Ejection Of Fluid Research Articles

Direct numerical simulation of turbulent particle-laden flows: effects of Prandtl and Stokes numbers

The effect of molecular Prandtl number on the turbulent heat transfer of a non-isothermal turbulent channel flow laden with particles with four different Stokes number is investigated using direct numerical simulation coupled with a Lagrangian particle tracking. The flow configuration is a downward vertical channel with side walls kept at constant temperature. A total of 16 test cases with four different Prandtl numbers of Pr = 0.71, 1, 3, 7, and four particle sizes with the Stokes numbers of St= 40, 60, 100, 190 are considered. The mass loading, particle-to-fluid density ratio, and specific heat ratio are constant for all cases and they are equal to 0.57, 7298, and 0.39, respectively. It is shown that by the addition of particles, the heat transfer rate decreases and the thickness of the conductive sublayer thickness increases for all cases. The percentage of heat transfer modulation resulting from the addition of particles is almost independent of the Prandtl number but it slightly depends on the size of the particles, with the maximum being for smaller particles. The mean and rms values of temperature, temperature-velocity correlations, mean energy equation, and temperature variance budgets are presented. Contours of temperature in planes parallel to the wall and normal to the streamwise direction are also reported. At higher Prandtl numbers, the temperature contours clearly visualize the mushroom shaped structures formed as a result of the ejection of low-speed fluid from the wall.

Numerical Analysis of Heat Transfer of Eyring Powell Fluid Using Double Stratification of Magneto-Hydrodynamic Boundary Layer Flow

Heat transfer fluids play a vital role in many engineering and industrial sectors such as power generation, chemical production, air-conditioning, transportation and microelectronics.
 Aim: To numerically investigate the effect of double stratification on magneto-hydrodynamic boundary layer flow and heat transfer of an Eyring-Powell fluid.
 Study Design: Eyring-Powell fluid is one of the non-Newtonian fluid that possess different characteristics thus different mathematical models have been formulated to describe such fluids by appropriate substitution into Navier-Stoke’s equations. The challenging complexity and the nature of the resultant equations are of great interest hence attract many investigations.
 Place and Duration of Study: Department of Mathematics and Actuarial Science, Kenyatta University, Nairobi, Kenya between December 2019 and October 2020.
 Methodology: The resultant nonlinear equations are transformed to linear differential equations by introducing appropriate similarity transformations. The resulting equations are solved numerically by simulating the predictor-corrector (P-C) method in matlab ode113. The results are graphically depicted and analysed to illustrate the effects of magnetic field, thermophoresis, thermal stratification, solutal stratification, material fluid parameters and Grashoff number on the fluid velocity, temperature, concentration, local Sherwood number and local Nusselt number.
 Results: The results show that increasing the magnetic field strength, thermophoresis, thermal stratification and solutal stratification lead to a decrease in the fluid velocity, temperature, Sherwood number, Nusselt number and skin friction while an increase in the magnetic field strength, thermal stratification, solutal stratification, and thermophoresis increases the fluid concentration.
 Conclusion: The parameters in this study can be varied to enhance heat ejection of Eyring-Powell fluid and applied in industries as a coolant or heat transfer fluid.

Quantitative High-speed Assessment of Droplet and Aerosol From an Eye After Impact With an Air-puff Amid COVID-19 Scenario

To quantify aerosol and droplets generated during noncontact tonometry (NCT) and assess the spread distance of the same. This was an experimental study on healthy human volunteers (n=8 eyes). In an experimental setup, NCT was performed on eyes (n=8) of human volunteers under normal settings, with a single and 2 drops of lubricant. High-speed shadowgraphy, frontal lighting technique, and fluorescein analysis were used to detect the possible generation of any droplets and aerosols. Mathematical computation of the spread of the droplets was then performed. In a natural setting, there was no droplet or aerosol production. Minimal splatter along with droplet ejection was observed when 1 drop of lubricant was used before NCT. When 2 drops of lubricant were instilled, a significant amount of fluid ejection in the form of a sheet that broke up into multiple droplets was observed. Some of these droplets traversed back to the tonometer. Droplets ranging from 100 to 500 µm in diameter were measured. There was no droplet generation during NCT performed in a natural setting. However, NCT should be avoided in conditions with high-tear volume (natural or artificial) as it would lead to droplet spread and tactile contamination.

