Competitive Aerodynamics for One of the Fastest Hand-Cycles Ever Built
Client: University of Liverpool Velocipede (ULV) Team
Sector: Aerodynamics / Sports Engineering
Challenge
The University of Liverpool Velocipede Team (ULV) embarked on Arion8, a next-generation hand-powered racing bike targeting new world records at the World Human Powered Speed Challenge (WHPSC) 2025. ULV has a proven pedigree in this category, holding the current male and female hand-cycle world speed records of 51.58 mph (83.02 km/h) and 46.54 mph (74.88 km/h) respectively, set in 2018 with their Arion4 vehicle.
The project was constrained by a tightly defined external envelope to meet rider ergonomic needs, safety rules, and critical transport limitations. Given the limited time and geometry freedoms, much of the vehicle was effectively locked down by early design requirements and keep-out zones (similar to those in motorsport). The rear tail section stood out as the best remaining opportunity to reduce overall aerodynamic drag before finalising the design.
Solution
As both a technical sponsor and aerodynamic partner, Navier supported the Arion8 project through adjoint-based CFD shape optimisation—a method that evaluates how local surface modifications influence total drag via sensitivity gradients.
Given the highly constrained geometry, the optimisation effort focused on the tail region, where meaningful gains could still be achieved. The process guided the design toward a Kamm tail configuration, a classic solution for streamlined bodies that need to balance drag reduction with compact form factors.
In addition to lowering overall drag, the refined geometry improved flow diffusion beneath the tail, smoothing the wake and reducing the risk of concentrated low-pressure zones behind the rear wheel assembly. This was achieved while keeping wetted area growth to a minimum—critical given that viscous drag contributed nearly 50% of the total.
Outcomes
- Achieved a ~10% reduction in total drag, despite tight space and geometry constraints.
- Refined the tail shape to minimise both pressure and viscous drag contributions, without adding significant surface area.
- Provided insight into boundary layer development and flow transition.
- Enabled the Arion8 team to integrate the improvement late in the programme thanks to the modular nature of the modification.
For more on Navier’s expertise in aerodynamics, see our Aerodynamic CFD services.