Steady Flow Velocity Research Articles

Decoding burst swimming performance: a scaling perspective on time-to-fatigue.

Fatigue curves quantify fish swimming performance, providing information about the time ([Formula: see text]) fish can swim against a steady flow velocity (Uf) before fatiguing. Such curves represent a key tool for many applications in ecological engineering, especially for fish pass design and management. Despite years of research, though, our current ability to model fatigue curves still lacks theoretical foundations and relies primarily on fitting empirical data, as obtained from time-consuming and costly experiments. In the present article, we address this shortcoming by proposing a theoretical analysis that builds upon concepts of fish hydrodynamics to derive scaling laws linking statistical properties of [Formula: see text] to velocities Uf, pertaining to the so-called burst range. Theoretical arguments, in the present study, suggest that the proposed scaling laws may hold true for all fish species and sizes. A new experimental database obtained from over 800 trials and five small-sized Cypriniformes support theoretical predictions satisfactorily and calls for further experiments on more fish species and sizes to confirm their general validity.

Machinability and mechanism of abrasive flow machining ultra-precision surface with orientated grinding marks

The loud noise in electric automobile caused by the overlap between orientated grinding marks with meshing line on ground gear tooth surface becomes a big problem for both drivers and manufacturers. Relying on the excellent self-deformation features and trace material removal, the abrasive flow machining (AFM) process exhibited potential machinability for above ultra-precision ground surface. Benefiting by the pseudo network structure, the abrasive media would possess both excellent elasticity and fluid capability, which could be quantitatively reflected by storage modulus, loss modulus and shear thinning nature in rheological properties. Meanwhile, deriving from the CFD simulation, the media exhibited the steady flow velocity and shear stress at the finishing channel, potentially contributing to the finishing uniformity on the target ground channel, which was subsequently confirmed by the change of ground surface morphology and profiles at the initial and finished state. Most convex peaks and concave valleys have been effectively subdued and whittled, leading to a rather smoother surfaces than initial ones. Besides, on account of the different collision position between grains with convex peaks, the finishing mechanism on ground surfaces with orientated marks could be elaborated as the transition effect from directly fractured material removal on convex peak cusp into plastic deformation on residual convex peaks. Combining with the interaction between continuous matrix and discrete grains in flow field, the mechanics on single grain was systematically investigated to establish the material removal theoretical model. Generally, the AFM technique exhibited the stunning machinability on ultra-precision ground surface.

Multi-objective optimization of multi-channel cold plate under intermittent pulsating flow by RSM and NSGA-Ⅱ for thermal management of electric vehicle lithium-ion battery pack

The heat transfer and energy consumption characteristics are the most important performance parameters of cold plate for thermal management of electric vehicle lithium-ion battery pack. In this work, in order to address the issue about multi-objective optimization of multi-channel cold plate under intermittent pulsating flow, RSM (Response Surface Methodology) and Non-dominated Sorting Genetic Algorithm II (NSGA-II) is combined to make a trade-off between the average heat transfer coefficient and energy consumption of multi-channel cold plate under intermittent pulsating flow. Box-Behnken design is used to arrange a series of numerical investigations using the steady flow velocity vin, pulsation amplitude A, and pulsation frequency e as design variables and the average heat transfer coefficient have and energy consumption W as objective functions. Regression models are created in the form of quadratic polynomials, and the significance of each term in the model is determined by analysis of variance (ANOVA). Results show that the linear term of vin has the greatest effect on have and W. According to the Pareto optimal solution obtained from NSGA-II, the optimal objective functions are have = 394.7012 W m−2 °C−1, W = 0.1086 J, and the corresponding design variables are vin = 0.02392 m/s, A = 0.1778 and e = 3.1846 Hz.

Establishment of Stability Evaluation Criteria for the Oil-Gas Interface during Gas-Cap Gravity Flooding in Oil Reservoirs with Strong Edge-Water Drive.

