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Diffuser fences / longitudinal separators

Name: Diffuser fences / longitudinal separators dimension sheet
Creator: Xem Studio
License: https://creativecommons.org/licenses/by/4.0/

Why do diffusers have vertical fences (strakes)? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio

Also called: diffuser fences, diffuser strakes, diffuser separators, diffuser fins, underbody strakes, diffuser vanes, diffuser dividers, rear diffuser fins, diffuser vortex, strakes under car

Exact dimensions. True size, with no printing tolerance added.

sizes: 4 in table

Notes

Diffuser fences are vertical plates running fore-aft in the diffuser. Diffuser downforce depends on vortices formed at its edges near the inlet, which move inboard and upward downstream (Mahon, Zhang & Gage); fences organise that flow.
On the Cranfield DrivAer model, separators at 5 deg and 100 mm spacing in a 10 deg diffuser trimmed front downforce by ~0.03 CL, improved balance at low ride height and cost only 3-5 drag counts (SAE 2018-01-0725).
The file is a reference example built by Xem Studio from the numbers above (Fence spacing 100 mm per Cranfield test (35% model).). Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

Diffuser fences / longitudinal separators size chart

parameter	value or range	source
Separator angle / spacing tested	5 deg, 100 mm spacing in 10 deg diffuser	Cranfield / SAE 2018-01-0725
Front downforce change	dCL about 0.03 lower	Cranfield / SAE 2018-01-0725
Drag penalty	3, 5, 4 counts at h/h0 0.25, 0.50, 0.75	Cranfield / SAE 2018-01-0725
Edge vortex origin	near diffuser inlet	Southampton (Mahon et al.)

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

Cranfield University / SAE	On the Aerodynamics of an Enclosed-Wheel Racing Car (Soares et al., SAE 2018-01-0725)	web	Publisher's page; dimensions are facts
University of Southampton	The Evolution of Edge Vortices Underneath a Diffuser Equipped Bluff Body (Mahon, Zhang & Gage)	web	Publisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

diffuser-fences-strakes-diffuser

Diffuser: 200 mm ramp at 10° behind a flat floor, 300 mm wide, 3 fences

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Plain text: sheet.txt · JSON: /api/geometry?object=diffuser-fences-strakes