Flow Velocity Characteristics Research Articles

Effects of Fire Source Conditions on Vent Flow Velocity and Hot Gas Layer Characteristics in Two Rooms Connected by Vertical Opening

In this study, the effects of fire source conditions on the vent flow velocity and hot gas layer characteristics in two rooms (ROOM-I and ROOM-II) connected by a vertical opening (VO-I) were investigated experimentally. In ROOM-II, the vertical opening (VO-II) connected to the outside was installed. The fire sources were located at the centers of ROOM-I and ROOM-II, and the heat release rates were 1.32, 3.32, and 5.21 kW. Regarding the vent flow velocity, when the fire source was located in ROOM-I, the outflow of the hot gas and inflow of cold air occurred in the upper and lower parts of VO-I and VO-II, respectively, which were the same as those of VO-II when the fire source was located in ROOM-II. However, when the fire source was located in ROOM-II, the hot gas in the upper part of VO-I flowed out to ROOM-I and flowed again into ROOM-II. Additionally, the hot gas layer thickness and temperature rise in the fire and adjacent rooms were compared. In the fire room, the case where the fire source was placed in ROOM-I showed a thicker hot gas layer and a higher hot gas layer temperature rise than the case where the fire source was placed in ROOM-II. In the adjacent room, the case where the fire source was placed in ROOM-I showed a thinner hot gas layer and a higher hot gas layer temperature rise than the case where the fire source was placed in ROOM-II. The dependence of the hot gas layer temperature rise on the heat release rate was higher than that of the hot gas layer thickness.

Solute dispersion of Hershel-Bulkley fluid through an inclined artery

Different types of arteries in the human body possess inclinations that impact blood flow behavior and affect the effectiveness of medical treatments, such as intra-arterial injections that rely on accessing the bloodstream through these arteries. Hence, this present study analyses the behavior of blood flow and solute dispersion in an inclined artery while considering the Herschel-Bulkley model representing the blood rheology to investigate the influence of arterial inclination. The solutions for flow velocity and solute concentration are solved using the integration method. The Taylor-Aris method has been implemented to obtain effective axial and relative axial diffusion. This research investigates the impact of artery inclination on blood flow, solute dispersion characteristics (flow velocity, solute concentration, and axial diffusions), as well as explores the influence of gravitational acceleration on blood flow and solute dispersion behaviors. Results show that the angle of artery inclination directly influences the gravitational acceleration effect which correlates to the resulting flow velocity and solute dispersion. 90o and 270o inclination angle has the highest effect in increasing and decreasing the flow velocity, solute concentration and diffusions respectively. Meanwhile, 0o, 180o and 360o eliminate the gravitational acceleration effect on the flow behavior and dispersion process.

Research on the effect of yawing motion on tidal turbine performance based on actuator-line method

An actuator line method (ALM) code is used to investigate the yaw motion of tidal stream turbines, using different induced frequencies, amplitudes and starting angles. The relative velocity in the ALM calculation is corrected by considering the reaction force of the water on the floating tidal turbine. Because the ALM directly converts the flow velocity characteristics on the mesh element into the force characteristics, more small-scale and high-frequency signals appear, compared to Blade-Resolved Method simulations. In the results, the oscillation frequency of power coefficient and thrust coefficient (Cp, Ct) is twice of the yawing motion frequency when the starting yaw angle is 0°. Increasing the yawing amplitude as well as the starting angle both lower the mean values of Cp and Ct whilst the effect of frequency is slight. The turbine's hydrodynamic coefficients are obtained by best-fit model. The yawing amplitude has a moderate effect on the constant hydrodynamic terms.