A three-dimensional (3D) experimental model considering the influence of water energy is established to innovatively analyze oil-gas interface stability, and it is found that a stable gas cap with sufficient driving energy can be formed only under a stable oil and gas interface. So, the bidirectional displacement through the gas cap and edge water can be realized during the late development stage in the strong edge-water drive reservoirs. Results show that the recovery of bidirectional displacement can reach 60%, while the recovery of an unstable interface is basically below 50%. The recovery degree under a stable oil-gas interface is more than 25.63% than that of the unstable interface. Based on the Navier-Stokes equation, a "steady flow velocity u s" formula that considers the influence of multiple factors is defined, and the ratio of the flow velocity at the oil-gas interface to the gas injection rate is controlled between 0.6 and 0.85 to determine the criteria for the stable oil-gas interface. At the same time, the differentiation-hindered quasi-number (Gr) is defined to clarify the influence mechanism of various mechanical factors on gravity differentiation and the difficulty of oil and gas replacement. When Gr is equal to 1, the oil-gas interface reaches stable migration conditions. Larger formation dip angle, higher permeability, smaller oil viscosity, and lower gas injection rate are the favorable conditions for forming stable flow. The findings are recommended to be used in reservoirs with relatively homogeneous reservoirs, certain dip angles, and moderate or low oil viscosity.

Development of multichord ion Doppler spectroscopy system for toroidal flow measurement of field-reversed configuration.

A double-chord ion Doppler spectroscopy (IDS) system was developed to measure the ion temperature and flow velocity of field-reversed configuration (FRC) plasmas in the FRC amplification via a translation-collisional merging (FAT-CM) device. Adopting a Czerny-Turner mount monochromator and 16-channel photomultiplier tube array, the developed IDS system achieves high wavelength resolution and fast time response. In addition, two vertically aligned optical paths share the optical system up to the monochromator and then branch just before the detector, successfully reducing crosstalk to <1%. The Doppler broadening was measured at two measurement points in the FAT-CM device, simultaneously, and ion temperatures of ∼50eV were measured. Toroidal spin-up from 7 to 15 km/s and a steady flow velocity of ∼10 km/s were estimated from the Doppler shift obtained by the developed system. The observation of the toroidal flow velocity and the spatial profile of the ion temperature of the FRC plasma in the FAT-CM device were realized. These spectroscopic diagnostic's double chord capabilities will aid in understanding and improving the FRC plasmas.

Molecular dynamics analysis of water flow through a multiply connected carbon nanotube channel

The filling process of nanoconduits is an active research topic. In this study, we use molecular dynamics simulations to identify the filling process of water molecules in a multiply connected carbon nanotube (MCCNT). For water permeation, a local change in the channel cross-section affects the water filling of MCCNTs because it may lead to irregularities in the permeation profile. A decrease in hydrogen bonds at the junctions of the structure characterizes the permeability of MCCNTs. In contrast to pristine CNTs, the complex nanochannel exhibits a different imbibition profile due to the energy changes at the junction. Next, we examine the local water density and velocity patterns in MCCNT channels to understand how junction regions affect steady-state water transport. We find that there is congestion and irregularities in steady water flow density and velocity profiles. Through this study, we expect to develop effective channels with more complex geometries for water purification and drug delivery.

Influence of fracture connectivity and shape on water seepage of low-rank coal based on CT 3D reconstruction

The shape and connectivity characteristics of coal fractures are important factors that affect the permeability of coal and the migration of water in the coal during water injection. In this study, a microscopic and mesoscopic fracture model of coal is constructed by using CT 3D reconstruction technology. Based on this model, the fracture connectivity parameters are selected and analyzed, and the gray correlation method for comprehensive evaluation is adopted to determine the relationship between permeability and fracture connectivity. Then, the shape factor η is introduced, the water injection seepage flow is simulated through the Navier-Stokes equation, and the seepage in the fractures with different shape factors is analyzed. The results show that the permeability of coal have a strong correlation with the fracture connectivity parameters, and the correlation order is average coordination number > porosity > maximum Feret diameter. Furthermore, the fracture shape factor is positively correlated with the maximum Feret diameter. In addition, the steady flow velocity increases with the increase of the shape factor. The fractures with η > 2 significantly increases the permeability of coal, but fractures with large shape factors are still the most important channels for seepage.

