Maximum Jet Velocity Research Articles

Steady Flow Hemodynamic and Energy Loss Measurements in Normal and Simulated Calcified Tricuspid and Bicuspid Aortic Valves

The bicuspid aortic valve (BAV), which forms with two leaflets instead of three as in the normal tricuspid aortic valve (TAV), is associated with a spectrum of secondary valvulopathies and aortopathies potentially triggered by hemodynamic abnormalities. While studies have demonstrated an intrinsic degree of stenosis and the existence of a skewed orifice jet in the BAV, the impact of those abnormalities on BAV hemodynamic performance and energy loss has not been examined. This steady-flow study presents the comparative in vitro assessment of the flow field and energy loss in a TAV and type-I BAV under normal and simulated calcified states. Particle-image velocimetry (PIV) measurements were performed to quantify velocity, vorticity, viscous, and Reynolds shear stress fields in normal and simulated calcified porcine TAV and BAV models at six flow rates spanning the systolic phase. The BAV model was created by suturing the two coronary leaflets of a porcine TAV. Calcification was simulated via deposition of glue beads in the base of the leaflets. Valvular performance was characterized in terms of geometric orifice area (GOA), pressure drop, effective orifice area (EOA), energy loss (EL), and energy loss index (ELI). The BAV generated an elliptical orifice and a jet skewed toward the noncoronary leaflet. In contrast, the TAV featured a circular orifice and a jet aligned along the valve long axis. While the BAV exhibited an intrinsic degree of stenosis (18% increase in maximum jet velocity and 7% decrease in EOA relative to the TAV at the maximum flow rate), it generated only a 3% increase in EL and its average ELI (2.10 cm2/m2) remained above the clinical threshold characterizing severe aortic stenosis. The presence of simulated calcific lesions normalized the alignment of the BAV jet and resulted in the loss of jet axisymmetry in the TAV. It also amplified the degree of stenosis in the TAV and BAV, as indicated by the 342% and 404% increase in EL, 70% and 51% reduction in ELI and 48% and 51% decrease in EOA, respectively, relative to the nontreated valve models at the maximum flow rate. This study indicates the ability of the BAV to function as a TAV despite its intrinsic degree of stenosis and suggests the weak dependence of pressure drop on orifice area in calcified valves.

Accurate Assessment of Aortic Stenosis

Aortic valve (AV) stenosis is one of the most common valvular diseases and is the third most common cardiovascular disease in developed countries. It occurs in ≈2.8% of patients ≥75 years of age and can occur because of degenerative calcification and congenital valvular defects such as bicuspid AVs or rheumatic disease.1–3 Calcific aortic stenosis (AS) is associated with increased leaflet stiffness and a narrowed AV orifice, resulting in increased pressure gradients across the valve. The presence of a bicuspid AV significantly increases the risk of AS.4 The natural history of AS is a prolonged asymptomatic period, with progressive reduction of the AV orifice area due to sclerosis initially, culminating in calcific AS. This is accompanied by a corresponding increase in the transaortic pressure gradient (Δ P ) and myocardial pressure overload. Through the preload reserve, the left ventricle (LV) compensates for the increased workload until the sarcomeres stretch to their maximum diastolic length. Once the preload reserve is exhausted, increases in afterload are accompanied by a reduction in stroke volume (SV), resulting in afterload mismatch. Ultimately, this causes LV hypertrophy, associated with an enlargement of cardiac myocytes and increased LV wall thickness.5 Initial diagnosis of AS typically occurs during routine physical examination with the presence of a heart murmur, click, or other abnormal sounds, but undiagnosed patients may experience the onset of severe symptoms such as angina, syncope, and heart failure. Without intervention, patient mortality typically occurs within 5 years of the onset of symptoms.6–11 Multiple studies and reviews have focused on the clinical aspects of this disease, including disease progression, markers of disease severity, treatment guidelines, and outcomes.1–3,6,12–16 Very few reviews have focused on the hemodynamic principles underlying AS and on comparing data obtained across different …

