High Momentum Research Articles

The role of the in-plane solidity on canopy flows

Turbulent open channel flows developing above submerged canopies made of slender cylinders mounted perpendicular to the channel bed are known to be largely governed by the solidity parameter$\lambda =dh/\Delta S^2$($d$and$h$being the diameter and height of the filament, and$\Delta S$the average spacing between filaments). When the filaments are sufficiently slender, the ratio between the height of the stems and the spacing sets the hydrodynamic regime developing inside and outside the canopy. This ratio also establishes the conditions leading to the transition from a dense to a sparse canopy flow regime (Nepf,Annu. Rev. Fluid Mech., vol. 44, 2012, pp. 123–142). In a previous, companion numerical investigation, Montiet al.(J. Fluid Mech., vol. 891, 2020, A9) used large eddy simulation (LES) to study the influence of the canopy height on the onset of the different regimes without modifying the average spacing$\Delta S$between the stems. In that LES study, we were looking at the complementary situation in which the height of the stems is constant while the filaments’ number density of the canopy is changed. It was found that for low values of$\lambda$(i.e. sparse or moderately dense canopies:$\lambda \lessapprox 0.26$), the flows sharing the value of the solidity obtained by either varying$h$or$\Delta S$are very similar. Differently, for higher values of$\lambda$(i.e. in denser canopies), the effects of$h$and$\Delta S$start to diverge although sharing the same nominal value of$\lambda$. In this paper, we analyse the different physical mechanisms that come into play for dense configurations obtained by varying either$\Delta S$or$h$. In particular, we focus on the most relevant length scales and carry out a detailed analysis of the flows using a triple decomposition approach. We show that the inner region of dense canopy flows, characterised by tall stems, is dominated by wall-normal sweeps delivering high momentum in the wall vicinity. Here, the impenetrability condition of the bed redistributes the available momentum in the wall-parallel directions re-energising an otherwise stagnating flow. Differently, in densely packed canopies, the penetration of the outer jet and the momentum transfer from the external flow are limited by the decreasing value of the wall-parallel permeabilities leading to different behaviours, including a reduction of the total drag offered by the canopy.

Slow complexification

The fact that AdS black hole interior geometries are time-dependent presents two challenges: first, to holographic duality (the boundary matter tends to equilibrate, often very quickly), and, second, to the idea that wormholes can be traversable (the wormhole geometry is dynamic, and the wormhole is apt to collapse too quickly for traversal to be possible). As is well known, the first puzzle can be addressed by considering the quantum circuit complexity of the strongly coupled boundary matter, which can continue to grow long after equilibrium is established. We show that data from a phenomenological model of the Quark-Gluon Plasma indicate the existence of an upper bound on the rate of increase of the (specific) complexity, in agreement with a simple holographic model. We then point out that, in this model, this upper bound becomes stricter if angular momentum is added to the bulk black hole while fixing the temperature (at any value, so the black hole is not near-extremal). We show that the dual phenomenon, a dramatic slowing of the black hole interior dynamics at high specific angular momentum, also occurs. We conjecture that sufficiently slow complexification of the field theories dual to rotating black holes is associated with traversability of the bulk wormhole, when quantum effects are taken into account.

Noise and Jet Momentum of Synthetic Jet Actuators with Different Orifice Configurations

Sound pressure levels and flow characteristics of a synthetic jet actuator (SJA) are investigated experimentally using the following orifice configurations: a) a slender rectangular slot orifice and b) an array of circular orifices with two different orifice diameters. All configurations have similar total orifice neck area, orifice height, and cavity volume, resulting in a similar Helmholtz frequency. Experiments are conducted for orifices mounted on a flat plate under a quiescent condition. The mean jet velocity exhibits resonant peaks at several excitation frequencies, which also gave rise to the sound pressure levels. The resonant frequencies and peak jet velocities were found to depend on the excitation amplitude and orifice configuration. Investigation of the jet momentum penetration into the quiescent air above the different orifice configurations shows that the momentum issuing from the rectangular slot decays much quicker than that of the circular orifices, irrespective of whether the SJA is excited at resonance or not. The most favorable performance (i.e., the highest momentum in the jet core) was obtained with the array of circular orifices having a smaller orifice diameter, even at off-resonance excitations. The work herein shows the possibility of reducing the SJA noise by 8–10 dB by operating the SJA at a frequency away from the Helmholtz frequency while still achieving comparable levels of jet momentum penetration into the crossflow.