Thermography analysis and porosity formation during laser beam welding of AA5083-H111 aluminum alloy

In this work, the thermal characteristics of the weld pool during Yb:YAG laser welding of the AA5083-H111 aluminum alloy were captured using an infrared thermal imaging camera and a numerical model was developed to predict the temperature fields using COMSOL Multiphysics software. On comparing the measured and predicted temperature of the weld pool surface, the deviation was below 10 °C and the average experimental error was not more than 1%. It shows the reliability of IR camera used in this investigation. Also, it was apparent from the thermal images that at a higher beam power, an erratic molten pool was created due to the instability of keyhole and spatters were ejected from the molten pool. The higher recoil pressure built at the walls of keyhole due to the high intensity of the laser beam and instigation of the ejected fluid flow mechanism was responsible for this occurrence. Also, the formation and floating mechanisms of process-induced porosities were analyzed. Porosities were identified in the weldments processed with longer shielding gas blown distance (30 mm), whereas other welds had no porosities. Since the gas blown distance was more, gas pressure over the molten pool was not sufficient to suppress the plasma plume and, thereby, results in porosity formation. Interestingly, a high number of porosities were evident at the toe of the weld bead and it was assumed to be caused by the high thermal gradient-induced Marangoni flow. This study provides a better understanding of molten pool behavior, porosity formation and its floating mechanism.

Vortex self-similarity in an impinging synthetic jet and its three-stage evolution

The periodic ejection of fluid from a cavity or channel generates a train of counter-rotating vortex pairs that synthesizes a coherent fluctuating flow, known as a Synthetic Jet. In recent years, such flows found applications in the electronics cooling industry by impinging the flow onto heated surfaces, and in aerodynamics for boundary layer control. This paper intends to simplify the fluid dynamics of Synthetic Jets using the Lamb-Oseen solution to deepen the fundamental understanding of these flows. We used experimentally validated Direct Numerical Simulations to compare those data with the analytical approach. The numerical experiments were carried using the Finite Volume Method through the commercial software ANSYS Fluent. The analytical approach showed excellent agreement with the DNS data, except early in the jet cycle due to channel effects, and late in the cycle because of merging and viscous dissipation of vorticity. Appropriate non-dimensionalization of the data demonstrated that the vortices are self-similar and depend on the vortex-distance-to-radius ratio, regardless of time or the case studied. The evolution of the vortex radius evidenced the existence of three stages: (1) Actuation as the vortices emerge from the channel, (2) separation from the channel and free-flight toward the wall, and (3) convection as a remnant stationary vortex induces extra translational velocity on the primary vortex.

Longitudinal muscular column in the prostatic urethral wall: Its form, shape, and possible function based on mathematical simulation in ejaculation.

