W124 E320 aerodynamic CFD

Project brief

ProblemAssess whether a front bumper change altered modeled drag.

ConstraintA raw vehicle OBJ exceeded one million facets and needed repair before meshing.

My responsibilityI prepared geometry, domain, mesh, Fluent setup, and post-processing.

Project scopeThis project compared two simulated bumper configurations.

Decisions and iterations

Prepare geometry

SpaceClaim shrink-wrapping converted the raw faceted OBJ into a watertight simulation body. Both bumper versions were processed for comparison.

Build comparable domains

A half-car symmetric wind-tunnel domain used approximately 99,000 cells and prism-layer inflation. The inlet was set to 20 m/s.

Solve and inspect flow

Steady-state RANS k-ε results were reviewed with velocity, pressure, and pathline figures. I checked the residual history alongside the flow fields before comparing the cases.

Pressure contour from the modeled comparison

Interpret a near-neutral result

The model predicted a drag difference of only 0.25%. That is too small to distinguish from geometry, mesh, and solver uncertainty, so the two bumper designs performed similarly in this study.

These are CFD predictions. A mesh-sensitivity study and physical measurements would be needed to judge whether such a small difference persists outside this setup.

Technical details

Mesh and boundary conditions

Both versions used a half-car symmetry domain, approximately 99,000 cells, prism inflation, a 20 m/s inlet, standard k–ε RANS, stationary no-slip road/body walls, and a pressure outlet. The report gives a roughly 0.92 m² reference area.

Surface mesh around the vehicle and enclosure before the Fluent solve. Report page 11.

Solver and convergence

Both cases ran 500 iterations. Turbulence, velocity, and momentum residuals converged; continuity stabilized without meeting the strict residual target. That residual behavior matters when judging the small difference between cases.

Residuals over 500 iterations. Continuity levels off above the strict target while the other residuals continue to fall. Report page 15.

Force breakdown

The report gives Cd 0.29271 stock and 0.29199 modified, a relative difference near 0.25%. Its Cl values, −0.02968 and −0.04659, are model predictions. The force tables list 66.21 N stock and 66.30 N modified despite the lower modified Cd. Reference area and half-car normalization need checking before those forces can be compared directly.

Project values and components