Increased clonal hematopoiesis mutational burden and accelerated dynamic evolution of circulating clones in patients with ischemic heart failure

Abstract Background Clonal hematopoiesis (CH) - defined as the age-related acquisition of mutations in hematopoietic stem cells giving rise to mutated circulating leukocytes - is associated with increased risk of death in patients with heart failure with reduced ejection fraction (HFrEF). While the mutational landscape of CH in peripheral blood (PB) of patients with HFrEF is well characterized, the mutational burden in bone marrow (BM) samples of patients with HFrEF as well as its dynamics over time have not been investigated. Methods/Results We analyzed matched BM and PB cells from 68 patients with ischemic HFrEF by deep error-corrected targeted sequencing of 56 CH-driver genes with a detection threshold of VAF ≥0.5%. In PB, 56/68 patients carried at least one CH mutation, whereas 63/68 patients had mutations in BM. The absolute numbers of detectable mutations were significantly higher in BM compared to PB (215 mutations vs 120 mutations; p<0.0001) (Fig. 1A). Likewise, the cumulative VAF was significantly higher in BM compared to PB (3.83 +/- 0.5% vs 3.0% +/-0.7%; mean +/- SEM, p = 0.0025) (Fig. 1B). However, there was a strong correlation between mutation load in PB and BM (r = 0.54, p<0.0001). Among the two most common mutations, DNMT3A mutations were either present in BM only or both compartments (PB only/BM only/ both compartments 2/12/10), whereas TET2 mutations were strikingly enriched in BM cells (PB only/BM only/both compartments 0/16/2). To study the dynamic evolution of CH clones in patients with HFrEF, we serially analyzed PB samples from 19 patients. At baseline, 16/19 patients carried at least one mutation in a CH driver gene and a total of 31 mutations. After a median follow-up of 12 months, 19/19 patients had at least one detectable mutation and a total of 43 mutations were identified (mean number of mutations per patient 1.63 +/- 0.033 vs 2,26 +/- 0.27; mean +/- SEM, p = 0,0410), indicating an increased mutation load over time (Fig. 2A). Moreover, cumulative VAF increased from 1.59 +/-0.36 % to 2.01 +/- 0.38 %). Conclusion Patients with ischemic HFrEF display a high burden of CH mutations compared to values reported for healthy individuals, which is further amplified in the bone marrow compartment. Clones with new mutations arise rapidly in longitudinal samples of patients with HFrEF and clonal expansion occurs with high momentum. The overrepresentation of mutations in the BM is indicative for augmented DNA damage in the hematopoietic stem cells of patients with HFrEF, while the rapid expansion of mutated circulating clones over time suggests that heart failure itself may expedite the expansion of hematopoietic cells harboring CH-driver mutations.

Wind tunnel experimental study of aerodynamic characteristics of co-flow jet wing with built-in air source

