The test room is the IEA Annex 20 room with length, width and height equal to 4.2 m, 3.6 m and 2.5 m.The heat load consists of two PCs, two desk lamps and two manikins producing a total heat load of 480 W. One work placeis used in some of the experiments (240 W).
LiteratureP. V. Nielsen, The Selection of Turbulence Models for Prediction of Room Airflow. ASHRAE Transactions. 1998; Vol. 104, Part 1B. -
pp. 1119-1127.
P. V. Nielsen, Indoor Climate Modelling, Chapter in: Per Erik Nilsson, Achieving the Desired Indoor Climate – Energy Efficiency Aspects of System Design. The Commtech Group, Studentlitteratur, Lund, 2003.
D. N. Sørensen and P. V. Nielsen, Quality Control of Computational Fluid Dynamics in Indoor Environments. International Journal of Indoor Environment and Health, Vol. 13, no. 1, pp. 2-17, March 2003.
A. Schälin and P. V. Nielsen, Impact of Turbulence Anisotropy near Walls in Room Air Flow. Indoor Air, International Journal of Indoor Environment and Health, Vol. 14, No. 3, pp. 159-168, 2004.
P. V. Nielsen, A. Restivo and J. H. Whitelaw, Buoyancy-Affected Flows in Ventilated Rooms, Numerical Heat Transfer, Vol. 2, 1979.
B. Bjerg, K. Svidt, G. Zhang, S. Morsing, J.O. Johnsen, Modeling of air inlets in CFD prediction of airflow in ventilated animal houses, Computers and Electronics in Agriculture, 34, 223–235, 2002
P. V. Nielsen, The Description of Supply Openings in Numerical Models for Room Air Distribution. ASHRAE Transactions, Vol. 98, Part 1, 1992.
P. V. Nielsen, The Box Method - A Practical Procedure for Introduction of an Air Terminal Device in CFD Calculation. - Aalborg: AAU, 1997. - 15 p. (R9744. - ISSN: 1395-7953).
P. V. Nielsen, The Prescribed Velocity Method - A Practical Procedure for Introduction of an Air Terminal Device in CFD Calculation. - Aalborg: AAU, 1998. - 13 p. (R9827. - ISSN: 1395-7953).
Bjerg B., Svidt K., Morsing S., Zhang G, Comparion of Methods to Model a Wall Inlet in Numerical Simulation of Airflow in Livestock Rooms, Proceedings of AgEng2000, International Conference on agricultural engineering, Warwick, UK, 2000.
L. Davidson, P. V. Nielsen and A. Sveningsson, Modifications of the Model for Computing the Flow in a 3D Wall Jet. Submitted to THMT-03, International Symposium on Turbulence, Heat and Mass Transfer, October 12 – 17, 2003, Antalya, Turkey.
L. Davidson, P. V. Nielsen and C. Topp, Low-Reynolds Number Effects in Ventilated Rooms: A Numerical Study. In: Proceedings of ROOMVENT 2000, Reading, 2000.