The shape and function of the longitudinal muscular column (LMC) of the prostate have not been established in detail. The present study was undertaken to elucidate the roles of the LMC of the posterior wall of the prostatic urethra (PSU) in the emission phase of ejaculation by investigating the form and muscular arrangement of the LMC. Prostates and urinary bladders were obtained from 14 Korean adult cadavers. Nine specimens were histologically analyzed using hematoxylin and eosin, Masson's trichrome, and Verhoeff-van Gieson staining. Two specimens were scanned using microcomputed tomography (micro-CT), and all scanned images were reconstructed into a three-dimensional model. At the proximal level of the prostate, the ejaculatory ducts (EDs) and prostatic utricle (PU) together were surrounded by circular smooth-muscle fibers. However, at the seminal colliculus (SC) where the EDs and PU opened, they were mainly surrounded by an abundance of longitudinal fibers. The longitudinal fibers posterior to the EDs and PU formed a distinctive LMC in the posterior urethral wall. In histologic sections and micro-CT images, the LMC extended distally from the level of the SC to the level of the membranous urethra (MBU). We simulated a potential mechanism of LMC using a mathematical model of its movements. Comprehensive analyses based on in-depth assessment of histologic characteristics and micro-CT images demonstrated extension of the LMC from the level of the SC to the level of the MBU, enabling a better understanding of ejaculation physiology involving the LMC. These results suggest that the LMC in the posterior wall of the PSU is a critical component of ejaculation by facilitating the ejection of seminal vesicle fluid into the PSU via well-coordinated contractions.

Исследование процесса эжектирования бурового раствора сквозь межлопастное пространство калибратора-эжектора

Исследование процесса эжектирования бурового раствора сквозь межлопастное пространство калибратора-эжектора

An experimental study of a multi-orifice synthetic jet with application to cooling of compact devices

In the present work, the flow characteristics of free and impinging synthetic jets formed from a single cavity but with a different number of orifices are investigated using the particle image velocimetry technique. A synthetic jet is a zero-net mass-flux device that formed by periodic ejection and suction of fluid through a small opening. The flow characteristics are used to explain the heat transfer results in the literature. The number of satellite orifices, distance between orifices, and location of the surface from orifices are varied to observe the phenomenon of jet interaction and its influence on flow recirculation. The results show that interaction between adjacent jets causes the diversified flow characteristics of the multiorifice jet with respect to a single orifice jet. The multiorifice jet exhibits significantly higher entrainment and mixing compared to its equivalent diameter of a single orifice jet. Moreover, results from the impinging jet corroborate that the impingement of vortex pairs, their breakdown, and formation of a strong wall jet are responsible for a high heat transfer coefficient for the case of larger surface spacing (z/d ≥ 8; normalized distance between orifice and surface). However, for impingement at small surface spacing (z/d ≤ 2), change in recirculation behavior with different orifice configurations can lead to a variation in the heat transfer coefficient. For the large and medium surface spacing (2 < z/d < 8), the center orifice gets sufficient time to develop, which draws the satellite and impingement jets as a single orifice jet. In the case of large surface spacing, the wall jet vortices are not attracted during the suction stroke. While for medium surface spacing, wall jet vortices are closer to the orifice and easily entrained during the suction stroke and form a recirculating region. In the case of small surface spacing, the center jet does not get sufficient time, and hence both center and satellite jets impinge separately. It was found that the center jet having higher ejection velocity impinges earlier than the satellite jet and the wall jet vortex formed from the center orifice drives along a wall jet. Therefore, recirculation is absent for smaller surface spacing, and fresh fluid is sucked and impinges on the surface in each cycle. This study expands the current knowledge of multiorifice free and impinging jets and establishes a relationship between heat transfer and fluid flow, which eventually facilitates an efficient and effective heat transfer system for compact devices.

Assessment of causes of overpressure different from sub-compaction: Application in unconventional reservoir

The necessity for hydrocarbon-producing countries to increase their reserves has led to companies exploring the deposits available in source rocks that might be over-pressured and thus, strict rules are required for their development. Overpressure, which may result in wellbore stability problems, could result from several causes such as mechanical effects, dynamic transfer, chemical stress, thermal stress, among others, in which undercompaction is frequently the main cause, generated when the sediment deposition velocity exceeds the fluid ejection rate.The expansion of fluids generated by thermal stresses and the reduction of porosity caused by chemical stresses may be among the other causes of overpressure in shales.
 The new methodology presented in this paper makes it possible to determine the pressure due to thermal stresses caused by the cracking of kerogen and oil in shales. In addition, petrophysical and geochemical models are considered in order to precisely ascertain the increase in pore pressure due to temperature andfluid expansion. An increase of 20% in pressure is seen when compared with undercompaction. As a result of this methodology, the mud window was optimized and the hydrocarbons, generated under subsurface the conditions (pressure, temperature) analyzed, were quantified.