To further investigate the aerodynamic characteristics and control mechanisms of co-flow jet wings, this study presents the design of a co-flow jet wing (CFJ-CLARKY18) with an embedded micro centrifugal compressor. The CFJ-CLARKY18 wing, based on the CLARKY18 airfoil, incorporates a miniature centrifugal compressor positioned horizontally within the wing's cavity, with its rotor axis perpendicular to the wing chord line, thus alleviating geometric constraints and the compressor's exhaust swirl. The integration of the co-flow jet device with the wing is achieved through a split-flow channel design to ensure uniform co-flow jet injection, followed by verification of jet uniformity and calibration of six jet momentum coefficients. Subsequently, static and dynamic control experiments of the co-flow jet wing are conducted in an open-return wind tunnel, utilizing force measurement systems and high-speed particle image velocimetry tools to investigate its aerodynamic characteristics and control mechanisms. Static stall tests indicate that, compared to the original wing, the CFJ-CLARKY18 wing exhibits a significant increase in lift and a noticeable delay in stall angle. At low angles of attack, an increase in co-flow jet momentum leads to a reduction in drag coefficient, with the possibility of achieving negative drag (thrust) even at high co-flow jet momentum coefficients. The results of dynamic stall tests with force measurements indicate that, while keeping the reduced frequency constant, an increase in co-flow jet momentum coefficient results in higher maximum lift and average lift coefficients, accompanied by a significant reduction in average drag coefficient and the hysteresis loop area of the lift coefficient. Despite the increased reduced frequency exacerbating the wing's stall effect, the stall effect weakens significantly once the co-flow jet momentum coefficient is increased.

Dynamical studies for the S+ + D2(v0 = 2, j0 = 0) → SD+ + D reaction by time-dependent wave packet

Using time-dependent wave packet method, the dynamics studies of the S+ + D2(v0 = 2, j0 = 0) → SD+ + D reaction were carried out based on the potential energy surface (PES) reported by Zhu et al., (Phys. Chem. Chem. Phys.23 4757–4767 (2021)). The isotope effect is very obvious. When the H atom is replaced by the D atom, the reaction probability at total angular momentum equal to zero has a threshold of about 0.28 eV and it decreases significantly in the collision energy range studied. The total and rovibrational state-resolved integral cross section were reported and the results indicate that the distribution of integral cross section is mainly concentrated in the ground state. The forward biased differential cross sections show that the stripping mechanism due to high total angular momentum plays a dominant role in the reaction.

Dead cone effect in charm and bottom quark jets

The evolution of a heavy quark initiated jet is mainly ruled by gluon bremsstrahlung. As a consequence of the dead-cone effect, this radiation is suppressed in the forward direction at angles smaller than that proportional to the heavy quark mass MQ, i.e. Θ0=MQ/EQ at energy EQ of the primary quark. In this paper, we unveil this effect in charm and bottom quark jets using DELPHI and OPAL data from Z0 boson decays in e+e− annihilation at center of mass energy 91.2 GeV. The analysis of the reconstructed heavy quark fragmentation function in momentum space shows the strong suppression of hadrons at high momenta in such events compared to light quark fragmentation by a factor ≲1/10. The amount of this suppression is well reproduced by perturbative QCD (pQCD) within the Modified Leading Logarithmic Aproximation and the compact scheme of Local Parton Hadron Duality (MLLA-LPHD). As a new result, we obtain an almost perfect agreement between the light quark fragmentation functions expected at W0∝MQ from DELPHI and OPAL data with Pythia8 and shed light on the reasons for the existence of the ultra-soft gluon excess at small momentum fraction in comparison with pQCD predictions.

February, share turnover, and momentum in China

We show that significant momentum exists in China equity returns outside the month of February for both the past return and the 52-week high momentum ranking criteria. For 6-month holding periods, the magnitudes range from 73 bp to 110 bp per month in both raw and factor-adjusted returns using the China factors of Liu et al. (2019). A strong seasonal February reversal masks momentum when all months are considered together. The reversal is associated with a spike in turnover for recent loser stocks, which we attribute to an appetite for lottery-like stocks by retail investors in the season of the Chinese New Year. We show that the turnover difference between winner and loser stocks is a significant determinant of momentum in all three culturally Chinese equity markets—China, Taiwan, and Hong Kong. However, consistent with the dominance of retail investors in China, the February seasonal is weaker in Taiwan and non-existent in Hong Kong, and strong enough to mask momentum in other months only in China.