A phenomenological description of the transient single-phase pore velocity period using the resistance force-velocity relationship

A new approach to determine the transient period towards steady state pore flow velocity for fluids propagating through porous media under constant pressure condition is presented. The transient expression relates to the mean pore velocity rather than the fluid pressure conventional considered when characterizing transient behavior in porous media. It is based on the general, resistance force-velocity relationship, and is therefore analogous to the approach used when calculating transient periods for objects falling through resisting air and for the increase in electric currents towards respective steady state values. The transient is caused by inertia forces and characterized by a relaxation time comprising fluid density and viscosity together with porous medium properties as porosity and absolute permeability. Results show that the transient period increases with decreasing medium porosity and fluid viscosity and with increasing fluid density and absolute permeability of the medium. The transient period is negligibly small for typical fluid/medium property values characterizing typical subterrain sandstone reservoirs. Significant transient periods, occasionally observed during laboratory fluid injection tests, are therefore caused by other time-dependent processes not captured by the transient expression presented herein, e.g., fines migration or electrokinetic phenomena. Cited as: Standnes, D. C. A phenomenological description of the transient single-phase pore velocity period using the resistance force-velocity relationship. Advances in Geo-Energy Research, 2022, 6(2): 104-110. https://doi.org/10.46690/ager.2022.02.03

On the determination of the absolute velocity of steady flows of a baroclinic fluid with applications to ocean currents

The problem of determining the absolute velocity of marine currents, including its barotropic component, is revisited. A generalization of the classical Needler’s formula is discussed for a Boussinesq fluid and it is shown that the steady flow solution can be deduced from a variational principle that uses the constants of motion existing in the problem. A simple model of a steady flow is considered when the Bernoulli function consists of two terms. The first term is proportional to the square of Ertel’s potential vorticity and the second term is a quadratic function of the fluid buoyancy. This model is applied to mimic the circulation in the western Mediterranean Sea near the African coast. Alternatively, “potential temperature – salinity” coordinates are applied to construct the stream-tubes and infer the steady flow velocity in the simplest case of the Bernoulli function being proportional to the product of the above two variables.

Optimal Homotopy Asymptotic Method for Investigation of Effects of Thermal Radiation, Internal Heat Generation, and Buoyancy on Velocity and Heat Transfer in the Blasius Flow

In this study, analytical examination of effects of internal heat generation, thermal radiation, and buoyancy force on flow and heat transfer in the Blasius flow over flat plate has been presented. The governing nonlinear partial differential equations of the problem are transformed into a set of coupled nonlinear third-order ordinary differential equations by the similarity variable method and have been systematically solved using the optimal homotopy asymptotic method. The main aim of the present study is to inspect the effects of various physical parameters in the flow model on velocity and heat transfer in steady two-dimensional laminar boundary layer flow with convective boundary conditions. The influences of the Grashof number, internal heat generation, the Biot number, radiation parameter, and the Prandtl number on the skin-friction coefficient, the fluid velocity profile, and temperature distribution have been determined and discussed in detail through several plots. The finding revealed that the fluid velocity and temperature delivery upsurge with snowballing in the values of the Biot number and internal heat generation parameters. The temperature profile of the fluid declines contrary to the value of the Grashof number and the Prandtl number but increases with thermal radiation. Moreover, it is found that the skin-friction coefficient and the rate of heat intensify with the Grashof number, internal heat generation, the Biot number, and thermal radiation parameter. The obtained result is likened with the previously published numerical results in a limited case of the problem and shows an excellent agreement.

Enhanced mass transfer in air oscillating in a channel with periodically varying radius

The effect of high frequency oscillations of air column in a channel of variable radius on vapor diffusion is experimentally studied. It is found that significant enhancement of longitudinal mass transfer takes place due to steady vortical flows excited in channel cells. In parallel with experiments in air we conducted PIV experiments with low viscous fluids in order to study the steady flow structure in the same range of dimensionless frequency as in diffusion experiments with air. It is revealed that additional mass transfer Ds associated with the steady flow is a function of steady flow dimensionless velocity V, which depends on frequency ω and pulsating Reynolds number. It is followed from PIV measurements that Ds ∼ V2 and in the studied range of oscillation frequency ω, the additional diffusion rate Ds is an order larger than the molecular diffusion D. Comparison of our experimental data with data of other authors obtained in the experiments with channels of another geometry shows that increase of variation of a channel radius results in significant enhancement of steady flow velocity and, therefore, mass transfer.