The structure of a turbulent line fountain

Line fountains form when heavy miscible fluid is ejected steadily upwards as a jet from a high-aspect-ratio rectangular slot, of length $L$ and half-width $b_{0}$, into lighter quiescent surroundings. Viewed along the slot from one end, previous observations reveal that the ejected fluid mixes with the environment and reaches a peak height before partially collapsing back downward under gravity to form a fountain whose top thereafter fluctuates vertically about a mean height. While the motion as perceived from this single view has provided insights that have successfully guided theoretical predictions for the initial rise height, until now a wider understanding of line fountains, and corresponding predictive capability, has been limited to this single prediction due to a lack of any other observational data. Indeed, the general behaviour of line fountains, including the structure internally and along the spanwise length $L$ of the slot, has not been reported previously. To address this, flow visualisations and comprehensive measurements of saline fountains in an aqueous environment are presented here that reveal their complex overall structure and behaviours. After establishing the uniformity of the source conditions from slots of aspect ratio $600:1$ and $300:1$, we first show that double-averaged (spanwise and time) rise heights $\overline{\overline{z}}_{v}/b_{0}$ scale on $Fr_{0}^{4/3}$, $Fr_{0}$ being the source Froude number, with vertical fluctuations being circa 20 % of these heights. Then, simultaneously interrogating the flow as viewed from above and from the side onto the spanwise dimension, we identify three distinct patterns of behaviour. Instrumental to distinguishing these behaviours were the contrasting signatures we observed in the time series of rise height departures from the mean which led us to the following classification: (i) non-uniform flapping for $0.05\lesssim \overline{\overline{z}}_{v}/L\lesssim 0.30$, in which the lateral motion of the fountain takes the form of an oscillatory wave with a wavelength of $2L/3$ (approx.); (ii) uniform flapping for $0.30\lesssim \overline{\overline{z}}_{v}/L\lesssim 0.45$, in which the entire fountain sways to the left and then to the right side of the slot; and (iii) disorganised flapping for $\overline{\overline{z}}_{v}/L\gtrsim 0.45$. Regarding the internal structure, we show that unlike a classic round fountain, eddying structures comparable in scale with the rise height form towards the top of the fountain, and the counterflow forms predominantly to one side of the jet. We then identify the single dominant mechanism driving the flapping motions, successfully linking the wave-like behaviour observed along the span to the internal structure and vertical oscillations. Quantifying the oscillatory motions, both the vertical and flapping frequencies scale as $Fr_{0}^{-2}$, and we demonstrate and explain a robust coupling between these frequencies that follows a ratio of 2:1.

Pseudophase change effects in turbulent channel flow under transcritical temperature conditions

We have performed direct numerical simulations of compressible turbulent channel flow using R-134a as a working fluid in transcritical temperature ranges ($\unicode[STIX]{x0394}T=5$, 10 and 20 K, where $\unicode[STIX]{x0394}T$ is top-to-bottom temperature difference) at supercritical pressure. At these conditions, a pseudophase change occurs at various wall-normal locations within the turbulent channel from $y_{pb}/h=-0.23$ ($\unicode[STIX]{x0394}T=5$ K) to 0.89 ($\unicode[STIX]{x0394}T=20$ K), where $h$ is the channel half-height and $y=0$ the centreplane position. Increase in $\unicode[STIX]{x0394}T$ also results in increasing wall-normal gradients in the semi-local friction Reynolds number. Classical, compressible scaling laws of the mean velocity profile are unable to fully collapse real fluid effects in this flow. The proximity to the pseudotransitioning layer inhibits turbulent velocity fluctuations, while locally enhancing the temperature and density fluctuation intensities. Probability distribution analysis reveals that the sheet of fluid undergoing pseudophase change is characterized by a dramatic reduction in the kurtosis of density fluctuations, hence becoming thinner as $\unicode[STIX]{x0394}T$ is increased. Instantaneous visualizations show dense fluid ejections from the pseudoliquid viscous sublayer, some reaching the channel core, causing positive values of density skewness in the respective buffer layer region (vice versa for the top wall) and an impoverishment of the turbulent flow structure population near pseudotransitioning conditions.