Superposing and modulating heterogeneous optical vortices of high-order orbital angular momentum

This article reports the preparation of high orbital angular momentum (OAM) using non-uniform beam interference both theoretically and experimentally. This study commences with the reconstruction of Bessel–Gaussian vortex beams utilizing power-exponential-phase vortices. Subsequently, two reconstructed beams are used for interfere, followed by the application of the phase multiplication technique. This methodology enables higher-order operations on the interfered beams, thereby escalating their topological charges and facilitating the attainment of high-orbit angular momentum. The implementation of these methods is especially relevant in the realms of optical manipulation and remote sensing. Lastly, the high OAM optical vortex is subjected to rotation at any controllable angle. This manipulation introduces an additional degree of freedom for particle operations, thereby expanding their application prospects.

Gluon radiation from a classical point particle: recoil effects

The gluon radiation spectrum of a classical particle struck by a sheet of colored glass, is a key ingredient in understanding the distribution of energy and baryon density in the fragmentation region, particularly in the initial stages of heavy ion collisions. However, the currently known classical spectrum has a troublesome high-momentum tail (Kajantie et al. in Phys. Rev. D 100(5):054011, 2019; Phys Rev D 101(5):054012, 2020). By comparing tree-level bremsstrahlung of a spin-less quark to the above-mentioned known result, we propose an interpolating formula that takes into account the recoil of the struck particle, and therefore produces the correct perturbative behaviour at high momentum of the radiated gluon.

The Momentum Battle in an Upper Airway During High Flow Nasal Cannula Oxygen Therapy

Abstract Two types of high flow nasal cannula (HFNC) oxygen therapy were tested using computational models of the human upper airway to investigate cannula geometry's effect on CO2 flush. Models were run with a generic HFNC geometry, two High Velocity Nasal Insufflation (HVNI) cannula geometries, and without any cannula, each for open and closed mouth patient scenarios. For the open mouth scenario, models included either an inflamed left nasal passageway or a healthy (uninflamed) left nasal passageway. With a healthy left nasal passageway and open mouth, the CO2 remaining in the airway at end-exhale was 1.88 mg and 1.84 mg for the HVNI cannulas, 2.56 mg for HFNC, and 10.0 mg for the model with no cannula. With an inflamed left nasal passageway and open mouth, the CO2 remaining was 1.97 mg, 1.95 mg, 4.24 mg, and 10.5 mg for the same sequence of therapy types. For the closed mouth models, the distinction between therapy types was negligible. It was found that the higher momentum from the HVNI cannulas created a higher resistance against the infiltration of exhaled CO2 into the upper airway. The HVNI cannulas also began flushing the airway (reducing total CO2 mass) earlier in the exhalation cycle than both the HFNC and no-cannula models. The higher resistance to expiratory flow entering the upper airway and earlier transition to flush led to HVNI therapy having the lowest values of CO2 remaining in the airway.

The Effect of the Movement in 52-Week High on Momentum Profit: The Evidence from Taiwan

Purpose: This paper aims to examine the impact of price movements in 52-week highs on a 52-week high momentum strategy. This study refers to the upward or downward movement in 52- week highs as an updating effect and determines how this effect influences the profitability of the original 52-week high momentum strategy. Design/methodology/approach: This paper decomposes the ratio of stock price to 52-week high into denoted two components: price change and updating components. We construct two momentum strategies, each focusing on adjusting either the price change or the updating component. Additionally, we employ a portfolio approach and Fama-MacBeth regression analysis to investigate the profitability of each proposed momentum strategy. Findings: The empirical results reveal that removing the price change component (updating component) from the original 52-week high measure can increases (decreases) the momentum profit, implying that the updating component dominates the price change component. Moreover, our analysis shows that when a high ratio of stock price to 52-week high is driven by a downward updating event, the subsequent positive momentum for a winner portfolio is more substantial. Research limitations/implications: This paper investigates the influence of 52-week highs movement on momentum strategies, utilizing data from Taiwan stock market. The findings reveal that accounting for the updating effect of 52-week highs can enhance the profitability of the original momentum strategy. However, it is important to note that this conclusion is currently limited to relatively inefficient stock markets. The impact on relatively efficient markets remains an area that requires further research for a comprehensive understanding. Originality/value: The finance literature widely acknowledges the 52-week high price as a reference point that can impact investors' trading psychology. Numerous empirical studies have confirmed the profitability of the 52-week high momentum investing strategy. However, these studies have not thoroughly explored the implications and effects of price movements within the scope of a 52-week high momentum strategy. Taking behavioral perspectives into account, this paper considers that the updating of 52-week high prices can influence investors' attention and subsequently impact the profitability of the momentum strategy.