Experimental Characterization of the Plasma Synthetic Jet Actuator

The plasma synthetic jet is a novel active flow control method because of advantages such as fast response, high frequency and non-moving parts, and it has received more attention recently, especially regarding its application to high-speed flow control. In this paper, the experimental characterization of the plasma synthetic jet actuator is investigated. The actuator consists of a copper anode, a tungsten cathode and a ceramic shell, and with these three parts a cavity can be formed inside the actuator. A pulsed-DC power supply was adopted to generate the arc plasma between the electrodes, through which the gas inside was heated and expanded from the orifice. Discharge parameters such as voltage and current were recorded, respectively, by voltage and current probes. The schlieren system was used for flow visualization, and jet velocities with different discharge parameters were measured. The schlieren images showed that the strength of plasma jets in a series of pulses varies from each other. Through velocity measurement, it is found that at a fixed frequency, the jet velocity hardly increases when the discharge voltage ranges from 16 kV to 20 kV. However, with the discharge voltage fixed, the jet velocity suddenly decreases when the pulse frequency rises above 500 Hz, whereas at other testing frequencies no such decrease was observed. The maximum jet velocity measured in the experiment was up to 110 m/s, which is believed to be effective for high-speed flow control.

Parametric Analysis of Turbulent Wall Jet in Still Air Over a Transitional Rough, With Asymptotes of Fully Rough and Fully Smooth Wall Jets

The novel scalings for streamwise variations of the flow in a turbulent wall jet over a fully smooth, transitional, and fully rough surfaces have been analyzed. The universal scaling for arbitrary wall roughness is considered in terms of the roughness friction Reynolds number (that arises from the stream wise variations of roughness in the flow direction) and roughness Reynolds number at the nozzle jet exit. The transitional rough wall jet functional forms have been proposed, whose numerical constants power law index and prefactor are estimated from best fit to the data for several variables, like, maximum wall jet velocity, boundary layer thickness at maxima of wall jet velocity, the jet half width, the friction factor and momentum integral, which are supported by the experimental data. The data shows that the two asymptotes of fully rough and fully smooth surfaces are co-linear with transitional rough surface, predicting same constants for any variable of flow for full smooth, fully rough and transitional rough surfaces. There is no universality of scalings in terms of traditional variables as different expressions are needed for each stage of the transitional roughness. The experimental data provides very good support to our universal relations.

G051016 半円周りの流れ場に対するシンセティツクジェツトの多目的最適化([G051-01]流体工学部門,一般セッション : 流体力学の機器への応用)

The control parameters for a synthetic jet acting on a separated flow over hump are optimized using multi-objective optimization and effects of separation control are discussed. The following three parameters are used for operation of a synthetic jet: a synthetic jet position, a maximum velocity of jet and a synthetic jet frequency. A direct numerical simulation is performed by solving compressible, unsteady, laminar flows over a half cylindrical hump in two dimensions, and effectiveness of each operation of a synthetic jet is investigated. The optimization results show that periodic actuation improves aerodynamic coefficients. In particular, the performance of the synthetic jet placed around the top of the hump is better than other positions. It is found that the lift coefficient is maximized when a synthetic jet act at a low frequency in forward. Also it is found that the drag coefficient is minimized when a synthetic jet act at a high frequency in backward.

Momentum Coefficient as a Parameter for Aerodynamic Flow Control with Synthetic Jets

The influence of periodic excitation from synthetic jet actuators on boundary-layer separation and reattachment over a NACA 0025 airfoil at a low Reynolds number is studied. Flow-visualization results showed a vertical jet pulse accompanied by two counter-rotating vortices being produced at the exit of the simulated slot, with the vortices shed at the excitation frequency. Hot-wire measurements determined the maximum jet velocity for a range of excitation frequencies and voltages, and were used to characterize the excitation amplitude in terms of the momentum coefficient . With the synthetic jet actuator installed in the airfoil, flow-visualization results showed that excitation produces boundary-layer reattachment, with the associated significant reduction in wake width. Wake-velocity measurements were performed to characterize the effect of flow-control excitation amplitude and frequency on airfoil drag and wake topology. The results demonstrate that is the primary governing flow-control parameter. Applying excitation above a specific threshold produced a 50% reduction in drag, significantly affecting wake topology. However, power consumption of a piezoelectric synthetic jet actuator depends substantially on the excitation frequency. Hence, by varying excitation frequency, significant gains in efficiency are possible.