PIV-based characterization of puffs in transitional pipe flow

High frame rate stereo-PIV was conducted on circular cross sections of pipe flow to examine velocity variations inside turbulent puffs. A registration method was developed to recognize strong ejections of fluid from the wall near a puff’s trailing edge, and the method was employed to determine ensemble averages of multiple puff occurrences. Both individual puff reconstructions and the ensemble average revealed that these ejections were accompanied consistently by a hairpin vortex that was, in turn, frequently part of a streamwise-aligned hairpin sequence. This sequence is associated with a region that starts near the wall one diameter upstream of the puff’s trailing edge and spreads to the center of the pipe at the trailing edge before shrinking back towards the wall over the next three diameters downstream. The sequence is accompanied by additional hairpins and disturbances that extend over the pipe cross section already by the trailing-edge location. The puff data were used also to search for azimuthal modal patterns within streamwise velocity variations. These modal patterns were shown to be a robust feature of experimental puffs. Upstream patterns were typically disrupted by the trailing edge ejection and hairpin, resulting in downstream patterns of different mode and character. On average, modal patterns existed over longer distances than those identified previously in numerical simulations.

Influence of internal orifice geometry on synthetic jet performance

The periodic ingestion and ejection of fluid through an orifice yield vortex rings forming an unsteady jet. The ability to impart momentum with a zero net mass flux makes synthetic jet actuators coveted components in flow control applications. Previous studies underlined the influence of geometrical parameters on synthetic jet evolution. This investigation introduces the orifice lip ratio as a new geometric variation that can influence the performance of the jet. We assess the sensitivity of synthetic jet efficiency to this parameter. Comparisons of test configurations establish the lip ratio as a pivotal parameter and indicate noticeable differences in the exit velocity. The results also highlight the dependence of the jet formation criterion on the orifice lip ratio. The analysis conclusively demonstrates the significance of the orifice lip ratio in the design and optimisation of synthetic jet actuators.

Noninvasive Determination of Vortex Formation Time Using Transesophageal Echocardiography During Cardiac Surgery.

Trans-mitral blood flow produces a three-dimensional rotational body of fluid, known as a vortex ring, that enhances the efficiency of left ventricular (LV) filling compared with a continuous linear jet. Vortex ring development is most often quantified with vortex formation time (VFT), a dimensionless parameter based on fluid ejection from a rigid tube. Our group is interested in factors that affect LV filling efficiency during cardiac surgery. In this report, we describe how to use standard two-dimensional (2D) and Doppler transesophageal echocardiography (TEE) to noninvasively derive the variables needed to calculate VFT. We calculate atrial filling fraction (β) from velocity-time integrals of trans-mitral early LV filling and atrial systole blood flow velocity waveforms measured in the mid-esophageal four-chamber TEE view. Stroke volume (SV) is calculated as the product of the diameter of the LV outflow track measured in the mid-esophageal long axis TEE view and the velocity-time integral of blood flow through the outflow track determined in the deep transgastric view using pulse-wave Doppler. Finally, mitral valve diameter (D) is determined as the average of major and minor axis lengths measured in orthogonal mid-esophageal bicommissural and long axis imaging planes, respectively. VFT is then calculated as 4 × (1-β) × SV/(πD3). We have used this technique to analyze VFT in several groups of patients with differing cardiac abnormalities. We discuss our application of this technique and its potential limitations and also review our results to date. Noninvasive measurement of VFT using TEE is straightforward in anesthetized patients undergoing cardiac surgery. The technique may allow cardiac anesthesiologists and surgeons to assess the impact of pathological conditions and surgical interventions on LV filling efficiency in real time.

