Loads on bodies in wakes.
Loads on bodies in wakes resulting from crossflow at submerged body or from wake translation over submerged body, noting dynamic instability
AERODYNAMIC LOAD↗
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Results for “WAKEFULNESS”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Recent NASA Wake Surfing Flight Research
This paper contains information about the potential benefits and drawbacks of aircraft wake surfing. Wake surfing benefits have been measured and published previously; this paper presents the first known results obtained using a civilian business jet and an ADS-B data link.
wake surfing↗
The D8 Aircraft: An Aerodynamics Study of Boundary Layer and Wake Ingestion Benefit
Goal: Quantify benefits of BLI (Boundary Layer Ingesting) and wake ingestion for the D8. Approach: Overset CFD (Computational Fluid Dynamics) using CGT (Chimera Grid Tools software package) and Overflow-‐2; CFD validation; NASA LaRC (Langley Research Center) 14x22 WT (wind tunnel) data for a 1:11 scale model; Quantifying the BLI and wake ingestion benefit - Direct Comparison between: Efficient conventional (podded nacelle) configuration; BLI (integrated nacelle) configuration.
D8↗
Application of PLIF to Investigate the Hypersonic Wake of a LOFTID-Relevant Model at Mach 10
An experimental investigation of hypersonic wake flows using the planar laser-induced fluorescence (PLIF) measurement technique is summarized in this report. Off-body measurements, primarily flow visualization and velocity, were obtained for the wake of a blunt body model relevant for terrestrial re-entry and Martian entry applications within a Mach 10 hypersonic flow. The design of the model was based on the forebody aeroshell used for the LOFTID (Low-Earth Orbit Flight Test of an Inflatable Decelerator) flight vehicle. This document serves to document the experimental conditions and provide an initial analysis of select test conditions.
PLIF↗
Plasma Wakes from the Baffle Scanning Mechanism on a LEO Mass Spectrometer
The Modular Spectrometer for Atmosphere and Ionosphere Characterization (MoSAIC) is a Quadrupole Mass Spectrometer (QMS) which will fly on NASA's Geospace Dynamics Constellation (GDC) mission in low Earth orbit (LEO), providing measurements of neutral and ionized gas density, temperature, composition, and wind/drift. MoSAIC includes a Baffle Scanning Mechanism (BSM) which periodically sweeps in front of the QMS aperture, enabling determination of the ion temperature and cross-track velocity. Accurate knowledge of the plasma wake formed by the BSM is critical for accurate determination of these quantities. We conduct particle-in-cell (PIC) simulations modeling the interactions between the baffle and plasma across the full range of ion densities, temperatures, and flow speeds GDC is expected to encounter. We discuss the wake physics and present an empirical model which can be implemented in the MoSAIC data analysis process to determine the relevant ion quantities.
mass spectrometer↗
The American WAKE experimeNt (AWAKEN): Groundbreaking International Field Research Addresses Wind Farm Atmosphere Interactions
To help provide that understanding, the U.S. Department of Energy's (DOE's) Wind Energy Technologies Office (WETO) funds the American WAKE experimeNt (AWAKEN). AWAKEN is an international, multi-institutional wind energy field campaign designed to answer the most pressing science questions about the impacts of wind turbine wake effects. From 2022 to 2024, AWAKEN will gather observational data about the atmosphere around and within operational wind farms, validate wind farm models, and advance understanding of wind farm behavior.
AWAKEN↗
Combining shallow-water and analytical wake models for tidal array micro-siting
For tidal-stream energy to become a competitive renewable energy source, clustering multiple turbines into arrays is paramount. Array optimisation is thus critical for achieving maximum power performance and reducing cost of energy. However, ascertaining an optimal array layout is a complex problem, subject to specific site hydrodynamics and multiple inter-disciplinary constraints. In this work, we present a novel optimisation approach that combines an analytical-based wake model, FLORIS, with an ocean model, Thetis. The approach is demonstrated through applications of increasing complexity. By utilising the method of analytical wake superposition, the addition or alteration of turbine position does not require re-calculation of the entire flow field, thus allowing the use of simple heuristic techniques to perform optimisation at a fraction of the computational cost of more sophisticated methods. Using a custom condition-based placement algorithm, this methodology is applied to the Pentland Firth for arrays with turbines of 3.05 m/s rated speed, demonstrating practical implications whilst considering the temporal variability of the tide. For a 24-turbine array case, micro-siting using this technique delivered an array 15.8% more productive on average than a staggered layout, despite flow speeds regularly exceeding the rated value. Performance was evaluated through assessment of the optimised layout within the ocean model that treats turbines through a discrete turbine representation. Used iteratively, this methodology could deliver improved array configurations in a manner that accounts for local hydrodynamic effects.
