arXiv subjects

Dev Pradeepkumar Nayak

Publications and source records attributed to Dev Pradeepkumar Nayak.

3 recordsLinked to original sources

arXiv2026

Wing-Rotor Aerodynamic Interactions in Small UAVs During Hover and Cruise

A compact vertical take-off and landing aircraft requires the same tilt-rotor configuration to perform two fundamentally different aerodynamic tasks: sustain hover and deliver efficient cruise. This work investigates the underlying wing-rotor interactions in both operating regimes using a validated unsteady Reynolds-averaged Navier-Stokes equations-based computational framework. For cruise, the advance ratio governs the balance between thrust production, propulsive efficiency, and wake coherence. Lower advance ratios produce a tightly wound slipstream that undergoes strong vortex interactions, leapfrogging, and early wake bifurcation. At higher advance ratios, the slipstream retains a narrower and more coherent jet-like structure, improving propulsive efficiency while reducing both thrust of the propellor and lift of the wing. The flow impingement at the wing is characterized through the approaching, interaction, and convection phases, revealing the combined influence of vortex stretching, wake bifurcation, blockage, image-induced velocity, and streamwise momentum convection on the downstream wake. In hover, the propeller's rotational speed governs the overall aerodynamic performance more strongly than the wing's placement. Although the position of the wing with respect to the propellor modifies the local wake interactions and flow impingement on its leading edge, its influence on the integrated thrust coefficient and figure of merit remains limited. We also explain the vortex and wake dynamics around the propellor and the wing responsible for governing these aerodynamic performance.

physics.flu-dyn↗

arXiv2026

Dynamical Characteristics of the Body-Caudal Fin Joint of a Carangiform Swimmer and its Influence on Hydrodynamics

The hydrodynamics of fish swimming depend on the interaction between the undulation of the body and the flapping of the caudal fin. This study develops a computational framework of a Jackfish-inspired swimmer with an independently mounted caudal fin that pitches passively under fluid forces and a nonlinear torsional spring. The fin synchronizes with the body when damping and stiffness parameters are tuned correctly, producing passive pitching that closely resembles to the displacement of the actively pitching tail. At Re = 3000, synchronized passive pitching generates coherent hairpin and ring vortices that reinforce streamwise momentum and contribute to thrust, whereas larger phase differences lead to wake spread in lateral direction and drag-dominated behavior. These results reveal that nonlinear peduncle mechanics naturally regulate amplitude, phase, and recoil, offering a biologically inspired pathway toward underwater robotic design using passive kinematics.

physics.flu-dyn↗

arXiv2025

Comparative Investigations on Active and Passive Tails of Undulating Swimmers

Fish display remarkable swimming capabilities through the coordinated interaction of the body and caudal fin, yet the potential role of a passively pitching tail in enhancing hydrodynamic performance remains unresolved. In this work, we evaluate the performance of a carangiform swimmer equipped with either an actively pitching tail or a passively pitching tail. Fluid-structure interactions-based simulations are employed to asses how variations in joint stiffness, damping, and inertia influence thrust generation, power demand, and overall stability at two representative Reynolds numbers of 500 and 5000. The results reveal that actively pitching tails tend to generate greater thrust, while passively pitching tails deliver improved outcomes in terms of the power demand at the lower Reynolds number. Larger pitching amplitudes contribute positively only when associated with higher swimming frequency, when produced by reduced inertia for more flexible joints, they lead to unfavorable effects. At the higher Reynolds number, active tails consistently outperform passive ones, although a small subset of passive cases still achieve favorable performance. Across all cases, a recurring balance emerges, with thrust production and power expenditure varying inversely. These findings clarify the hydrodynamic consequences of passive versus active tail motion and establish design principles for bio-inspired underwater vehicles, where smaller swimmers may benefit from passive tail pitching, while larger swimmers are better served by active control

physics.flu-dyn↗