Laboratory Models of Planetary Core-Style Convective Turbulence

The connection between the heat transfer and characteristic flow velocities of planetary core-style convection remains poorly understood. To address this, we present novel laboratory models of rotating Rayleigh–Bénard convection in which heat and momentum transfer are simultaneously measured. Using water (Prandtl number, Pr≃6) and cylindrical containers of diameter-to-height aspect ratios of Γ≃3,1.5,0.75, the non-dimensional rotation period (Ekman number, E) is varied between 10−7≲E≲3×10−5 and the non-dimensional convective forcing (Rayleigh number, Ra) ranges from 107≲Ra≲1012. Our heat transfer data agree with those of previous studies and are largely controlled by boundary layer dynamics. We utilize laser Doppler velocimetry (LDV) to obtain experimental point measurements of bulk axial velocities, resulting in estimates of the non-dimensional momentum transfer (Reynolds number, Re) with values between 4×102≲Re≲5×104. Behavioral transitions in the velocity data do not exist where transitions in heat transfer behaviors occur, indicating that bulk dynamics are not controlled by the boundary layers of the system. Instead, the LDV data agree well with the diffusion-free Coriolis–Inertia–Archimedian (CIA) scaling over the range of Ra explored. Furthermore, the CIA scaling approximately co-scales with the Viscous–Archimedian–Coriolis (VAC) scaling over the parameter space studied. We explain this observation by demonstrating that the VAC and CIA relations will co-scale when the local Reynolds number in the fluid bulk is of order unity. We conclude that in our experiments and similar laboratory and numerical investigations with E≳10−7, Ra≲1012, Pr≃7, heat transfer is controlled by boundary layer physics while quasi-geostrophically turbulent dynamics relevant to core flows robustly exist in the fluid bulk.

Transient Coupled Flow Model for Matrix-Fracture in High-Pressure Gas Reservoirs Opened by Gas Drilling

Gas drilling technology is an effective method to protect low permeability tight sandstone reservoirs from damage. However, using this technology to drill high-pressure fractured reservoirs, the fluid flow characteristics are extremely complex, leading to drilling safety challenges. Therefore, based on the conservation equations of mass, momentum, and energy, a new transient coupled flow model in matrix-fracture is established for high-pressure gas reservoirs opened by gas drilling, considering convection term and energy equation, to research the pressure and flow velocity transient behaviors. This model is solved by Shaher Momani’s algorithm and CyabJiBe format, and the type curves of the pressure and flow velocity are plotted. The three flow stages are developed, and the impact of parameters and equation terms on the transient flow behavior is analyzed and discussed, such as the energy equation, the matrix permeability ( k ), the fracture aperture ( L f ), and the fracture outlet pressure. It is found that the energy equation term of the model has a great influence on the transient characteristics such as velocity and pressure, which cannot be ignored. In the first flow stage, the flow velocity characteristics are not affected by the matrix parameters being extremely unstable, but in the second and third stages, the influence of the gas supplied to fracture cannot be ignored. The proposed transient coupled flow model provides a new understanding of the transient flow behavior in matrix-fracture for high-pressure reservoirs during gas drilling, which can be used to interpret the characteristics of pressure and velocity more realistically, to provide support for safe drilling of gas drilling.

Hemodynamic analysis of a curved artery based on microcirculation boundary.

Microcirculation plays a key role in regulating blood flow but is not considered in previous research of hemodynamics. A curved artery model is established to study its hemodynamic characteristics based on microcirculation boundary. The hemodynamic model of a curved artery is constructed and simulated by computational fluid dynamics. The curved artery model is simulated by fluid-structure interaction. At the same time, a porous medium is used to simulate microcirculation as the outlet boundary. The distribution characteristics of the blood flow velocity, the pressure and the wall shear stress in different sections at different time of the cardiac cycle are obtained. The results show that the velocities in curved arteries decrease and the pressures gradually increase. The blood flow velocity waveform and value are affected and they are sensitive to the microcirculation boundary. However, the pressure value is only affected by the microcirculation function. This work is useful for researchers to deeply understand the hemodynamic characteristics of curved arteries. There is important clinical significance to analyze the pathogenesis of cardiovascular disease considering microcirculation function and its coupling effect.

