Pressure on Buildings (CAARC)

The CAARC (Commonwealth Advisory Aeronautical Research Council) building is the standard benchmark for wind pressure on high-rise structures. Its simple rectangular geometry and well-documented experimental database make it the canonical first test for any wind pressure workflow: if a solver can reproduce the mean and fluctuating pressure distribution on CAARC, the methodology is trustworthy for production runs on real buildings.

This guided case walks you through setting up a single-direction wind pressure simulation for the CAARC geometry in AeroSim. The output is a mean surface pressure distribution - the Cp map on the windward, leeward, and side faces - along with RMS pressure fluctuations. The same setup scales directly to real building geometries and multiple wind directions.

Case Description

The CAARC building is a rectangular prism with the following dimensions:

Parameter

Value

Width (cross-wind)

30 m

Depth (along-wind)

45 m

Height

\(H\) = 180 m

Wind direction

0° (wind perpendicular to the 30 m face)

The simulation uses the validated ABL profile from the standalone ABL case as the inlet condition. No modifications to the terrain category, roughness fins, or inlet CSV are needed - the ABL configuration is reused directly.

The primary outputs are:

  • Mean pressure coefficient \(C_p = (p - p_\infty) / (0.5 \rho U_H^2)\) on all facade faces, where \(U_H\) is the mean wind speed at building height.

  • RMS pressure coefficient \(C_{p,\text{rms}}\) as a measure of load fluctuation.

  • Surface pressure colormaps at three height levels: \(z/H = 1/4\), \(2/4\), \(3/4\).

Prerequisites

Before setting up this case you must have a completed and validated ABL case for the same terrain category. Refer to ABL (Atmospheric Boundary Layer) and confirm:

  1. The mean velocity profile at the intended building location matches the target logarithmic profile within ±5%.

  2. The turbulence intensity and TKE profiles are consistent with the target terrain category.

  3. You have retained the inlet profile CSV and the roughness fin configuration from that run - they are imported directly into this case.

Setting Up the Case in AeroSim

Import the Geometry

Import the CAARC geometry (or your building model) as a closed, watertight surface mesh. The building base should be positioned at the floor of the domain, centred in the lateral direction.

Todo

Add UI steps for importing the building geometry, orienting it to the wind direction, and confirming placement within the domain. Include screenshots.

Boundary Conditions

The boundary conditions are identical to the validated ABL case:

  • Inlet: Synthetic Eddy Method (SEM) using the same profile CSV (columns: z, Ux, Rxx, Ryy, Rzz, Rxz, Rxy, Ryz).

  • Ground: IBM EqLog wall model with the same roughness length \(z_0\) and roughness fins at the terrain category fin height.

  • Top and lateral faces: Free-slip Neumann condition (RegularizedNeumannSlip).

  • Outlet: Zero-gradient Neumann condition (RegularizedNeumannOutlet).

  • Building surfaces: IBM with a smooth-wall condition (building facades are hydraulically smooth).

Todo

Add UI steps for assigning boundary conditions and confirming that the imported ABL settings carry over correctly. Include screenshots of the BC panel.

Refinement Box

Add a body refinement box around the building to capture the pressure gradients on the facade and the near-wake. The refinement region should extend at least \(0.5H\) upstream of the building face, \(1H\) downstream of the leeward face, and \(0.5H\) outward from the side and top faces.

Todo

Add UI steps for configuring the refinement box and selecting refinement levels. Include screenshots of the mesh refinement panel.

Domain Guidelines

Todo

Write the internal guidelines for domain sizing for the CAARC case: upstream fetch (multiple of H), downstream length, domain height, lateral width, blockage ratio limit.

Refinement Guidelines

Todo

Write the internal guidelines for mesh refinement for the CAARC case: minimum cell size on the building facade, number of refinement levels, cell count in the body refinement box, total node count, and expected GPU memory budget.

Exports

Todo

Describe what to export from the CAARC case: surface pressure fields, Cp time series at facade probe points, convergence history. Mention any AeroSim export presets for building pressure cases.

Post-Processing and Visualizing Results

Mean Pressure Coefficient

Compute \(C_p\) at each surface point using the mean pressure \(\bar{p}\) and the reference dynamic pressure at building height \(H\):

\[ C_p = \frac{\bar{p} - p_\infty}{0.5 \, \rho \, U_H^2} \]

Plot \(C_p\) as a colormap on the four facade faces. The windward face should show uniformly positive \(C_p\) (typically 0.7–0.9 at the stagnation region), the leeward face uniformly negative \(C_p\) (approximately −0.5 to −0.6), and the side faces a suction peak near the leading edges transitioning to moderate suction.

RMS Pressure Coefficient

The RMS pressure coefficient \(C_{p,\text{rms}} = \sigma_p / (0.5 \, \rho \, U_H^2)\) quantifies load variability. High values on the side faces near the separation lines indicate regions where cladding fatigue may govern design.

Profile Plots

Extract \(C_p\) versus \(z/H\) at the centreline of the windward and leeward faces and compare against the CAARC experimental reference (Melbourne 1980; Obasaju 1992). The AeroSim validation results for the CAARC benchmark are available at docs.aerosim.io/validation.

Todo

Add AeroSim-specific instructions for generating surface pressure colormaps and extracting Cp profiles in the post-processing interface. Include screenshots of the result panel.

Dynamic wind loads, structural accelerations, and spectrum-based analyses (for serviceability and fatigue checks) are covered in a separate advanced guide.

Next Steps