High‐speed flow erosion test study on roller compacted concrete dam during construction

PurposeA new roller compacted concrete dam of Fengman hydropower station was determined to be built in the toe of the old dam which had been identified as a dangerous dam. The new dam during construction would be impacted by the high‐speed flow discharged from the old dam. This is an important problem met for the first time in China, which would affect the whole project construction. The purpose of this paper is to describe a series of erosion experiments of the new dam material.Design/methodology/approachA kind of high‐speed flow erosion test apparatus was developed for erosion experiment of the new dam material. The maximum jet velocity was up to 40 m/s and the section area of the nozzle was 25 cm2. In the process of experiments, the equipment showed its good performance. Erosive wear tests of two types of materials used in the new dam, a roller compacted concrete and a distorted concrete with four kinds of ages were carried out with the flow velocity in the range of 30‐35 m/s.FindingsErosion parameters and erosion laws of the two types of concretes with different ages were obtained, and a general relationship had been found between erosion rate and flow velocity: with velocity exponent between 3.33 and 3.93. It was also concluded that the erosion resistance of the distorted concrete was better than that of the roller compacted concrete and the mechanics properties of the concretes of over 14 days age was influenced slightly by water impacted.Originality/valueThe test results would play a practical technique guide role for the safety of this project during construction in the flood season.

Collapse of micrometer-sized cavitation bubbles near a rigid boundary

The interaction of cavitation bubbles with a rigid boundary and its dependence on the distance between bubble and boundary is investigated experimentally. Individual cavitation bubbles, with a maximum radius of 150 μm, are generated by using pulsed high-intensity focused ultrasound. Observations are made with high-speed photography with framing rates of up to 200 million frames per second and exposure time of 5 ns, and the spatial resolution is in the order of a few micrometers. The significant parameter of this study is the non-dimensional stand-off parameter, γ, defined as the distance between the ultrasound focus and the rigid boundary scaled by the maximum bubble radius. Both the velocity of the liquid jet developed during bubble collapse and the maximum pressure of the shock wave emitted during bubble rebound show a minimum for γ ≈ 1 and a constant value for γ > 3. The maximum jet velocity is slightly smaller than the corresponding values obtained in the case of millimeter-sized bubbles and ranges from 80 m/s (at γ ≈ 1) to 130 m/s (for γ > 3). No jet formation was observed for γ > 3. The shock wave pressure, measured at a distance of 5 mm from the emission center, ranges from 0.2 MPa (at γ ≈ 1) to 0.65 MPa (for γ > 3). These values are an order of magnitude smaller than those obtained in the case of millimeter-sized bubbles. The shock wave duration is almost independent of γ at a value of about 75 ns. For large γ values (γ > 3), a large percentage of the bubble energy (up to 60 %) is transformed into the mechanical energy of the shock wave emitted during bubble rebound but, for γ ≈ 1, the conversion efficiency decreases to 30 %. Independent of the relative distance between bubble and rigid boundary, the shock pressure decays proportionally to r−1 with increasing distance r from the emission center. The results are discussed with respect to cavitation damage and collateral effects in pulsed high-intensity focused ultrasound surgery.

Visualization of Supersonic Non-Newtonian Liquid Jets

This paper describes the characteristics of supersonic non-Newtonian liquid jets injected in ambient air. The main focus is to visualize three types of time-independent non-Newtonian liquid jet and to describe their behaviors. Moreover, comparisons between their dynamic behaviors with Newtonian liquid jet are reported. The supersonic liquid jets are generated by impact driven method in a horizontal single-stage power gun. Jets have been visualized by the high speed digital video camera and shadowgraph method. Effects of different liquid types on the jet penetration distance, average jet velocity and other characteristics have been examined. From shadowgraph images, the unique dynamic behaviors of each non-Newtonian liquid jets are observed and found obviously different from that of the Newtonian liquid jet. The maximum average jet velocity of 1,802.18 m/s (Mach no. 5.30) has been obtained. The jet penetration distance and average velocity are significantly varied when the liquid types are different.

