EROCFTAC DATA :

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The diameter of the stilts on which the body was mounted was 30 mm. These extended into the floor of the tunnel, leaving a distance of 50 mm between the ground and the Ahmed body.

Two slant angles for the rear part of the body are reported here: 25o and 35o. In both cases, the length of the slanting section was the same (222 mm). These angles were chosen to be either side of the critical angle of 30o at which separated flow occurs within the wake of the slant.

The geometry of the front curved section of the body is available in ahmed-front-geo.dat.

Flow Parameters

• Kinematic viscosity of air: 15×10−615×10−6 m2/s
• Bulk velocity: Ub=40Ub=40 m/s
• Height of body: h=288h=288 mm
• Reynolds number based on height of body: Re=768,000Re=768,000

Measurement Technique

The experiments were performed in the LSTM low speed wind tunnel. The studies were conducted in a 3/4 open test section (ie. floor, but no sides or ceiling) with a blockage ratio of 4%. The wind tunnel can generate flow velocities from 3 to 55 m/s with average turbulence intensities of less than 0.25%, and all measurements for the Ahmed body were taken at bulk air velocities of 40 m/s. A computer-based feedback system was utilised to ensure constancy of the test section bulk velocity and air temperature.

Hot-wire measurements of the velocity profiles 400 mm upstream of the Ahmed body were obtained to serve as inlet conditions for numerical simulations. These were performed with a two-component hot-wire system, which was rotated to obtain the third component.

Flow visualization using oil streaks was performed for both model shapes. These showed complex three-dimensional flow patterns and confirmed earlier findings that a small change in the slant angle around the critical 30o causes a dramatic change in the flow pattern.

A two-component LDA system was used to make measurements of all three velocity components in the symmetry plane from upstream of the body to some distance downstream behind the closure of the wake. LDA measurements were also made in several transverse planes in the wake.

Available Experimental Data

Measurements available include mean velocity and Reynolds stress profiles on a number of planes, and pressure measurements on the rear part of the body:

• LDA mean velocity and Reynolds stress profiles on a number of planes parallel and normal to the streamwise direction
• Hot wire boundary layer measurements of mean velocity and Reynolds stresses at a number of locations close to the body surface
• Surface pressure coefficients on the rear part of the body

ISSUES to Fix up:

Referring to a published paper:

E.GuilmineauG.B.DengA.LeroyerP.QueuteyM.VisonneauJ.Wackers, “Assessment of hybrid RANS-LES formulations for flow simulation around the Ahmed body”, Computers & Fluids, Volume 176, 15 November 2018, Pages 302-319, https://doi.org/10.1016/j.compfluid.2017.01.005

Used the EROCFTAC DATA to

Represents the flow visualizations such as:

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File available from EROCFTAC DATA

LDA Measurements

LDA measurements of mean velocities, Reynolds stresses and triple moments are available on a number of planes:

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No File available from EROCFTAC DATA.