Chemical reaction and Soret effect on an unsteady MHD heat and mass transfer fluid flow along an infinite vertical plate with radiation and heat absorption

In the current investigation, it is anticipated to examine the influence of heat absorption and radiation on an unsteady transient MHD heat and mass transfer natural convective flow of an optically thin non-Grey Newtonian fluid through an abruptly started infinite vertical porous plate with ramped wall temperature and plate velocity in the presence of Soret and chemical reaction of the first order is solved precisely. Using the similarity variables, the governed PDE's are converted into dimensionless governing equations and they are solved numerically by employing the finite element technique. Numerical calculations and graphs are used to illustrate the important features of the solution on fluid flow velocity, heat, and mass transfer characteristics under different quantities of parametric circumstances entering into the problem. Moreover, we computed the physical variables such as the coefficient of drag force, rate of heat, and mass transfer. The findings indicate that when the thermal radiation parameter increases, the thermal boundary layer becomes thinner. To establish the veracity of our present results, we compared them to previously published research and found substantial concordance.

Verification of sap flow characteristics and measurement errors of Populus tomentosa Carr. and Salix babylonica L. based on the liquid level equilibrium method.

This study clarified the characteristics and influencing factors of sap flow in Populus tomentosa Carr. and Salix babylonica L., and verified the applicability of Granier’s original formula for measuring the sap flow of the two species, aimed to provide a basis for the accurate assessment of tree transpiration. P. tomentosa and S. babylonica were used as research objects, their sap flow was measured by the thermal dissipation probe method (TDP), together with changes in meteorological factors and soil water content. Meanwhile, the transpiration of both species was measured by the liquid level equilibrium method (LLE) to verify the applicability of Granier’s original formula. We found that: (1) the sap flow velocity of P. tomentosa and S. babylonica under typical sunny and cloudy conditions showed unimodal or bimodal changes, which were highly significantly correlated with meteorological factors (P < 0.01), but they were all small and poorly correlated with meteorological factors on rainy days. (2) The sap flow velocity of both species was significantly and negatively correlated (P < 0.05) with the daily change in stem and soil water content at 10–20 cm. (3) Compared to that calculated with the LLE method, the sap flows of the two species calculated by the TDP technique using Granier’s original formula were seriously underestimated, with error rates of -60.96% and -63.37%, respectively. The Granier’s correction formulas for P. tomentosa and S. babylonica established by the LLE method were Fd = 0.0287K1.236 (R2 = 0.941) and Fd = 0.0145K0.852 (R2 = 0.904), respectively, and the combined correction formula was Fd = 0.0235K1.080 (R2 = 0.957). It was verified that the errors of sap flow calculated by the specific correction formulas for P. tomentosa and S. babylonica were -6.18% and -5.86%, and those calculated by the combined correction formula were -12.76% and -2.32%, respectively. Therefore, the characteristics of the sap flow velocity of P. tomentosa and S. babylonica on sunny, cloudy and rainy days were different and significantly influenced by meteorological factors. The original Granier’s formula for calculating their sap flow resulted in a large error, but can be measured more accurately by constructing specific correction and combination formulas through the LLE method.

Probing the generation mechanism of emulsion based on shearing actions between multiphase fluids in porous media

The generation, migration, and coalescence processes of emulsions in porous media of the actual formations are relatively complex. However, few studies have been reported about the generation mechanism of emulsions under shearing action, especially under shearing action between multiphase fluids. In this paper, the concept of emulsification caused by fluid shearing was proposed for the first time. An oil-water two phases flow model in porous media was established to study the generation process of emulsion caused by shearing actions between oil and water. Fluid flow velocity, pressure and distribution characteristics of oil and water during this process were recorded. The effects of flow velocity and oil-water interface properties on the generation process of emulsion were investigated. Combined with the microscopic visualization oil displacement model, the generation characteristics of emulsions in porous media were further explored. The results indicated that the complex flow between oil and water in porous media would cause shear emulsification of crude oil. With the increase of flow velocity of oil-water two phases, the shear emulsification capacity was gradually enhanced. The generation capacity of emulsion in the micro shearing unit was mainly affected by the flow velocity of the displacing phase, and the particle size of the emulsion was mainly affected by the flow velocity of the shearing phase. When the interfacial tension between oil and water was lower than 10−1 mN/m, the shear emulsification rate did not change significantly. These results are of great significance for the supplement and improvement of the generation mechanism of emulsions in porous media, providing theoretical guidance for further enhancing oil recovery by regulating emulsification.

