By Michael Rothenborg
Marie Skytte Thordal is not out to make wind tunnels obsolete. She just wants to make constructing higher buildings easier, cheaper and more efficient.
That’s why the Industrial PhD Student and Ramboll engineer has spent so much time between wind tunnels, skyscraper models and high-powered computers in one of the big experimental labs at the Technical University of Denmark (DTU) just outside Copenhagen.
The skyscraper models are the product of growing demand for high-rise buildings - a trend that Ramboll and other companies in the construction business have noted.
“Wind load has a great impact on the structural construction design of high-rise buildings, for which reason structural engineers are seeking to optimize the wind load on buildings by conducting wind tunnel tests and modifying how buildings are shaped,” Marie Skytte Thordal explains.
Her work is performed together with the Advanced Flow Consulting team in Ramboll with more than 15 years of experience in complex flow problems.
Faster and easier digital design
Wind loads on structures within built environment is an ever-present task which many areas need to address when designing or trouble shooting a structure. Computational Fluid Dynamics (CFD) has the ability to model the real-world physics and displaying it, revealing what is actually happening. Thus, making the digital design evaluation faster and easier.
"Traditionally, the wind load is determined by estimation and wind tunnel study", explains Jens Chr. Bennetsen, Project Director at Ramboll Transport: "However, the wind tunnel studies are more rigid and often only a single study is performed during the design process for a high-rise building. Thereby less interaction and optimization of form and sharp can be integrated".
Ramboll are implementing the Digital Wind Tunnel approach which is based on the use of CFD modelling for assessment the wind flow. This paves the way for faster design evaluations and shedding clear light on the wind physics and providing complex information in an illustrative way.
One of the corner stones are accuracy, where Marie Skytte Thordal is working on enhancing the understanding and integration of the Digital Wind Tunnel approach at the DTU.
3D model reduces cost
Using wind tunnels – whose design is not particularly adaptable – to establish wind loads can be expensive and time consuming in a design process where the architecture is under constant modification. Marie Skytte Thordal proves her point with one of her own skyscraper models.
“Testing whether a building design is better with rounded corners than with sharp edges means having to build an all-new model – and I now know how cumbersome that can be,” she says, nodding at the town model and all the tubes in the wind tunnel.
Ramboll is familiar with this problem from its consultancy role on Bella Sky, Carlsberg City and other buildings with complex structures, where it was necessary to wait for – and put full trust into - an external wind tunnel expertise.
In recent years challenges like these have increased demand for digital methods like the 3D air simulation tool Computational Fluid Dynamics (CFD). CFD can reduce time consumption and ensure faster response times in the design process.
“Using digital methods creates great opportunities and freedom because different designs can be tested within a short period, and the architectural 3D model can be used directly in the CFD simulation,” Marie Skytte Thordal explains.
However, in Denmark CFD has yet to become a fully proven and accepted method for determining wind load in engineering practice. Throughout this on-going study it is readily being applied for early design phase and project where wind tunnel due to scale are not suited.
Maria Skytte Thordal has completed part of her PhD in Japan – a leading country in this field. The Japanese implement CFD in the structural design phase, thanks in part to ultra-fast supercomputers capable of making the complicated calculations required to validate the 3D simulation tool for wind tunnel tests.
“I hope to ensure that CFD truly produces considerable advances for the construction industry in Denmark and other parts of Europe. Furthermore, the results can also underpin a closer collaboration between architects and engineers in the future – and thus provide better products for customers,” says Marie Skytte Thordal.