Effect of vehicle configuration on the performance of a submersible pulsed-jet vehicle at intermediate Reynolds number

Recent results have demonstrated that pulsed-jet propulsion can achieve propulsive efficiency greater than that for steady jets when short, high frequency pulses are used, and the pulsed-jet advantage increases as Reynolds number decreases into the intermediate range (∼50). An important aspect of propulsive performance, however, is the vehicle configuration. The nozzle configuration influences the jet speed and, in the case of pulsed-jets, the formation of the vortex rings with each jet pulse, which have important effects on thrust. Likewise, the hull configuration influences the vehicle speed through its effect on drag. To investigate these effects, several flow inlet, nozzle, and hull tail configurations were tested on a submersible, self-propelled pulsed-jet vehicle (‘Robosquid’ for short) for jet pulse length-to-diameter ratios (L/D) in the range 0.5–6 and pulsing duty cycles (StL) of 0.2 and 0.5. For the configurations tested, the vehicle Reynolds number (Reυ) ranged from 25 to 110. In terms of propulsive efficiency, changing between forward and aft-facing inlets had little effect for the conditions considered, but changing from a smoothly tapered aft hull section to a blunt tail increased propulsive efficiency slightly due to reduced drag for the blunt tail at intermediate Reυ. Sharp edged orifices also showed increased vehicle velocity and propulsive efficiency in comparison to smooth nozzles, which was associated with stronger vortex rings being produced by the flow contraction through the orifice. Larger diameter orifices showed additional gains in propulsive efficiency over smaller orifices if the rate of mass flow was matched with the smaller diameter cases, but using the same maximum jet velocity with the larger diameter decreased the propulsive efficiency relative to the smaller diameter cases.

Effects of chamber temperature and pressure on the characteristics of high speed diesel jets

This study is an investigation into the effects of temperature and pressure within a test chamber on the dynamic characteristics of injected supersonic diesel fuel jets. These jets were generated by the impact of a projectile driven by a horizontal single stage powder gun. A high speed video camera and a shadowgraph optical system were used to capture their dynamic characteristics. The test chamber had controlled air conditions of temperature and pressure up to 150 °C and 8.2 bar, respectively. It was found experimentally that, at the highest temperature, a maximum jet velocity of around 1,500 m/s was obtained. At this temperature, a narrow pointed jet appeared while at the highest pressure, a thick, blunt headed jet was obtained. Strong shock waves were generated in both cases at the jet head. For analytical prediction, equations of jet tip velocity and penetration from the work of Dent and of Hiroyasu were employed to describe the dynamic characteristics of the experiments at a standard condition of 1 bar, 30 °C. These analytical predictions show reasonable agreement to the experimental results, the experimental trend differing in slope because of the effect of the pressure, density fluctuation of the injection and the shock wave phenomena occurring during the jet generation process.

Longitudinal variation and waves in Jupiter’s south equatorial wind jet

A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5°S planetographic latitude shows variations in velocity with longitude and time. The presence of the large anticyclonic South Equatorial Disturbance (SED) has a profound effect on the chevron velocity, causing slower velocities to its east and increasing with distance from the disturbance. The chevrons move with velocities near the maximum wind jet velocity of ∼140m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7°N latitude. Their repetitive nature is consistent with a gravity-inertia wave (n=75–100) with phase speed up to 25m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, for the first time, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a 6.7±0.7-day period. This oscillating motion has a wavelength of ∼20° and a speed of 101±3m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it. All dates show chevron latitude variability, but it is unclear if this larger wave is present during other epochs, as there are no other suitable time series movies that fully delineate it. In the presence of multiple wave modes, the difference in dominant cloud appearance between 7°N and 7.5°S is likely due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.