Three-dimensional smoothed particle hydrodynamics modeling of near-shore current flows over rough topographic surface

In this study, a three-dimensional (3D) numerical model based on the smoothed particle hydrodynamics (SPH) approach was developed to simulate the near-shore current flows over a rough topographic surface in the coastal area, where the flows are shallow and demonstrate strong turbulent characteristics. The numerical program is based on the open-source code SPHysics (http://www.sphysics.org), and two major improvements are made to treat the turbulence and rough boundary effects: A modified sub-particle-scale (SPS) eddy viscosity model is developed to address the turbulence transfer of flows, and a drag force equation is included in the momentum equations to account for the influence of roughness element on the bed and lateral boundaries. The computed results of flow velocity, shear stress, and free surface characteristics are compared with the laboratory measurements for a variety of test conditions. It has shown that the present SPH model can accurately simulate 3D-free surface near-shore current flows over a realistic topography with roughness.

Experimental and Numerical Study on the Dynamic and Flow Characteristics of a Reciprocating Pump Valve

The structure and dynamics of a reciprocating pump liquid end affect the volumetric efficiency and net positive suction head. To match the kinematics with theoretical parameters, reciprocating pump valve motion and flow visualization tests and computational fluid dynamics (CFD) analyses were performed on a wing-guided bevel discharge valve in a horizontal quintuple single-acting reciprocating pump. The valve motion test results showed that the maximum pump valve displacement and the pump valve opening and closing durations were approximately 8.3 mm, 29 ms, and 38 ms, respectively. The corresponding flow visualization test results were 11.4 mm, 9.5 ms, and 35.5 ms. The valve closing durations obtained from the valve motion and flow visualization tests are approximately twice as high as the U-Adolph prediction. The maximum displacement obtained from the valve motion test is consistent with the U-Adolph prediction. Three-dimensional CFD analyses were performed to investigate the flow states, pressure, and velocity characteristics of the discharge valve opening. Finally, the proposed method was applied to develop a new horizontal quintuple single-acting reciprocating pump with a rated flow rate of 1250 L/min and pressure of 40 MPa. This developed pump exhibited good performance and excellent reliability.

Sessile droplet evaporation in the atmosphere of different gases under forced convection

The phenomenon of evaporation from the surface of a liquid droplet into a neutral noncondensible gas was numerically studied by taking forced convection gaseous flow into account. The mathematical model considers the effects of surface tension, gravitational force, viscosity of both liquid and gaseous media, as well as the Stefan flow from the droplet surface, possible free gravitational convection, and the Marangoni convection in droplets, and it is designed to describe diffusion-limited evaporation. We consider the diffusion-limited evaporation process when the diffusive gas flux to the droplet surface is compensated by the convective Stefan flow from the surface. The results indicate an interaction of the liquid and gaseous media. Convective gas flows cause the liquid to move and a vortex to occur in the droplet. The flow velocities in a vortex are 103 times less than the characteristic velocity of forced convection flow in air. The droplet surrounded by gaseous flow changes its shape and oscillates, which causes a gas-density wave. Calculations have shown that the diffusion-limited evaporation rate does not change in the presence of forced convection, which contradicts most of the known experimental works. The possible reason for this discrepancy is the presence of non-equilibrium conditions at the liquid–gas interface in experiments. This leads to a consequent change of the evaporation mode to non-diffusive, while the numerical model postulates the Stefan condition and diffusion-limited evaporation.