16 TIDAL AND WAVE POWER↗
High Supersaturation in the Wake of Falling Hydrometeors: Implications for Cloud Invigoration and Ice Nucleation
Aerosol particles, cloud droplets, and ice crystals, coupled through the supersaturation field, play an important role in the buoyancy and life cycle of convective clouds. This letter reports laboratory observations of copious cloud droplets and ice crystals formed in the wake of a warm, falling water drop, which is a laboratory surrogate for a relatively warm hydrometeor in atmospheric clouds, such as a graupel particle in the wet growth regime. Aerosols were activated in the regions of very high supersaturation due to mixing in the wake. A mechanism is explored for attaining very high supersaturations capable of activating significant fractions of the interstitial aerosols within the lifetime of a convective cloud. The latent heat released from the activation of interstitial aerosols and subsequent growth may provide an additional source of buoyancy for cloud invigoration and may lead to larger concentrations of ice crystals.
54 ENVIRONMENTAL SCIENCES↗
Observing the onset of the accretion wake in Vela X-1
High-mass X-ray binaries (HMXBs) offer a unique opportunity to investigate accretion onto compact objects and the wind structure in massive stars. A key source for such studies is the bright neutron star HMXB Vela X-1 whose convenient physical and orbital parameters facilitate analyses and in particular enable studies of the wind structure in HMXBs. Here, we analyse simultaneous XMM-Newton and NuSTAR observations at $\phi_{orb}$ ≈ 0.36–0.52 and perform time-resolved spectral analysis down to the pulse period of the neutron star based on our previous NuSTAR-only results. For the first time, we are able to trace the onset of the wakes in a broad 0.5–78 keV range with a high-time resolution of ~283 s and compare our results with theoretical predictions. Here we observed a clear rise in the absorption column density of the stellar wind N H,1 starting at orbital phase ~0.44, corresponding to the wake structure entering our line of sight towards the neutron star, together with local extrema throughout the observation, which are possibly associated with clumps or other structures in the wind. Periods of high absorption reveal the presence of multiple fluorescent emission lines of highly ionised species, mainly in the soft-X-ray band between 0.5 and 4 keV, indicating photoionisation of the wind.
79 ASTRONOMY AND ASTROPHYSICS↗
Experimental investigation of turbulent wake flows in a helically wrapped rod bundle in presence of localized blockages
In nuclear sodium fast reactors, bundles of rods are tightly packed into a triangular lattice, enclosed in a hexagonal duct, and each pin is spirally wrapped with a thin wire. Flow blockages can potentially impact the local flow characteristics and heat transfer mechanisms in the bundle due to its small subchannel size. The effects of the blockage on the flow structures and heat transfer mechanisms are important aspects that require an accurate investigation. In this study, the flow-field characteristics in the vicinity of a blockage located in the exterior subchannel of rod bundles with helically wrapped wires were experimentally investigated. The velocity fields in the exterior subchannel were acquired by applying matched-index-of-refraction and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of Re 1 = 4000 and Re 2 = 17 000, i.e., equivalent to Rew 1 = 19 600 and Rew 2 = 83 200, respectively, based on the blockage width. The results from the TR-PIV measurements revealed an arch-shaped vortex with a large flow recirculation and a pair of counter-rotating vortices in the wake region downstream of the blockage, which is commonly observed in the wake flow of bluff bodies. The relative lateral distance and angle between the two vortices decreased when the Reynolds numbers increased. Profiles of maximum turbulence intensity along the shear layers illustrated the transition process including the growth, peak, and decay along the flow direction. From the spectral analysis of the turbulent velocities extracted at points along the shear layer, the Strouhal numbers ( St ) representing the vortex shedding frequency were found to be St = 0.25 and St = 0.56 for the left and right shear layers, respectively. Characteristics of shear layers generated by the blockage in the exterior subchannel were investigated via the two-point cross correlation of fluctuating velocities. The patiotemporal cross correlations of turbulent velocities, computed at points in the region where the left shear layer exhibited rolling effects and vortex breakdowns, were considerably wider and longer. The convection velocity U c was estimated to be ~0.82 U m to 0.93 U m . Proper orthogonal decomposition (POD) analysis was applied to the instantaneous velocity fields to extract the statistically dominant flow structures. It was found that POD modes 2–3 and 4–5 formed the pair modes when the corresponding POD temporal coefficients depicted sinusoidal shapes and exhibited nearly circular orbits in the phase space. Spectral analysis of the POD temporal coefficients confirmed the vortex shedding frequencies detected in the analysis of turbulent velocities.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
