What is it about?
We experimentally compare four equal-area base-blowing slots (square, vertical, cross and horizontal) on a square-back blunt-body (Re ≈ 6.5×10⁴), combining force, base-pressure and PIV measurements in wind-tunnel tests. A centred square slot delivers the strongest performance, achieving ≈ 5% drag reduction (and ≈ 12% base-pressure recovery) near the optimal blowing coefficient by lengthening the recirculation region, reducing backflow and mitigating wake asymmetry. Vertical/cross slots are less effective and can reinforce asymmetry at higher blowing rates; the horizontal slot sits in between.
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Why is it important?
For square-back road vehicles (e.g., lorries and vans), a large fraction of total drag comes from the rear wake. Our results provide geometry-level design guidance for robust, low-complexity base-bleed actuators that can be powered passively (stagnation pressure tapping) or by exhaust flow. In practical terms, this approach could help manufacturers cut fuel use and CO₂, without the complexity of high-frequency flow control.
Perspectives
This is an step forward on our research line about drag reduction technologies applied to simplified models of road vehicles.
Manuel Lorite Diez
Universidad de Granada
Read the Original
This page is a summary of: Experimental analysis of the role of base blowing geometry on three-dimensional blunt body wakes, Physics of Fluids, August 2025, American Institute of Physics,
DOI: 10.1063/5.0275586.
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