Signal Conversion and Isolation Processing Technology Used in the Cerebrovascular Stroke Detector

By using Doppler sensor and pressure sensor, the cerebrovascular stroke detector can be used to measure the blood flow velocity and blood pressure of the carotid artery. In this study, a variety of signal conversion and isolation processing techniques are proposed for processing and feature extraction of the output signals from the sensors. Finally, effective signal output waveforms that can be used to evaluate the cerebrovascular hemodynamics index (CVHI) are obtained, and the sound signal outputs that can reflect the change characteristics of blood flow velocity and blood pressure signals are generated, which realizes the application functional requirements of the detector.

Effect of gas compressibility on fluid field of air‐cooled turbo‐generator

The effect of gas compressibility on the fluid flow characteristics of a 350 MW air-cooled turbo-generator is investigated in this paper. Two gas models taking gas compressibility and incompressibility into account are established for numerical calculation. Then, a one-fourth physical model based on the practical ventilation structure and basic assumption is built to analyse the flow velocity and flow rate using the finite volume method (FVM). The FVM-predicted flow rate and flow velocity of cooling medium in the air cavity, stator and rotor of the generator show the distribution characteristics of flow rate and velocity in the generator is affected by the gas compressibility model selection. The comparison of FVM-predicted flow rate and experimental value shows that the FVM-predicted results using the gas compressibility model is more accurate when comparing to those using the incompressible model. Therefore, the gas compressibility model is an appealing approach to analyse the flow fluid characteristics of the air-cooled turbo-generator.

Horizontal flame spread over thin solids in reduced buoyancy environments

A Horizontal Channel Apparatus (HCA) has been employed to investigate opposed flame spread over solid fuels in reduced buoyancy environments, which would be encountered at the diminished gravitational levels on extraterrestrial surfaces (e.g., the partial gravity on the Moon and Mars) as well. With a scaling analysis, the characteristic buoyant flow velocity in HCA is well correlated to the channel height and the Rayleigh (Ra) number. The experimental results show that, without forced flow, the flame spread rate and flammability in HCA can be correlated with those at different gravity levels by using Ra number, indicating HCA may have the ability to simulate the burning characters in partial gravity. Together with the Reynolds (Re) and Ra numbers, which signify the role of forced and buoyant flow, respectively, the flame spread rates and the map of flammability of the solid fuel obtained in the current HCA experiments are determined. Furthermore, four distinctively different flame spread patterns are found at various channel heights and opposed-flow velocities once the width of the cellulosic sample is extended. Likewise, the map of flame spread patterns is governed by the Re and Ra. It is further found through the examinations of the time average of the mass-loss rate that as long as Ra is below a critical value, the opposed flow in terms of Re mainly determines the oxygen transportation, while the reduced buoyancy in terms of Ra mainly contributes to the bifurcations of the potential hydro/thermal instabilities.

A Spatiotemporal Model for the Effects of Toxicants on Populations in a Polluted River

One reason why polluted water is the growing global concern is because it persists to pose threats to the health of aquatic life. To study the effects of environmental toxicants on population dynamics in polluted rivers, we develop a process-oriented model that describes the interaction between a population and a toxicant in an advective environment. The model consists of two reaction-diffusion-advection equations, one of which governs the dispersal and growth of the population under the influence of toxicants, while the other describes the dispersal, input, as well as decay of the toxicant. We explore the existence and stability of steady states based on the analysis of eigenvalue problems, which yields sufficient conditions that lead to population persistence or extinction. We numerically analyze how the interplay between several factors (toxicant input, flow velocity, the diffusion and advection characteristics of the population and the toxicant) affects the persistence and spatial distribution of the population.

