The aim of this project is to simulate the flow field around Petronas Towers using SimScale platform. The twin tower structure raises the urge to investigate the vorticity induced due to the upstream structure and its possible effects on the twin tower. For civil structures the vortex induced vibration is an interesting phenomenon that might effect the serviceability of the structure. The point of separation in the flow due to the upstream section, varies with the wind speed and the altitude due to the varying cross section of the structures. For simplification, the problem was simulated for a steady inflow wind speed of 10 m/s. A more realistic approach would be considering the altitude varying wind speed e.g. PowerLaw or Loglaw as well as inflow turbulence.
Structure and mesh
The structure is in the real scale i.e. height of 440 m (for this part of the structure excluding the tower entrance building). For simulating the flow field, the bounding box is 3000 m along the wind direction (Y) , 1500 m for the perpendicular axis (X) and 750 m along the height (Z). For mesh creation automatic snappy hex mesh for external flows was used, that was sufficient to produce a mesh with fine quality, specially in the interesting zones in the neighbourhood of the two towers.
For the numerical analysis a Steady-state Incompressible fluid flow type was selected with K-Omega-SST turbulence model. The analysis was carried out on 32 cores and took ca 7 minutes.
The simulation results were downloaded from SimScale platform and the Post processing was done locally using ParaView.
1. Multi slice post-processing to visualise the vortex separation at different altitudes.
Velocity contour field as well as streamlines are plotted for each slice along the altitude of the structure.
At height 100 m
At height 150 m
At height 250 m
At height 350 m
For the simulated wind speed (10 m/s) and the assumptions of steady inflow the flow separation is not occurring in the space between the two towers, except at higher altitudes i.e. as the cross section is smaller. A more realistic simulation should consider that the wind speed would be higher as well at such altitudes and consequently the separation is more likely to happen.
In the following figures another perspective of the streamlines is shown showing the three dimensional nature of the flow.
The stream lines along the height of the structure, the change in the flow separation along the height is shown.
Stream lines along the height as well as those in a horizontal slice at altitude of 100 m are shown in the figure below. the 3D nature of the flow is presented by illustrating the 3D eddies created in the vicinity of the flow.
It is crucial to mention that for simulations of wind flow around civil structures specially line-like structures, an approach of multi 2D simulation is often proposed as a computationally cheaper alternative to full 3D simulations. However that implies that the 3D structures in the flow e.g. the 3D eddies depicted in the figure below would be neglected (For example below in section 3).
2. Pressure Contours.
3. Comparison of the results to results obtained by Discrete Vortex Method.
For validating the obtained results, the same problem was simulated using another approach based on Particle Vortex Method. In which, the three-dimensional structure is simulated in a series of two-dimensional Computational Fluid Dynamics simulation slices, utilizing the Vortex Particle Method (VPM). The fluid simulation slices are placed at discrete locations along the axis of the structure. The Lagrangian nature of the VPM proposes it as an efficient numerical technique for incompressible flow simulations, e.g. in the context of wind engineering. This numerical technique provides an alternative to classical Eulerian methods such as finite volume. The formulation and the discretisation of the Navier-Stokes equations in the VPM reflects the natural representation of the vortex creation process, which is inherent in flows around bluff bodies. Additionally, the method accounts for free-space boundary conditions. Nevertheless due to the coupled 2D simulations, the 3D vortices naturally existing in the flow are neglected.
Below the separation in the flow happenning at altitude of 350 m is presented as well, this time using the VPM method.