High-speed flow erosion on a new roller compacted concrete dam during construction

A new roller compacted concrete dam of Fengman Hydropower Station is to be built in the toe of the old dam, which was identified as a dangerous dam. The new dam during construction would be influenced by the high-speed flow discharged from the old dam, which is an important problem to be considered for the first time in China, and which would affect the construction of the whole project. Therefore, a series of erosion experiments were conducted in this article. A high-speed flow erosion test apparatus was developed for the erosion experiments of the new dam materials. The maximum jet velocity goes up to 40 m/s and the section area of the nozzle is 0.0025 m2. In the process of experiments, the equipment shows a good performance. Erosive wear tests for two types of materials used in the new dam, a roller compacted concrete and a distorted concrete with four kinds of ages were carried out with the flow velocity in the range of 30 m/s-35 m/s. Erosion parameters and erosion laws for the two types of concretes with different ages were determined, and a general relationship between the erosion rate and the flow velocity is obtained as: N = cvP, with the velocity exponent P between 3.33 and 3.93. It is concluded that the erosion resistance of the distorted concrete is better than that of the roller compacted concrete and the mechanical properties of the concretes of over 14 d age are influenced slightly by the water impact. The test results might serve as a practical technique guide for the safety of this project during its construction in the flood season.

Spray Atomization and Structure of Supersonic Liquid Jet with Various Viscosities of Non-Newtonian Fluids

These experimental investigations are designed to study shock wave characteristics and spray structure. Supersonic liq- uid jets injected into ambient fields are empirically studied using projectile impacts in a two-stage light gas gun. This study looks primarily at the design of the nozzle assembly, the tip velocity of the high speed jet, the structure of the spray jet and the shock wave generation process. The supersonic liquid jets were visualized using an ultra high-speed camera and the schlieren system for visualization to quantitatively analyze the shock wave angle. The experimental re- sults with straight cone nozzle types and various non-Newtonian fluid viscosities are presented in this paper. The effects of nozzle geometry on the jet behavior are described. The characteristics of the shock wave generation and spray jet structure were found to be significantly related to the nozzle geometry. The expansion gases accelerated the projectile, which had a mass of 6 grams, from 250 m/s. As a result, it was found that the maximum jet velocity appeared in the liquid jet with high viscosity properties. Supersonic liquid jets, which occurred at the leading edge the shock waves and the compression waves in front of the jets, were observed. Also, the shock waves significantly affected the atomization process for each spray droplet.

Groove angle effect on micro-jet from shocked metal surface

According to smoothed particle hydrodynamics, we investigate numerically the micro-jets from grooved surfaces of different metals, where the velocities of jet head and material sources are discussed in detail. Our simulation results suggest that the jetting factor reaches its maximum at the half angle 45 degree, and the jetting factor reduces with the increase or decrease of the groove angle; also, the maximum velocity of jet shows a linear reduction with the increase of groove angel. Those results are consistent with the corresponding experimental results. The jetting material source and its dynamical process are analyzed. It is shown that with the increase of groove angel, the jet material sources transfer to the bottom of groove from two-side layer, while at the groove angel near 45 degree, a homogenous source layer throughout the groove comes into being. Finally, we further explain the jetting dynamics from different grooves by particle trajectory and its mechanical quantity history.

Clinical outcomes in non-surgically managed patients with very severe versus severe aortic stenosis

ObjectiveThe management of asymptomatic severe and very severe aortic stenosis (AS) remains unestablished. This study aimed to investigate the clinical outcomes of severe versus very severe AS patients.DesignA single centre,...

Experimental characterization of an argon laminar plasma jet at atmospheric pressure

This paper deals with a dc laminar pure argon plasma jet operating at atmospheric pressure in ambient air that was experimentally studied in order to obtain temperature and velocity. Plasma jet temperature was evaluated by optical emission spectroscopy and the plasma jet velocity was determined by various methods using a pressure sensor. It is shown that the maximum plasma jet temperature is 15 000 K and the maximum plasma jet velocity is 250 m s−1 at the plasma jet centre. Finally, a study of the ambient air amount entrained into the plasma jet is presented.