Characteristics of Peripheral Blood Flow Velocity According to the Therapeutic Effect of Spinal-centered Personal Warmer

Characteristics of Peripheral Blood Flow Velocity According to the Therapeutic Effect of Spinal-centered Personal Warmer

Modeling Spatial Patterns of Dissolved Oxygen and the Impact Mechanisms in a Cascade River

Dissolved oxygen (DO) concentration is an essential indicator for assessment of river ecosystems. A hydrodynamic and water quality mathematical model coupling one-dimensional and two-dimensional models is developed in this study. The characteristics of study area, flow velocity, temperature, and organic contamination are taken as consideration in the scenario setting. The changing processes of DO concentration are simulated in different scenarios, and the effects on DO concentration are discussed. Results indicate that: 1) A negative relation was present between DO concentration in Yongjiang River and releasing discharge of the Laokou hydro-project, since reoxygenation is greater than oxygen consumption along the river, DO concentration increases from upstream to downstream. 2) DO concentration increases with the releasing of DO in the water, which also varies along with the releasing of biochemical oxygen demand (BOD) concentration. Laokou exhibits the greatest increase of BOD, which ranges from 0.1 mg/L to 0.75 mg/L 3) The increasing of water temperature results in increased reoxygenation and a decrease in oxygen consumption. Our study shows that the water temperature increased from 19°C to 29 °C, and correspondingly saturated DO decreased from 9.25 mg/L to 7.54 mg/L. The study provides scientific support for ecology operation in the cascade river, and is expected to improve the water environment by reservoir regulation.

Characteristics of the descending genicular artery blood flow velocity in patients with knee osteoarthritis

BackgroundIn patients with knee osteoarthritis (KOA), the descending genicular artery (DGA) showed abnormal angiogenesis. However, the non-invasive assessment method of DGA remains unclear. The aim of this study was to clarify the characteristics of blood flow velocity of the DGA in patients with KOA and to examine the factors involved in the changes. MethodsThe KOA group included 22 knees of 22 patients with KOA (4 males, 18 females; mean age, 72.3 ± 7.5 years) and the control group included 22 knees (4 males, 18 females; mean age, 71.3 ± 5.4 years) of 22 healthy adults. The peak systolic blood flow velocity (PSV) in each group was measured using ultrasonography. The KOA group was classified into the effusion group and the non-effusion group based on observed effusion, and the PSV was compared between the two groups. The relationships between PSV and suprapatellar bursa intracavitary distance, pain, femorotibial angle, Japanese Knee Osteoarthritis Measure were also investigated. ResultsThe PSV in the KOA group (51.5 ± 12.9 cm/s) was significantly higher than that in the control group (29.3 ± 4.4 cm/s) (P < 0.01). In the KOA group, PSV in the effusion group (55.5 cm/s (51.2–59.4 cm/s)) was significantly higher than that in the non-effusion group (39.1 cm/s (35.1–44.4 cm/s)) (P < 0.01). The PSV was positively and significantly correlated with both suprapatellar bursa intracavitary distance (r = 0.81: P < 0.01) and pain (r = 0.48: P < 0.05). ConclusionsThe PSV measurement in the DGA is useful for the evaluation of non-invasive synovitis of patients with KOA.

Experimental Study of Flow Characteristics in A Rectangular Gravel Bed Channel

In an open channel flow, the characteristics of flow resistance are greatly affected by the roughness of the base and the walls of the channel. The existence of an object or other material, including gravel, also influenced the resistance of flow, therefore the purpose of this study is to examine the flow characteristics (flow velocity and flow resistance) in gravel open channel by using experimental study. A laboratory study to explore the effect of channel bed in terms of roughness of types of sediment on the hydraulics flow in 8 m length x 40 cm width a rectangular channel is presented. The study consists of an extensive set of rectangular flume experiments for flows with certain slope and sediment bed. The study was using the Before After Control Impact (BACI) method by set up five different scenarios. The results show that the lowest flow velocity (v=0.3041 m/sec) was occurred in the scenario 3 (50%sand and 50% gravel). Based on the Manning’ coefficient (n), it was also found that at the 100% discharge flow condition, the highest value of friction factor (f=0.0780) within 5 scenarios was scenario 3 with the sediment consisted of 50%sand and 50%gravel. Whereas the value of the lowest friction factor(f=0.0652) was scenario 1 with the sediment only gravel within. It concluded that the results gave the lower value of Manning’ coefficient (n) compared to the table of Manning’s coefficient (f= 0.04) for the channel with gravel base condition.