arXiv subjects

Scott A. Bollt

Publications and source records attributed to Scott A. Bollt.

3 recordsLinked to original sources

arXiv2025

RapidPIV: Full Flow-Field kHz PIV for Real-Time Display and Control

We present a novel architecture for accelerating PIV calculations. An optical flow hardware accelerator does the brunt of the work, with cross-correlation only providing quick corrections. The result is RapidPIV: a free-to-download software program for real-time particle image velocimetry (PIV) for Linux and Windows computers with an Nvidia Turing-gen (or newer) GPU (RapidPIV download at https://rapidpiv.caltech.edu). Dense vector fields and vorticity can be displayed in real time when connected to compatible camera. Processing pre-existing PIV image files is also supported. We achieve 1,150 frames-per-second on 1 megapixel images. Accuracy, repeatability, and robustness are tested with physical experiments involving an accelerated flat plate and a cylinder wake. RapidPIV's accuracy, precision and ability to handle high displacement, velocity gradients, out-of-plane motion, and low seeding density compare favorably with the trusted multi-grid correlation software. However, RapidPIV is a thousand times faster.

physics.flu-dyn↗

arXiv2025

Tailwind turbulence: a bound on the energy available from turbulence for transit, tested in Kraichnan's model

We investigate the unconstrained minimum energy required for vehicles to move through turbulence. We restrict our study to vehicles that interact with their environment through thrust, weight and drag forces, such as rotorcraft or submersibles. For such vehicles, theory predicts an optimum ratio between vehicle velocity and a characteristic velocity of the turbulence. The energy required for transit can be substantially smaller than what is required to move through quiescent fluid. We describe a simple picture for how a flight trajectory could preferentially put vehicles in tailwinds rather than headwinds, predicated on the organization of turbulence around vortices. This leads to an analytical parameter-free lower bound on the energy required to traverse a turbulent flow. We test this bound by computationally optimizing trajectories in Kraichnan's model of turbulence, and find that the energy required by point-models of vehicles is slightly larger than but close to our bound. Finally, we predict the existence of an optimum level of turbulence for which power is minimized, so that turbulence can be both too strong or too weak to be useful. This work strengthens previous findings that environmental turbulence can always reduce energy use. Thus, favorable trajectories are available to maneuverable vehicles if they have sufficient knowledge of the flow and computational resources for path planning.

physics.flu-dyn↗

arXiv2021

How to Extract Energy from Turbulence in Flight by Fast Tracking

We analyze a way to make flight vehicles harvest energy from homogeneous turbulence by fast tracking in the way that falling inertial particles do. Mean airspeed increases relative to flight through quiescent fluid when turbulent eddies sweep particles and vehicles along in a productive way. Once swept, inertia tends to carry a vehicle into tailwinds more often than headwinds. We introduce a forcing that rescales the effective inertia of rotorcraft in computer simulations. Given a certain thrust and effective inertia, we find that flight energy consumption can be calculated from measurements of mean particle settling velocities and acceleration variances alone, without need for other information. In calculations using a turbulence model, we optimize the balance between the work performed to generate the forcing and the advantages induced by fast tracking. The results show net energy reductions of up to about 10% relative to flight through quiescent fluid and mean velocities up to 40% higher. The forcing expands the range of conditions under which fast tracking operates by a factor of about ten. We discuss how the mechanism can operate for any vehicle, how it may be even more effective in real turbulence and for fixed-wing aircraft, and how modifications might yield yet greater performance.

physics.flu-dyn↗