Relating the Flow Processes and Bedforms of Steady-State and Waning Density Currents

© Copyright© 2020 de Cala, Ohata, Dorrell, Naruse, Patacci, Amy, Simmons, McLelland and McCaffrey. The interaction between turbidity currents and mobile substrates can lead to the development of different types of bedforms. Although much research has been conducted on bedform development beneath open channel flows, research into bedform development beneath waning gravity currents is relatively rare. Analysis of density current-related bedform development has therefore relied upon open channel flow phase diagrams. We report on an experimental study designed to assess the development of bedforms under steady and waning saline density currents. The experimental density currents developed stepped density profiles in which a higher-density basal zone was separated from the ambient fluid by a zone of intermediate density; any bedforms that developed were contained within the bottom layer of the current. Under different conditions ripples, dunes, downstream migrating antidunes and long wavelength antidunes were observed to form and could be distinguished based on their interactions and phase relationships with the upper surface of the lower denser layer of the current. Due to limited mixing between the upper and lower layer of the current and maintenance of current momentum, currents set with slowing discharge flow rates maintained a steady flow velocity in the lower layer of the flow. As a result, sustained bedform formative conditions were achieved within this lower layer, while waning current conditions effected the rest of the flow. Under waning currents, it was seen how pre-existing bed states can determine the subsequent evolution of bedforms. This illustrates the limitations of existing phase diagrams as they do not account for trajectory or rate of passage of flows through different bedform phase spaces. In order to establish a reliable quantitative association between the flow regime and the type of bedform development, it is critical to adopt an appropriate Froude number calculation method for stratified flow. The updated density current phase diagram indicates supercritical flow can be achieved at lower flow velocities than for open channel flows due to the effects of reduced gravity. Bedform depositional structures found in outcrop and on the modern sea floor provide data that helps to interpret the hydrodynamic and sedimentological character of the current that formed them. Therefore, understanding the processes involved in bedform development beneath density currents will enable more accurate estimation of the properties of flows.

Numerical and analytical predictions of nuclear steam generator secondary side flow field during blowdown due to a feedwater line break

For the structural integrity evaluation of pressurized water reactor (PWR) steam generator (SG) tubes subjected to transient hydraulic loading, determination of the tube-to-tube gap velocity and static pressure distributions along the tubes is prerequisite. This paper addresses both computational fluid dynamics (CFD) and analytical approaches for predicting the tube-to-tube gap velocity and static pressure distributions during blowdown following a feedwater line break (FWLB) accident at a PWR SG. First of all, a comparative study on CFD calculations of the transient velocity and pressure distributions in the SG secondary sides for two different models having 30 or no tubes is performed. The result shows that the velocities of sub-cooled water flowing between any adjacent two tubes of a tubed SG model during blowdown can be roughly estimated by applying the specified SG secondary side porosity to those of the no-tubed SG model. Secondly, simplified analytical approximate solutions for the steady two-dimensional SG secondary flow velocity and pressure distributions under a given discharge flowrate are derived using a line sink model. The simplified analytical solutions are validated by comparing them to the CFD calculations.

Vortex dynamics and scalar transport in the wake of a flat-plate controlled by a vibrating trailing-edge flap

We investigate the onset and development of vortical flow disturbances introduced into the wake of a horizontally fixed flat-plate by means of the controlled motion of a trailing edge flap. The vibrating mechanics of the flap allows for the introduction of both impulsive and harmonic weak amplitude velocity disturbances which are propagated downstream into the wake flow of the flat-plate. Quantitative experimental and numerical predictions of both steady and unsteady wake flow velocity resulting from different flapping frequencies are made at low Reynolds numbers (Re < 104). Frequency response tests of the wake confirmed the existence of two dominant frequencies where the wake flow organises with a particular arrangement of downstream moving vortex structures. Numerical predictions of steady (unforced) and forced wake velocity profiles and kinetic energy profiles are in good agreement with the experimental results. In order to understand practical implications of the dominant vortex structures in scalar transport, we have extended the numerical part of the study solving for the concentration equation of a passive scalar being injected in particular regions of the physical domain. A spatial correlation between the trajectory of vortex structures and the scalar concentration downstream the wake is observed. Moreover, the onset of tip vortex structures produced during the forcing cycle seems to be responsible of a local increase of scalar concentration near the span wise flap ends.