A large-momentum-transfer matter-wave interferometer to measure the effect of gravity on positronium

This paper reports the study of a new interferometric configuration to measure the effect of gravity on positronium. A Mach–Zehnder matter-wave interferometer has been designed to operate with single-photon transitions and to transfer high momentum to a 200 eV positronium beam. The work shows the results and methods used to simulate the interferometer and estimate the operating parameters and the time needed to perform the experiment. It has been estimated that within less than 1 year, the acquisition time is sufficient to achieve a 10% accuracy level in measuring positronium gravitational acceleration, even with a poorly collimated beam, which is significant for theoretical models describing matter–antimatter symmetry. These results pave the way for single photon transition large momentum transfer interferometry with fast atomic beams, which is particularly useful for studies with antimatter and unstable atoms.

Spray Flame Characterization of a Dual Injector for Compact Combustion Systems

ABSTRACT The scalability of liquid fuel operated jet stabilized combustion system toward scales and mixing timescales relevant for corresponding micro gas turbine systems is impeded by the lack of suitable injection concepts. The high momentum of the combustion air jet can deteriorate the spray quality of conventional injection systems. In combustors with reduced mixing timescales (e.g. MGT and compact aero-engines) this results in elevated emissions and a prompt primary atomization is essential. For this purpose, a canonical confined jet spray burner is developed and equipped with a novel in-house dual-pressure swirl/airblast injection concept. An extensive parameter variation on the jet bulk velocity (80 , equivalence ratio (0.6 , combustion air preheat temperature (500 (K) 800) and premixing length (0.0 (mm) ≤ 48) is conducted to delineate the operational range. The spray process originating a partially premixed and a direct injection case is characterized by means of phase Doppler interferometry and shadowgraphy. The combustion process is described via OH*-chemiluminescence, flame photographs and exhaust gas measurements. The results show that the developed injection system yields Sauter mean diameters predominantly below 25 μm over the entire parameter range due to robust and prompt primary atomization. Moreover, the primary atomization process of the dual injector is sufficient under all conditions to confine secondary atomization close-to the combustor nozzle exit. The flame stabilization and reaction progress are more sensitive to the air preheat temperature than the bulk jet velocity variation as the mixture homogenization is limited by the vaporization process. Moreover, with decreasing reactivity (i.e. equivalence ratio and preheat temperature) the flame stabilization is increasingly dominated by the recirculated hot exhaust gas, indicating a transition from conventional turbulent flame propagation to auto-ignition influenced reaction progress. The resulting NOx and CO emissions approximate the values measured previously in related methane powered combustion systems. Consequently, the developed injection system is promising to expand the flexibility of compact gas turbines to liquid fuels while maintaining low emissions.

Elucidating the nature of the proton radioactivity and branching ratio on the first proton emitter discovered 53mCo

The observation of a weak proton-emission branch in the decay of the 3174-keV 53mCo isomeric state marked the discovery of proton radioactivity in atomic nuclei in 1970. Here we show, based on the partial half-lives and the decay energies of the possible proton-emission branches, that the exceptionally high angular momentum barriers, {{{{{{mathcal{l}}}}}}}_{{{{{{rm{p}}}}}}}=9 and {{{{{{mathcal{l}}}}}}}_{{{{{{rm{p}}}}}}}=7, play a key role in hindering the proton radioactivity from 53mCo, making them very challenging to observe and calculate. Indeed, experiments had to wait decades for significant advances in accelerator facilities and multi-faceted state-of-the-art decay stations to gain full access to all observables. Combining data taken with the TASISpec decay station at the Accelerator Laboratory of the University of Jyväskylä, Finland, and the ACTAR TPC device on LISE3 at GANIL, France, we measured their branching ratios as bp1 = 1.3(1)% and bp2 = 0.025(4)%. These results were compared to cutting-edge shell-model and barrier penetration calculations. This description reproduces the order of magnitude of the branching ratios and partial half-lives, despite their very small spectroscopic factors.