Fluid structure interaction of a subaqueous pendulum: Analyzing the effect of wake correction via large eddy simulations
The dynamic behavior of a subaqueous cylindrical pendulum and corresponding flow dynamics are investigated. The objectives were twofold: (i) to examine whether the two-dimensional model equations sufficiently capture the three-dimensional dynamics and (ii) to investigate the emerging three-dimensional vortical flow structures. Large eddy simulations with two-way coupling fluid structure interaction were carried out using the immersed boundary method to simulate the motion of the pendulum and its interactions with the initially stagnant water. The resulting pendulum motion is compared against measured data obtained in a series of experimental tests to validate the simulation results and the model equations with and without wake corrections. An analysis of the flow vorticity revealed the development of a vortex ring during the first swing and the formation of tip vortices. The evolution of the vortex rings emerging from the motion of the subaqueous cylindrical pendulum was visualized using Q-criteria showing a reasonable agreement with vortical structures observed in the experiment using particle imaging velocimetry. The hydrodynamic moments acting on the simulated pendulum and the moments calculated from the model equations are analyzed. Using the insights from these numerical simulations, a modification of the wake correction is proposed to enhance the accuracy of the rate of decay and period. The transient effect of coherent flow on pendulum dynamics, especially the added mass effect, is discussed.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Planar turbulent wakes under pressure gradient: Integral and self-similarity analyses
By using a combination of integral and self-similarity analyses, the generalized analytical solutions for the mean transverse velocity and Reynolds shear stress are rigorously derived for the first time for the far field of planar turbulent wakes under arbitrary pressure gradients. Specifically, by assuming self-similarity for the mean axial velocity, the analytical formulation for the mean transverse velocity is obtained from the integral of the mean continuity equation, and the analytical formulation for the Reynolds shear stress is obtained from the integral of the momentum equation. The generalized analytical formulations for the mean transverse velocity and Reynolds shear stress consist of multiple components, each with its unique scale and physical mechanism. In the zero pressure gradient limit, the generalized formulations recover the single-scale equations reported by Wei, Liu, and Livescu. Furthermore, simpler approximate formulations for the mean transverse velocity and Reynolds shear stress are also obtained, and show excellent agreement with the experimental measurements. Here, the findings provide new insights into the properties of planar turbulent wakes under pressure gradients, filling some long-standing gaps in the existing literature.
42 ENGINEERING↗
Debris-induced consequences on turbulence and vorticity in solar photovoltaic module-generated array wakes
Particle-laden flows in solar photovoltaic (PV) systems are inevitable, where wind-swept debris in open environments are carried by high winds and turbulence, coating panel surfaces or damaging structures. Particle deposition, or soiling, is a well-known issue for large-scale plants which rely on uninhibited solar rays for optimal production. But understanding the mechanisms leading to soiling requires a physical and fluid dynamics-centered focus, since turbulence dominates PV panel wakes and is also known to alter particle concentration and trajectories. This study presents an experimental campaign toward consequences of particle-laden flow between two model PV panels using time-resolved particle image velocimetry. The model array was subjected to varied particle volume fractions, including a tracer particle case and a water droplet case. Characterization of mean velocity, turbulence statistics, and mean kinetic energy within the single phase and, separately, particle phase flows showed modified features due to particle inertia. Images captured at a frequency of 1 kHz in the near wake of the upstream panel allow for a first experimental look at vorticity and convective velocity of vortex structures for single-phase and particle-phase flows which are crucial to debris transport and soiling in PV environments.