An evaluation of the dissimilarity in heat and momentum transport through quadrant analysis for an unstable atmospheric surface layer flow

To elucidate the role of each fluid motion in the transport of momentum and heat fluxes in an unstable atmospheric surface layer (ASL) flow from single point measurements on a micrometeorological tower, we develop a novel method based on quadrant analysis where the contour maps of the turbulent statistics (fluxes, temperature variances and triple order moments between vertical velocity and temperature) are plotted on the quadrant planes between streamwise (u)–vertical (w) velocities, and vertical velocity (w)–temperature (T). We find that the dissimilarities in the heat and momentum transport with atmospheric stability are closely linked to the non-Gaussian nature of the joint probability density function (JPDF) between w and T. To highlight the changes in the fluid motions which cause this dissimilarity, we plot the contour maps of the third order moments between w and T on the u − w quadrant plane, and also of the streamwise momentum flux conditioned on every quadrant of u − w plane onto the T − w plane, referred to as octant analysis. The results indicate that in a highly-convective ASL, the cold downdrafts interspersed with strong ejections of hot fluid, carry a significant amount of both down-gradient and counter-gradient momentum flux, thus making the momentum transport inefficient. However, in a near-neutral ASL, the heat and momentum both are carried by the ejection and sweep quadrants of u − w quadrant plane, which indicates the temperature fluctuations are highly correlated with the high-speed and low-speed streaks commonly found in pure shear flows in the laboratory experiments.

Binucleation of Accessory Gland Lobe Contributes to Effective Ejection of Seminal Fluid in Drosophila melanogaster.

The adult male accessory gland in insects is an internal reproductive organ analogous to the mammalian prostate, and secretes various components in the seminal fluid. Products of the accessory gland in the fruit fly Drosophila melanogaster are known to control reproductive behaviors in mated females, such as food uptake, oviposition rate, and rejection of re-mating with other males, all of which increase male reproductive capacity. Production of larger amounts of accessory gland products is thus thought to result in higher male reproductive success. The epithelium of the Drosophila accessory gland lobe is composed of a unique population of binucleate cells. We previously predicted, based on measurements of cell size in mono/binucleate mosaic accessory glands, that binucleation results in a higher plasticity in cell shape, enabling more effective ejection of seminal fluid. However, the actual effect of binucleation on ejection of seminal fluid or reproductive capacity remained unclear, as we were unable to generate an organ with uniformly mononucleate cells. In the present study, we generated organs in which most of the epithelial cells are mononucleate by manipulating aurora B or fizzy-related to block binucleation. Mononucleation resulted in a less elastic accessory gland lobe, which decreased ejection volume and the oviposition of mated females; these effects were particularly pronounced over the long term. These results suggest that binucleation in accessory gland epithelial cells contributes to higher plasticity in the volume of this organ, and enhances male reproductive success through enabling ejection of larger amounts of seminal fluid.

Molecular Dynamics Study on the Mechanism of Nanoscale Jet Instability Reaching Supercritical Conditions

This paper investigates the characteristics of a nitrogen jet (the thermodynamic conditions ranging from subcritical to supercritical) ejected into a supercritical nitrogen environment using the molecular dynamics (MD) simulation method. The thermodynamic properties of nitrogen obtained by molecular dynamics show good agreement with the Soave-Redlich-Kwong (SRK) equation of state (EOS). The agreement provides validation for this nitrogen molecular model. The molecular dynamics simulation of homogeneous nitrogen spray is carried out in different thermodynamic conditions from subcritical to supercritical, and a spatio-temporal evolution of the nitrogen spray is obtained. The interface of the nitrogen spray is determined at the point where the concentration of ejected fluid component reaches 50%, since the supercritical jet has no obvious vapor-liquid interface. A stability analysis of the transcritical jets shows that the disturbance growth rate of the shear layer coincides very well with the classical theoretical result at subcritical region. In the supercritical region, however, the growth rate obtained by molecular dynamics deviates from the theoretical result.