Nonlinear dynamics of functionally graded pipes conveying hot fluid

For improved stability of fluid-conveying pipes operating under the thermal environment, functionally graded materials (FGMs) are recommended in a few recent studies. Besides this advantage, the nonlinear dynamics of fluid-conveying FG pipes is an important concern for their engineering applications. The present study is carried out in this direction, where the nonlinear dynamics of a vertical FG pipe conveying hot fluid is studied thoroughly. The FG pipe is considered with pinned ends while the internal hot fluid flows with the steady or pulsatile flow velocity. Based on the Euler–Bernoulli beam theory and the plug-flow model, the nonlinear governing equation of motion of the fluid-conveying FG pipe is derived in the form of the nonlinear integro-partial-differential equation that is subsequently reduced as the nonlinear temporal differential equation using Galerkin method. The solutions in the time or frequency domain are obtained by implementing the adaptive Runge–Kutta method or harmonic balance method. First, the divergence characteristics of the FG pipe are investigated and it is found that buckling of the FG pipe arises mainly because of temperature of the internal fluid. Next, the dynamic characteristics of the FG pipe corresponding to its pre- and post-buckled equilibrium states are studied. In the pre-buckled equilibrium state, higher-order parametric resonances are observed in addition to the principal primary and secondary parametric resonances, and thus the usual shape of the parametric instability region deviates. However, in the post-buckled equilibrium state of the FG pipe, its chaotic oscillations may arise through the intermittent transition route, cyclic-fold bifurcation, period-doubling bifurcation and subcritical bifurcation. The overall study reveals complex dynamics of the FG pipe with respect to some system parameters like temperature of fluid, material properties of FGM and fluid flow velocity.

Slow steady flow of a skyrmion lattice in a confined geometry probed by narrow-band resistance noise

Using resistance fluctuation spectroscopy, we observe current-induced narrow-band noise (NBN) in the magnetic skyrmion-lattice phase of micrometer-sized MnSi. The NBN appears only when electric-current density exceeds a threshold value, indicating that the current-driven motion of the skyrmion lattice triggers the NBN. The observed NBN frequency is 10-10$^4$ Hz at $\sim$10$^{9}$ A/m$^{2}$, implying a skyrmion steady flow velocity of 1-100 $\mu$m/s, 3-5 orders of magnitude slower than previously reported. The temperature evolution of the NBN frequency suggests that the steady flow entails thermally activated processes, which are most likely due to skyrmion creation and annihilation at the sample edges. This scenario is qualitatively supported by our numerical simulations considering boundary effects, which reveals that the edges limit the steady flow of skyrmions, especially at low temperatures. We discuss a mechanism that dramatically slows the skyrmion steady flow in a microfabricated specimen.

On the measurement of ram-pump power by changing in water hammer pressure wave energy

Abstract The renewable energy protocol in the world pushed most countries to extensive use of renewable energy sources, in exchange for a reduction of energy from conventional sources. In this article, the possibilities of exchange the water hammer energy to a column of water pressure evaluated experimentally. For this purpose, a ram pump made by two-inch internal diameter. Results indicated that ram pump power such as relative useful power (Pd/PT) and relative waste power (Pw/PT) were depended to length to diameter ratio of drive pipe (L/D), the relative energy due to steady flow velocity and impulse valve features (Ea/Ei), and the ratio of required pumping energy to maximum energy of water hammer (Ep/Em). The results showed that the mountainous area has potential to generate energy from water hammer as renewable energy, for a water system in highland that continuously needs to pumping water.

Micro-dynamics of neutral flow induced dusty plasma flow

We present a detailed experimental study of gas flow induced motion of dust particles in a DC glow discharge plasma. The characteristics of the dust dynamics are investigated as a function of the differential gas flow rate, the background neutral pressure, the dust particle size, and the neutral species of the gas. The experiments have been carried out in the table top Dusty Plasma Experimental (DPEx) device in which a plasma is created between a disk shaped anode and a grounded cathode in a Π-shaped Pyrex glass tube. The asymptotic steady state flow velocity of the injected micron sized dust particles is found to increase with an increase in neutral flow velocity and decrease with an increase in the background pressure. Furthermore, this velocity is seen to be independent of the size of the dust particles, but decreases with an increase in the mass of the background gas. A simple theoretical model, based on estimates of the various forces acting on the dust particles, is used to elucidate the role of neutrals in the flow dynamics of the dust particles. Our experiments thus provide a detailed microscopic understanding of some of the past phenomenological observations of dust flows in the DPEx device and can prove useful in future experimental implementations of dust flow experiments.