Long-term stability and perspectives of the ALICE-HMPID detector at LHC during run 3

The ALICE High Momentum Particle IDentification (HMPID) is a Ring Imaging Cherenkov detector that identifies π, k and p in the transverse momentum interval 1 < pT < 5 GeV/c. The HMPID consists of seven proximity focusing RICH modules, 1.3 × 1.3 m2 each. They are based on liquid C6F14 as Cherenkov radiator, and on MWPCs equipped with CsI pad segmented photocathodes as photon detector. During the LHC Long Shutdown 2 (LS2, 2019–2021) the HMPID underwent upgrading activities that increased the event read out rate up to ∼20 kHz, 10 times faster than in Run 2. The performance of the read-out electronics and the MWPCs status after a stop of 4 years, using the first Run 3 data (2022), are presented. The HMPID will also constraint the measurement of the inelastic (anti-)deuteron inelastic cross section in the momentum interval 0.2–2 GeV/c. For such aim during LS2 two aluminium absorbers 1.3 × 1.3 m2, one with a thickness of 8 cm, half interaction length, and the other with a thickness of 4 cm, were installed in front of two RICH modules. Preliminary Monte Carlo results on the expected uncertainties on the cross section measurement are given. Finally, the projection of the CsI photocathodes stability at the end of Run 3 after the absorption of a charge dose ten times higher than in Run 2, is discussed.

A hybrid CPU/GPU method for Hartree-Fock self-consistent-field calculation.

The calculation of two-electron repulsion integrals (ERIs) is a crucial aspect of Hartree-Fock calculations. In computing the ERIs of varying angular momentum, both the central processing unit (CPU) and the graphics processing unit (GPU) have their respective advantages. To accelerate the ERI evaluation and Fock matrix generation, a hybrid CPU/GPU method has been proposed to maximize the computational power of both CPU and GPU while overlapping the CPU and GPU computations. This method employs a task queue where each task corresponds to ERIs with the same angular momentum. The queue begins with ERIs of low angular momentum, which are computationally efficient on GPUs, and ends with ERIs of high angular momentum, which are better suited for CPU computation. CPUs and GPUs dynamically grab and complete tasks from the start and end of the queue using OpenMP dynamic scheduling until all tasks are finished. The hybrid CPU/GPU computation offers the advantage of enabling calculations with arbitrary angular momentum. Test calculations showed that the hybrid CPU/GPU algorithm is more efficient than "GPU-only" when using a single GPU. However, as more GPUs are involved, the advantage diminishes or disappears. The scaling exponents of the hybrid method were slightly higher than "GPU-only," but the pre-exponent factor was significantly lower, making the hybrid method more effective overall.

H i-rich but low star formation galaxies in MaNGA: physical properties and comparison to control samples