Analysis of a Power Law and Log Law for a Turbulent Wall Jet Over a Transitional Rough Surface: Universal Relations

The power law and log law velocity profiles and an integral analysis in a turbulent wall jet over a transitional rough surface have been proposed. Based on open mean momentum Reynolds equations, a two layer theory for large Reynolds numbers is presented and the matching in the overlap region is carried out by the Izakson-Millikan-Kolmogorov hypothesis. The velocity profiles and skin friction are shown to be governed by universal log laws as well as by universal power laws, explicitly independent of surface roughness, having the same constants as a fully smooth surface wall jet (or fully rough surface wall jet, as appropriate). The novel scalings for stream-wise variations of the flow over a rough wall jet have been analyzed, and best fit relations for maximum wall jet velocity, boundary layer thickness at maxima of wall jet velocity, the jet half width, the friction factor, and momentum integral are supported by the experimental data. There is no universality of scalings in traditional variables, and different expressions are needed for transitional roughness. The experimental data provides very good support to our universal relations proposed in terms of alternate variables.

Treatment Options in Severe Aortic Stenosis

Case presentation: An 80-year-old woman is referred for cardiovascular evaluation because of a systolic murmur. She denies symptoms of angina, syncope, or heart failure. The physical examination and echocardiogram are consistent with severe aortic stenosis (AS). What further evaluation is indicated? Aortic stenosis is becoming more frequent as the average age of the population increases; it affects up to 5% of the elderly population.1 The diagnosis of severe AS is most easily defined by Doppler echocardiography with maximum aortic jet velocity >4.0 m/s, mean transvalvular pressure gradient >40 mm Hg, and continuity equation valve area <1.0 cm2 or valve area index <0.6 cm2 (Figure 1).2 However, when cardiac output is low, a lower transvalular gradient and jet velocity may be present. Echocardiography is also used in patients with AS to assess left ventricular hypertrophy, size, and function; left atrial size, and the presence of pulmonary hypertension or other associated valvular disease. Nevertheless, the decision to proceed with aortic valve replacement (AVR) is usually based on the presence of symptoms. So, if this patient really is asymptomatic, the echocardiographic criteria for severe AS would not automatically result in a cardiac surgery referral.3–5 Figure 1. Management strategy for patients with severe aortic stenosis. AVA indicates aortic valve area; BP, blood pressure; CABG, coronary artery bypass graft surgery; echo, echocardiography; LV, left ventricular; and Vmax, maximal velocity across aortic valve by Doppler echocardiography. Reprinted from Bonow et al2 with permission of the publisher. Copyright © 2008, the American Heart Association. The 1%/y risk of sudden death in asymptomatic patients with AS is not higher than that of historical controls without AS.5 However, because patients may deny or fail to recognize symptoms or avoid them by decreasing physical activity, exercise testing can be useful in asymptomatic …

Effect of Stand-Off Distance on Impact Pressure of High-Speed Water Jet Injected in Water

This study is to measure the impact pressure of high-speed water jet injected in water at the stand-off distance from the nozzle exit. The high-speed water jets are generated by the impact of a projectile, which known as impact acceleration method, launched by Horizontal Single Stage Power Gun. The maximum averaged jet velocity of about 374.24 m/s in water was generated in this experiment. The impact pressure of high-speed water jet in water at the stand-off distance 15, 20, 30 and 40 mm from the nozzle exit was measured by the PVDF pressure sensor. Moreover, the impact phenomena of the jet were visualized by a high-speed video camera with shadowgraph optical arrangement. From the pressure sensor, two peak over-pressures are always observed in this experiment. From visualization, it was found that the two peak over-pressures of 24 GPa and 35 GPa at x = 15 mm were generated by the jet and the bubble impact, respectively. The peak over-pressure decreases exponentially as the stand-off distance between the PVDF pressure sensor to the nozzle exit increases. Moreover, the jet and the bubble impact on the PVDF pressure sensor, shock waves, and bubble deformation were obviously observed in this study.