A numerical investigation into the thrust characteristics of the RAS-HA-X25 autonomous underwater vehicle through CFD-based simulation

Grm, Aleksander (author), Peljhan, Marko (author), Kamnik, Roman (author), Dobrevski, Matej (author), Majcen, Dominik (author), Androjna, Andrej (author)

The rapid development of Autonomous Underwater Vehicles (AUVs) has increased the demand for propulsion systems that balance thrust density, hydrodynamic efficiency, and acoustic discretion. This study presents a comprehensive numerical investigation of the performance of the Blue Robotics T500 thruster, embedded within the RAS-HA-X25 AUV’s internal conduit. Using transient Computational Fluid Dynamics (CFD) within the OpenFOAM framework, this research assesses the propulsive characteristics of the thruster across six distinct outlet geometries, including convergent jet nozzles and multilobed “daisy” configurations. To improve computational efficiency for parametric design, a calibrated actuator disc model was developed and validated against resolved-rotor simulations, revealing a 15 % discrepancy attributed to tip leakage and hub vortex effects. Results show that at the operational advance ratio (J = 0.167), the 60 mm convergent nozzle is the optimal configuration for maximising thrust, achieving a peak net thrust of 42 N. In contrast, the daisy-type lobed geometries, while causing a 50 % reduction in absolute thrust compared to a standard cylindrical pipe, significantly homogenise the exit-plane velocity distribution and reduce swirl intensity. These findings indicate that lobed terminations provide a viable mechanism for reducing hydroacoustic signatures, offering a strategic “stealth” advantage for low-observable underwater platforms where acoustic discretion is prioritised over pure thrust density. This study establishes a robust methodology for optimising embedded propulsion modules in next-generation autonomous and hybrid underwater vehicles.

• Language: English
• Keywords: propeller, duct, hydrodynamics, BlueRobotics T500 Thruster, outflow nozzle
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FPP - Faculty of Maritime Studies and Transport; FS - Faculty of Mechanical Engineering; FE - Faculty of Electrical Engineering; FRI - Faculty of Computer and Information Science
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: Str. 1-27
• Numbering: Vol. 14, no. 7
• PID: 20.500.12556/RUL-182852
• UDC: 533.662.2:629.014.9
• ISSN on article: 2077-1312
• DOI: 10.3390/jmse14070600
• COBISS.SI-ID: 272915459
• Publication date in RUL: 25.05.2026

Record is a part of a journal

• Title: Journal of marine science and engineering
• Shortened title: J. mar. sci. eng.
• Publisher: Multidisciplinary Digital Publishing Institute
• ISSN: 2077-1312
• COBISS.SI-ID: 523219993

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian

Abstract

Raziskovalni članek obravnava razvoj naprednih pogonskih sistemov za avtonomna podvodna vozila (AUV), ki omogočajo optimalno razmerje med potiskom, učinkovitostjo in nizko zvočno zaznavnostjo. Z uporabo numeričnih simulacij (CFD) so analizirane različne geometrije iztoka, ki vplivajo na zmogljivost in prikritost delovanja. Rezultati kažejo, da določene konfiguracije povečujejo potisk, druge pa pomembno zmanjšujejo akustični podpis vozila. To omogoča razvoj bolj prikritih in učinkovitih podvodnih sistemov. Raziskava neposredno podpira razvoj podvodnih dronov za nadzor, zaščito in varovanje pristanišča Koper. Poleg tega omogoča optimizacijo delovanja v kompleksnih podvodnih okoljih, kjer sta zanesljivost in avtonomija ključnega pomena. Prispeva tudi k večji tehnološki neodvisnosti in konkurenčnosti Slovenije na področju naprednih pomorskih in obrambnih tehnologij.

• Keywords: propeler, obtočni kanal, hidrodinamika, potisnik BlueRobotics T500, iztočna šoba

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: L7-60164-2025
• Name: Trajnostni in digitalni okvir za varnost in zaščito v pristaniščih

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P2-0228-2022
• Name: Analiza in sinteza gibanja pri človeku in stroju