ABSTRACT Gas-rich galaxies are typically star forming. We make use of H i-MaNGA, a programme of H i follow-up for the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey of the Sloan Digital Sky Surveys, to construct a sample of unusual neutral hydrogen (H i, 21 cm)-rich galaxies that have low star formation rates (SFRs), using infrared colour from the Wide-field Infrared Survey Explorer as a proxy for specific SFR. Out of a set of 1575 MaNGA galaxies with H i-MaNGA detections, we find that 83 (5 per cent) meet our selection criteria to be H i rich with low SFR. We construct two stellar mass-matched control samples: H i-rich galaxies with typical SFR (high SF control) and H i-poor galaxies with low SFR (low H i control). We investigate the properties of each of these samples, comparing physical parameters such as ionization state maps, stellar and ionized gas velocity and dispersion, environment measures, metallicity, and morphology to search for the reasons why these unusual H i-rich galaxies are not forming stars. We find evidence for recent external accretion of gas in some galaxies (via high counter-rotating fractions), along with some evidence for active galactic nucleus (AGN) feedback (from a high central low-ionization emission-line region and/or red geyser fraction), and bar quenching (via an enhanced strong bar fraction). Some galaxies in the sample are consistent with simply having their H i in a high angular momentum, large-radius, low-density disc. We conclude that no single physical process can explain all H i-rich, low-SFR galaxies.

Designing Vortex Generators for Tidal Turbine Blades

Increasing tidal turbine performance through innovation is crucial if the cost of tidal energy is to become competitive compared to other sources of energy. The present investigation deals with the application of Vortex Generators (VGs) on tidal turbines in view of increasing their performance. The more mature wind energy industry uses passive VGs either as a retrofit or in the blade design process to reduce separation at the inboard part of wind turbine blades. Tidal turbine blades also experience flow separation and here we examine whether passive vane VGs can be used to reduce or suppress that separated flow.&#x0D; Vortex generators (VGs) in various forms have been used and studied for flow separation control on wings since the 1940s [1]. Their working principle is relatively simple: they generate streamwise vortices that energise the boundary layer on the surface they are attached to, by bringing high momentum fluid closer to the surface [2]. This mechanism has been described by various researchers [3–6], while a number of studies have provided optimization guidelines under a variety of flow conditions [7–13].&#x0D; In the present investigation, a VG configuration is selected following a thorough wind tunnel campaign. It is found that sizing parameters for the tidal turbine profile are very similar to the wind turbine relevant literature [13,14]. The best performing vane VG configuration had a height of 0.007c, which corresponded to half the local boundary layer height (0.5δ) for operational Reynolds numbers. The results are also used to validate a Reynolds Averaged Navier Stokes (RANS) VG modelling approach using the BAY model [15]. The validated method is used to simulate the flow past a tidal turbine in both model size (1:8) and full scale, see Figure 1. The results show that VGs do suppress flow separation in both cases. However, and importantly, it is revealed that the significance of rotational effects is such that when deciding VG placement locations, only the full size blade should be considered. In the interest of brevity, the performance increase caused by a standard VG configuration is show in Figure 2, where a power coefficient improvement of 1.05% is predicted at λ=3. Figure 3 shows the effect on the normal and tangential forces on the blade. In the final paper and presentation, the results for different VG locations will be included and analysed in detail.

A computational study of particle dynamics in synthetic jet flow field

This computational study aims to investigate the transport and dispersion of solid particles in a synthetic jet flow field. Solid spherical particles were injected into the jet at a single point, and their behavior was observed until they left the domain. The interaction between the particles and the vortex rings in the jet was compared for synthetic jets, with different Strouhal numbers (0.05, 0.1, and 0.2). The Reynolds number (Re = 150), the mass of injected particles, particle diameter distribution, and particle Stokes number at injection were kept constant. The results showed that the jet's momentum mainly transported the particles, while the vorticity of the vortex rings caused them to spread. The particle Stokes number affected the distribution of particles within the jet, with a higher Stokes number particle concentrating at the jet's center and lower Stokes number particles being carried within the vortex ring. For the low Strouhal number jet, the combined effect of the fast decline in the particle Stokes number, low vorticity of vortex ring, significant distance between successive vortices, and high jet momentum resulted in a higher spread of particles and rapid transport across the domain. As the Strouhal number increased, the particle Stokes number decreased slowly downstream; moreover, the vorticity of the vortex ring increased, the distance between vortices decreased, and low momentum imparted by the jet led to less particle spread and slower transport. Overall, the spread and transport of particles were most effective in the synthetic jet, with the low Strouhal number.