Paper Title
NUMERICAL AND EXPERIMENTAL STUDY ON INTEGRATED VENTILATION DUCT OF HYPERLOOP SYSTEM WITH CIRCULAR & TAPERED GEOMETRY

Abstract
The Hyperloop system, operating within a partially evacuated tube environment, faces significant aerodynamic challenges—particularly the choked-flow phenomenon that arises when the blockage ratio between the pod and the tube approaches the Kantrowitz limit. Ventilation ducts (VDs) integrated into the pod body have emerged as a promising passive strategy to alleviate this drag penalty. This paper presents a combined numerical and experimental investigation into two duct geometries: (i) a uniform circular cross-section duct (inlet and outlet diameter: 300 mm) and (ii) a tapered duct (inlet diameter: 300 mm, outlet diameter: 150 mm, length: 1000 mm), analysed using ANSYS Fluent 2023 with the realizable k-ε turbulence model under compressible, steady-state conditions at pod velocities 30–150 m/s at 0.1 atm. Results demonstrate that the tapered duct achieves up to 30.4% lower pressure drop, a peak outlet velocity of 160 m/s (vs. 48 m/s for circular), and a drag coefficient reduction of 34.5% at Mach 0.9. A scale-model prototype was tested in a subsonic wind tunnel, yielding CFD–experiment agreement within ±8%. Keywords - Hyperloop, Ventilation Duct, Tapered Geometry, CFD, ANSYS Fluent, Drag Reduction, Kantrowitz Limit, k-ε Turbulence Model, Compressible Flow, Blockage Ratio