4 - Integration of CFD

Article No. 4 

Integration of CFD in Structural and Architectural Wind Engineering 

Academic Ph.D. Project (November 2009 - October 2012)

Student: Nina Gall Jørgensen
Supervisors: Holger H. KossChristos T. Georgakis ; Lotte B. Jensen  

Background and Motivation

Wind effects on building structures and on the urban environment have traditionally been investigated by means of wind tunnel testing. During the last years, the application of numerical simulation methods such as Computational Fluid Dynamics (CFD) has become an increasingly integrative part of studies dealing with wind flow. Propelled by the fast development in computational capacity and performance and continuous improvement of commercially provided software packages the usage of CFD becomes more and more attractive as a working tool for researchers, engineers and architects. Amongst many advantages the comprehensive graphical appearance of results appeals also to non specialists in this field and suggests CFD as the ideal tool for airflow or wind studies in a broad sense of possible applications. In spite of the above mentioned advantages the quality assurance of the application is closely related to the user’s knowledge in CFD modeling [1]. To address specific problems of complex physical nature existing guidelines still remain insufficient also due to their tendency to generalize.

Architectural aerodynamics in particular focuses on the effects of wind on the function of urban spaces and buildings. In many cases the particular architectural design of a building puts the structure outside the application field of codes and standards for structural design. As a consequence simulation-based investigation of the wind-induced load is required.

In general one can describe the field of wind engineering as a discipline dealing with the interaction between the wind in the atmospheric boundary layer and man and his works on the surface of the earth. This implies two major challenges for CFD modeling, namely the complexity of atmospheric airflow and the large-scale subject of the studies. Furthermore, the detailed problematic studied in structural and architectural wind engineering requires a high performance of simulation with respect to modeling the physics of the fluid mechanical phenomena and to numerical errors and uncertainties. For the prediction of wind loads for structural design the stochastic process of the loading must be simulated accurately. In wind tunnel tests this is normally achieved by a proper generation of the turbulent wind in the atmospheric boundary layer (ABL flow) applying the relevant scaling laws and by using an appropriate measurement system capable of picking up the high frequent quantities of the load process.

When using CFD the simulation of the wind load process is according to [3] additional discriminated by the errors and uncertainties in modeling the physical and numerical errors and uncertainties. Due to complexity of the physics and large-scale area coverage  problems,  in structural and architectural wind engineering, are mainly addressed with stationary approaches (RANS and URANS) where guideline advice is to some extent available ([1],[4]). However, recent works, for example [5], show that non-stationary approaches such as large eddy simulations (LES) do provide that type of information upon which structural is based.

Green Architectural views cities as new and different structures, and buildings as "intelligent", so that they are not only self-sufficient but also make a positive contribution to their surroundings, create biological diversity and produce cleaner air [6]. 

Figure 1: Tower of Tomorrow – Project, Frankfurt am Main

Germany, 2007, William McDonough + Partners
 

In connection to sustainable design architects experiment with novel approaches for building structures, energy saving or even producing façades and urban infrastructure. Architectural sustainability means taking one’s point of departure in the environment to such an extent that the buildings are created for the specific environment, with due allowances for specific climatic conditions like sun, wind and compass orientation ([Figure 1, [6]). Consequently, architectural wind engineering has to provide tools that allow for evaluating the design with respect to the intended goals.

The objective of this proposed research project is to examine the capabilities of CFD for the investigation of issues within architectural wind engineering. Particular focus shall be on following aspects:

  • Wind load on individual feature and on the global structure.
  • Performance of green facades with respect to thermodynamic effects and influence on the wind environment around the building.
  • Prediction of measurable quantities considered as fundamental criteria in the quality assessment of open urban spaces.

The research should expand the knowledge for proper application of CFD codes and provide a basis for a best practice guideline (BPG). Existing results from wind tunnel tests and additional testing will be used to validate the numerical simulations.

References related to this Research Project: 

[1] Franke, J. et al., (2007). “Best practice guideline for the CFD simulation of flows in the urban environment”, COST Action 732, “Quality assurance and improvement of microscale meteorological models”, May 2007
[2] Casey, M., Wintergerste, T., (2000). “Quality and trust in industrial CFD”, Best Practice Guidelines, ERCOFTAC, 2000
[3] Coleman, H.W., Stern, F. (1997), “Uncertainties and CFD code validation”, Journal of Fluids Engineering, Vol. 119, pp. 795-803, 1997
[4] Yang, W. et al. (2008). “Influences of equilibrium atmospheric boundary layer and turbulence parameter on wind loads of low-rise buildings”, Journal of Wind Engineering and Industrial Aerodynamics, Vol. 96, pp. 2080-2092, 2008
[5] Tamura, T. (2008). “Towards practical use of LES in wind engineering”, Journal of Wind Engineering and Industrial Aerodynamics, Vol. 96, pp. 1451-1471, 2008
[6] Louisiana – Museum of Modern Art (2009). “Green architecture for the future”, Exhibition, May 29 – December 18, 2009

Ongoing Research Work:

Spring 2010:
Comparison of wind tunnel experiments and CFD simulations with particular focus on flow properties. The experimental work will be performed in the Research and Educational Wind Tunnel (R&EWT) at the Department of Civil Engineering. Different flow types will be generated, from uniform laminar flow to a turbulent boundary layer flow. The latter puts high demands to computational simulation, especially if the turbulent flow needs to generated as a time process (transient simulation). Based on a relatively simple setup experimental results shall be compared to different CFD simulations, e.g. RANS, URANS and LES.