Wind Deflection Trajectories

This diagram shows how ambient crosswind deflects the buoyant cooking plume away from the hood’s capture zone. Even moderate breezes (5 mph) push the plume centerline most of the way to the edge of the papers’ recommended hood, and winds above 8 mph carry it past the edge for unshielded installations.

Reference readings

Representative values below are computed directly from the same closed-form deflection model (physics/wind.mjs) driving the instrument above — RB-006 §3.1’s δ = 0.35 U_w z / u_0(z) for the papers’ reference source, a medium gas grill, with no side panels; live values update as you move the controls. The table is regenerated by scripts/generate-reference-tables.mjs, never typed by hand. † marks cells where the crosswind Froude number exceeds 2.7, RB-006’s “disrupted” regime, in which the plume loses its coherent column and the linear deflection number is no longer meaningful [RB-006 §3.8, Table 3.8].

At a 30-inch mounting height, a 5 mph crosswind deflects the plume centerline about 11.7 inches (RB-006 Table 3.2b prints 12) — most of the 17-inch overhang RB-002 and RB-005 recommend for a medium gas grill at that height (RB-002 Table 3.6b prints 17, footnoting the exact 16.5) [RB-002 Table 3.6b; RB-005 Table 3.1b, §3.1] — and an 8 mph crosswind deflects it about 18.8 inches (Table 3.2b: 19), past that overhang [RB-006 §3.2]. The same crosswind deflects the plume roughly 1.8× farther at a 48-inch mounting height than at 30 inches (21.1 versus 11.7 inches at 5 mph), because the plume rises farther, and more slowly, before it reaches a higher hood [RB-006 §3.1]. Deflection is linear in wind speed at a fixed height: at 30 inches the 12 mph deflection (28.2 inches) is four times the 3 mph deflection (7.0 inches), and the 3 mph figures at 18, 30 and 48 inches (3.8, 7.0 and 12.7 inches) are the RB-003 benchmark the formula was calibrated against (4, 7 and 12 inches) [RB-006 §3.1].

Key Findings

3 mph is manageable. At light breezes the plume deflects about 7 inches at a 30-inch mounting height — well within the 17-inch recommended overhang.

5 mph is marginal. For the paper’s recommended 57-inch hood over this grill, RB-006 §3.4’s thresholds put the 25%-escape wind at about 4.8 mph and centerline exit at about 7.0 mph (computed from the same physics/capture.mjs identities; RB-006 Table 3.4a v1.1 prints 4.8, 7.0 and 9.3 mph for this row — its v1.0 columns had been evaluated with the wider K = 1.70 hood while labelled with the base-margin overhang, as the paper’s Revision history records). Gusts beyond 5 mph intermittently push the plume outside the hood boundary, producing the gust-correlated smoke escape of FM-4 [RB-006 §4.2; RB-007 §3.5].

8 mph and above cause failure. The roughly 19-inch deflection at 30 inches exceeds the recommended overhang; RB-006 puts unmitigated capture at 45–55% here [RB-006 §4.2]. Side panels or wind baffles become mandatory at this exposure level.

12+ mph is impractical for open hoods. Above 12 mph at cooking height the plume is in RB-006’s disrupted regime (Fr > 2.7 at every standard height by 15 mph). No conventional canopy hood captures this — physical enclosure is required [RB-006 §3.8, §4.2].

Source Papers

• RB-006: Wind Interaction and Crossflow — Deflection model (§3.1), tables (§3.2), critical wind speeds (§3.4), exposure classes (§3.8)
• RB-009: Side Panel Effectiveness — Wind mitigation strategies