Energy & Fuels↗
Thermal Weibel instability induced magnetic fields co-exist with linear wakes in laser-ionized plasmas
When a moderately intense, few-picosecond-long laser pulse ionizes gas to produce an underdense plasma column, a linear relativistic plasma wave or wake can be excited by the self-modulation instability that may prove useful for multi-bunch acceleration of externally injected electrons or positrons to high energies in a short distance. At the same time, due to the anisotropic temperature distributions of the ionized plasma electrons, the Weibel instability can self-generate magnetic fields throughout such a plasma on a few picoseconds timescale that can persist even longer than the lifetime of the wake. In the present paper, we first show using simulations that both these effects do indeed co-exist in space and time in the plasma. Using our simulations, we make preliminary estimates of the contribution to the transverse emittance growth of an externally injected beam due to the Weibel magnetic fields in a few-millimeter-long plasma. We then present the results of an experiment that has allowed us to measure the spatiotemporal evolution of the magnetic fields using an ultrashort relativistic electron probe beam. Both the topology and the lifetime of the Weibel instability induced magnetic fields in the experiment are in reasonable agreement with the fields induced by the Weibel instability in the simulations.
43 PARTICLE ACCELERATORS↗
FLORIS v3.5 Wake Modeling and Wind Farm Controls Software [SWR-17-43 and SWR-14-20]
FLORIS is a controls-focused wind farm simulation software incorporating steady-state engineering wake models into a performance-focused Python framework. It has been in active development at NREL since 2013 and the latest release is FLORIS v3.5.Online documentation is available at https://nrel.github.io/floris. The software is in active development and engagement with the development team is highly encouraged. If you are interested in using FLORIS to conduct studies of a wind farm or extending FLORIS to include your own wake model, please join the conversation in GitHub Discussions! https://www.nrel.gov/wind/floris.html
Fleming, Paul↗
Updates on the Wake Potential Calculations for the Electron-ion Collider with ECHO3D
ECHO3D has been used for calculating the geometric impedance and short-range wakefields for several EIC (Electron-Ion Collider) beamline vacuum components in the past few years. This note summarizes the wake potential calculations conducted in 2023 with ECHO3D for components from both the hadron storage ring (HSR) and the electron storage ring (ESR). For the HSR, calculations have been carried out for the polarimeter, the beam screen with pump slots and the bellow with pump ports. For the ESR, the short-range wake potential for the flange weld as well as various designs of the storage ring cavity have been calculated.
43 PARTICLE ACCELERATORS↗
American WAKE Experiment (AWAKEN) Field Campaign Report
The American WAKE experimeNt (AWAKEN) was a large-scale, international collaborative field campaign funded primarily by the U.S. Department of Energy (DOE) Wind Energy Technologies Office. Its main purpose was to gather detailed observations of wind farm-atmosphere interactions to improve understanding of wind farm physics, validate and improve simulation tools, lower uncertainties in wind farm modeling, understand environmental impacts, and ultimately reduce the cost and increase the reliability of wind energy systems. The campaign specifically focused on seven testable hypotheses that include characterizing wind turbine and wind farm wake effects, wind farm blockage, turbulent mixing, structural loading impacts, local environmental impacts, and testing wind farm control technologies. AWAKEN was a highly collaborative effort involving numerous agencies, including: DOE, through the Wind Energy Technologies Office and the Office of Science Atmospheric Radiation Measurement (ARM) User Facility, the U.S. Department of Commerce through the National Oceanic and Atmospheric Administration, many American universities, and internationally funded collaborators from Germany and Brazil.
17 WIND ENERGY↗
Hypersonic Wake Velocity Measurements Using Acetone Molecular Tagging Velocimetry
A non-intrusive laser diagnostic known as molecular tagging velocimetry was used to find quantitative off-body velocity measurements in the wake of a sphere in the Mach 7 Ludwieg Tube Wind Tunnel located at The University of Texas at San Antonio. Acetone gas seeded in the flow was excited using the 4th harmonic of a pulse-burst Nd:YAG laser. The experimental results were used to validate and compare to simulations using a continuous Galerkin flow solver. Both the experimental and simulated results agreed on negative velocities in the viscous shear layer. Near the centerline of the sphere, average velocities of -200 m/s were observed due to reverse flow in the recirculation region. Outside of the shear layer, velocities of 800 m/s were observed in both the experimental and simulated results. The overall average uncertainty for the strut-mounted and free-flight case was estimated to be ±27 m/s. The flow features of the wake were visualized using schlieren imaging, and the experimental results agreed well with the simulated results.
Shoemake, Lawton↗