Similarity and vortex-acoustic lock-on behavior in thermoacoustic oscillation involving vortex shedding

In engineering, the combustion chamber with a backward step is very popular, and it is a kind of flame stabilizer. In this type of combustion chamber, there will be shedding vortices at the step due to the instability of the flow field. The shedding vortices will carry reactants to move downstream and burn, resulting in unstable heat release and then pressure and velocity fluctuations of the sound field, thereby, finally, forming a combustion-vortex-acoustic interaction process. If a positive feedback loop is formed between the unstable heat release and the pressure fluctuation of sound field, combustion instability will occur, and it is also referred to as thermoacoustic oscillation due to vortex shedding. Combustion instability frequently occurs in many practical systems or equipment, and its induced significant pressure oscillations have a serious influence on the normal operation of the equipment. Recently, the combustion instability has been extensively studied experimentally, but the theoretical investigation on its nature is still rare. Since combustion instability is a complicated nonlinear phenomenon, it is necessary to study its nature from the viewpoint of nonlinear dynamics. Based on the one-dimensional simplified model of thermoacoustic instability involving vortex shedding proposed by Matveev and Culick, the typical nonlinear phenomenon in thermoacoustic oscillation induced by vortex shedding is studied. The study focuses on the initial value sensitivity of the system, the influence of key parameters on thermoacoustic oscillation, and the phenomenon of vortex-acoustic lock-on. Firstly, the Galerkin method is used to approximate the governing equation, and the partial differential equations are reduced to a set of ordinary differential equations. Then, the first ten modes are selected, and the pressure and velocity fluctuations of sound field under different system parameters are obtained by MATLAB program. Finally, the thermoacoustic instability of the system under different initial disturbances, the influences of different steady flow velocity on the thermoacoustic oscillation of the system, and the phenomenon of vortex-acoustic lock-on in thermoacoustic oscillation are studied in detail. The results show that the system of thermoacoustic oscillation involving vortex shedding is extremely sensitive to initial values, and there are a rich variety of nonlinear phenomena. With steady flow velocity increasing, the amplitude of pressure fluctuation augments generally. However, the similar structures are found in several intervals of steady flow velocity, and the amplitude first decreases and then increases. In particular, it is verified that the system oscillates periodically by integer (fp/fs) multiple of the vortex impinging frequency (fs), that is, the vortex-acoustic frequency locking with the number of revolutions fp/fs, which is found in experiment and can be regarded as an important characteristic of periodic thermoacoustic oscillation.

Depletion-model-based numerical simulation of the kinetics of red blood cell aggregation under sinusoidal pulsatile flow.

Previous numerical modeling studies on red blood cell (RBC) aggregation have elucidated the inverse relationship between shear rate and RBC aggregation under steady flow. However, information on the cyclic variation in RBC aggregation under pulsatile flow remains lacking. RBC aggregation was simulated to investigate the complex interrelationships among the parameters of RBC motion under pulsatile flow. A two-dimensional particle model was used to simulate RBC motion driven by hydrodynamic, aggregation, and elastic forces in a sinusoidal pulsatile flow field. The kinetics of RBCs motion was simulated on the basis of the depletion model. The simulation results corresponded with previously obtained experimental results for the formation and destruction of RBC aggregates with a parabolic radial distribution during a pulsatile cycle. In addition, the results demonstrated that the cyclic variation in the mean aggregate size of RBCs increased as velocity amplitude increased from 1 cm/s to 3 cm/s under a mean steady flow of 2 cm/s, as mean steady flow velocity decreased from 6 cm/s to 2 cm/s under a velocity amplitude of 1.5 cm/s, and as stroke rate decreased from 180 beats per minute (bpm) to 60 bpm. The present simulation results verified previous experimental results and improved the current understanding of the complex spatiotemporal changes experienced by RBC aggregates during a sinusoidal pulsatile cycle.