Numerical study of foulant-water separation using hydrocyclones enhanced by ejection device: Effect of ejection velocity

To solve the blockage and fouling issues of sewage heat exchangers in sewage source heat pump, a novel de-foulant hydrocyclone with ejection device was proposed and studied with FLUENT software. The pressure and velocity fields were coupled by the SIMPLEC algorithm, whereas the Reynolds Stress Model was used to predict the 3-D strong swirling turbulent flow due to its anisotropic nature. The Discrete Phase Model was employed to study the particle motion. Results showed that, compared with the variable underflow-pipe diameter, adjusting the ejection velocity could significantly enhance the separation performance by achieving the low split ratio without the risk of blocking the underflow pipe. Unlike the effects of conventional ejectors, the increasing ejection velocity increased the back pressure of the underflow and hence decreased the split ratio. Specifically, if the ejection velocity was higher than a certain value (e.g., 2.0 m/s in this paper), all the 3-D strong swirling turbulent flows in hydrocyclones would be flushed out through the vortex finder by the ejected fluid. In addition, the range of the optimum ejection velocity did exist (e.g., 1.5–2.0 m/s in this paper). In general, the increasing ejection velocity increased the pressure and velocity in hydrocyclones.

Transitions between smooth and rough surfaces in turbulent channel flows for d- and k-type rough elements

This paper presents an experimental study on the transition from smooth to rough walls, and back to the smooth one, in turbulent closed-conduit flows. These transitions cause a shift on flow velocity profiles that changes their parameters when compared to the flow over a smooth wall. Different water flow rates were imposed in a closed conduit of rectangular cross section, where rough elements consisting of cavities of d- and k-type were positioned covering a part of the bottom wall of the test section. Reynolds numbers based on the channel half-height were moderate, varying between 7800 and 9600, and the regime upstream of the rough elements was hydraulically smooth. Experimental data for this specific case remain scarce and the involved physics rests to be understood. The flow field was measured by low frequency PIV (particle image velocimetry) and by flow visualization, the latter using a continuous 0.1 W laser, a high-speed camera, and scripts written by the authors. From the instantaneous fields measured with PIV, the mean velocities, fluctuations, shear stresses and turbulence production were computed. The results show the presence of oscillations in Reynolds stress and turbulence production, that are higher for the k-type roughness and were not shown in previous experimental works. From the high-speed movies, the angular velocities and frequencies of vortices in the cavities were computed, and the occurrence of fluid ejection from the cavities to upper layers of the flow was observed. A relation between the angular velocities of inner-cavities vortices and the oscillations in Reynolds stress and turbulence production is proposed.

Structural assessment of jet impingement loads under postulated main steam line break conditions

When a sudden rupture occurs in high energy lines, the ejection of inner fluid with high temperature and pressure causes jet impingement loads on adjacent components and structures, as well as on the ruptured pipe itself. This study examines the jet impingement phenomenon under postulated HELB (High Energy Line Break) conditions. In this context, typical numerical models were generated considering the SG (Steam Generator), MSL (Main Steam Line) piping, and containment. Subsequently, two sets of numerical analyses were carried out by changing the break locations. One set is computational fluid dynamics to assess the ejected fluid characteristics and define pressure histories. The other uses finite element analyses to calculate the stresses and displacements of the SG, piping, and containment building caused by the jet impingement loads. As a result, detailed analyses provided more realistic and conservative data than those in the ANSI/ANS 58.2 standard used in the current HELB design while the jet loads did not threat secondary structural integrity after the MSL piping break.