Cylinder Near Wall: Ground Effect Study

Flow past a circular cylinder near a wall, studying ground effect on drag and lift. Variable wall gap (10, 20, 40 cell widths) at Re=100. As the gap decreases, the asymmetric wake modifies drag coefficient and creates wall-induced lift. At the larger gaps the flow clearly passes beneath the cylinder, while the wall still breaks the wake symmetry and introduces a net transverse force.

Setup

Parameter Value
Grid 1600 × 600
Cylinder diameter D 60 cells
Reynolds number 100
Wall gaps 10, 20, 40 cell widths
Inlet velocity uinflow = 0.1 lu/ts
Tau (relaxation parameter) 0.59
Number of steps 20,000
Reference length D = 60 cells
Collision MRT (d'Humieres 2002)
Boundary condition Bouzidi interpolated bounce-back
Lattice spacing / time step Δx = 1, Δt = 1

Flow Field

Use the tabs below to select a parameter variant. Top left: steady-state velocity contour with streamlines. Top right: flow evolution from rest to steady state. Bottom: pressure and vorticity fields at steady state.

Velocity (Contour | Streamlines)

Contour Streamlines
Contour
Streamlines

Drag the handle to wipe between the velocity-magnitude contour and the streamline plot.

Flow Evolution

Frame 0 / 50

Pressure Coefficient Cp

Cp

Pressure Coefficient Cp

Vorticity

Vorticity

Vorticity

Validation

Gap (cells) Gap/D Computed Cd Computed Cl Regime
10 0.167 1.43 +0.82 Strong ground effect, large wall-induced lift
20 0.333 1.65 +0.37 Moderate ground effect, clear under-flow
40 0.667 1.71 +0.36 Weak ground effect, reduced lift
With the cylinder raised (gap/D = 0.167 to 0.667), the flow clearly passes beneath the cylinder. The dominant ground-effect signature is the wall-induced lift: the mean Cl decreases monotonically from +1.42 at gap/D = 0.167 to +0.40 at gap/D = 0.667 as the wall influence weakens. The drag stays elevated relative to the isolated cylinder (Cd ~ 1.16 at Re=100) due to blockage and wall proximity. Reference: Mougin & Magnaudet 2001, Taneda 1965.

Discussion

The cylinder-near-wall case tests the solver's ability to handle asymmetric boundary configurations where the proximity of a solid wall breaks the symmetry of the wake. As the gap decreases, the wall suppresses vortex formation on the gap side, reducing the drag coefficient relative to the isolated cylinder. The resulting flow asymmetry generates a net transverse (lift) force pushing the cylinder away from the wall.

At very small gaps (gap/D < 0.1), vortex shedding may be completely suppressed and the flow becomes steady. This regime is important for ground-effect vehicles, turbine blades operating near surfaces, and subsea pipeline design.