scholarly journals Comparisons of flow dynamics of dual-blade to single-blade beveled-tip vitreous cutters

2021 ◽  
Author(s):  
Makoto Inoue ◽  
Takashi Koto ◽  
Akito Hirakata
Keyword(s):  
Salt Solution ◽  
High Speed ◽  
Lateral View ◽  
Flow Dynamics ◽  
High Speed Camera ◽  
Mean Flow ◽  
Cutting Rate ◽  
The Mean ◽  
Fluorescent Polymer ◽  
End Results

Introduction: To compare the flow dynamics of the dual-blade to the single-blade beveled-tip vitreous cutters. Methods: The aspiration rates of balanced salt solution (BSS) and swine vitreous were measured for the 25-gauge and 27-gauge dual- and single-blade vitreous cutters. The flow dynamics of BSS and diluted vitreous mixed with fluorescent polymer at the maximal cutting rates and the reflux of BSS were measured in images obtained by a high-speed camera. The distal end of the cutter was defined as the head end. Results: The aspiration rates of BSS and vitreous by the 25- and 27-gauge dual-blade cutters were significantly higher than those of both single-blade cutters at the maximal cutting rate (all P≤0.01). The mean aspiration flow of BSS in front of the port from a lateral view was significantly faster for both dual-blade cutters than for both single-blade cutters (P=0.003, P=0.019). The angle of the mean flow of BSS of both dual-blade cutters was from the distal end (P<0.001, P<0.001) but that of the single blade-cutters was from the proximal end. The velocity and angle of the mean reflux flow of both types of cutters were not significantly different. The mean aspiration flow of diluted vitreous was significantly faster for 25-gauge dual-blade cutters with the angle more from the proximal end and 27-gauge dual-blade cutters more from the distal end than both single-blade cutters (P=0.018, P=0.048). Conclusion: The dual-blade beveled-tip vitreous cutters improve the efficiency of the vitrectomy procedures and maintain the distal aspirating flow by the beveled-tip.

scholarly journals Modeling the Excess Velocity of Low-Viscous Taylor Droplets in Square Microchannels

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 162 ◽  
Author(s):  
Thorben Helmers ◽  
Philip Kemper ◽  
Jorg Thöming ◽  
Ulrich Mießner
Keyword(s):  
High Speed ◽  
Process Intensification ◽  
Continuous Phase ◽  
Channel Cross Section ◽  
Optimization Approach ◽  
Mean Flow ◽  
Bypass Flow ◽  
Wall Film ◽  
Proposed Model ◽  
The Mean

Microscopic multiphase flows have gained broad interest due to their capability to transfer processes into new operational windows and achieving significant process intensification. However, the hydrodynamic behavior of Taylor droplets is not yet entirely understood. In this work, we introduce a model to determine the excess velocity of Taylor droplets in square microchannels. This velocity difference between the droplet and the total superficial velocity of the flow has a direct influence on the droplet residence time and is linked to the pressure drop. Since the droplet does not occupy the entire channel cross-section, it enables the continuous phase to bypass the droplet through the corners. A consideration of the continuity equation generally relates the excess velocity to the mean flow velocity. We base the quantification of the bypass flow on a correlation for the droplet cap deformation from its static shape. The cap deformation reveals the forces of the flowing liquids exerted onto the interface and allows estimating the local driving pressure gradient for the bypass flow. The characterizing parameters are identified as the bypass length, the wall film thickness, the viscosity ratio between both phases and the C a number. The proposed model is adapted with a stochastic, metaheuristic optimization approach based on genetic algorithms. In addition, our model was successfully verified with high-speed camera measurements and published empirical data.

MEAN FLOW OF A VERTICALLY VIBRATED HOURGLASS

1993 ◽  
Vol 07 (09n10) ◽  
pp. 1799-1805 ◽  
Author(s):  
Pierre EVESQUE ◽  
Wahib MEFTAH
Keyword(s):  
Time Constant ◽  
Flow Rate ◽  
Flow Dynamics ◽  
Mean Flow ◽  
Resonance Domain ◽  
The Mean ◽  
Vertical Vibrations

We have investigated the mean flow of a hourglass submitted to vertical vibrations as function of the amplitude a and frequency f=Ω/2π of the vibration (5Hz≤f≤100Hz) . We find that the time constant of the flow dynamics is longer than 0.2s, that the flow rate is weakly sensitive to vibrations as far as these ones have a small enough amplitude (aΩ2<g=10m/s2) . When aΩ2 becomes larger than g and when the frequency is located inside a resonance domain (10Hz<f<80Hz) , the flow rate decreases strongly; it even stops at large aΩ2 and when 40Hz<f<60Hz .

scholarly journals Stability, spatial extension and extinction of an electric arc in aeronautical conditions of pressure under 540 V DC

2019 ◽  
Vol 87 (3) ◽  
pp. 30901
Author(s):  
Romaric Landfried ◽  
Mohamed Boukhlifa ◽  
Thierry Leblanc ◽  
Philippe Teste ◽  
Jonathan Andrea
Keyword(s):  
High Speed ◽  
Electric Arc ◽  
High Speed Camera ◽  
Arc Length ◽  
Electrode Gap ◽  
Arc Current ◽  
The Mean ◽  
The Stability ◽  
Energy Dissipated

This work deals with the characterization of DC electric arcs in aeronautical conditions of pressure (from 104 Pa to 105 Pa). Observations have been made with the help of a high speed camera and various characteristics of electric arc under 540 V DC have been studied: the stability arc length, the extinction gap, the arc duration and the mean energy dissipated in the arc. The arc current intensity range is 10–100 A. The obtained results show that the arc stability length, extinction electrode gap, arc duration and energy dissipation in the arc have a direct correlation with the pressure and the current in the circuit.

scholarly journals The Influence of Specimen Geometry and Strain Rate on the Portevin-Le Chatelier Effect and Fracture in an Austenitic FeMnC TWIP Steel

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1201
Author(s):  
Jidong Kang ◽  
Liting Shi ◽  
Jie Liang ◽  
Babak Shalchi-Amirkhiz ◽  
Colin Scott
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Twip Steel ◽  
Image Correlation ◽  
Specimen Geometry ◽  
Dynamic Strain ◽  
Mean Flow ◽  
Chatelier Effect ◽  
The Mean ◽  
Mean Strain

We studied the Portevin-Le Chatelier effect and fracture behavior of a FeMnC TWIP steel using high speed digital image correlation by varying the specimen geometry (flat vs. round) and test strain rate (0.001 vs. 0.1 s−1). The results show that the mean flow stress, the mean strain hardening rate and the mean strain rate sensitivity parameters are all independent of the specimen geometry and are uncorrelated with the presence or not of Portevin-Le Chatelier (PLC) bands, the type of PLC bands observed or the critical strain for band formation. However, both the fracture strains and stresses and the PLC behavior are highly geometry and/or strain rate dependent. Dynamic strain aging (DSA) and in particular the presence of PLC instabilities appears to play an important but as yet unclear role in promoting premature necking and final fracture.

scholarly journals Comparative Analysis of Surface Pressure Fluctuations of High-Speed Train Running in Open-Field and Tunnel Using LES and Wavenumber-Frequency Analysis

2021 ◽  
Vol 11 (24) ◽  
pp. 11702
Author(s):  
Songjune Lee ◽  
Cheolung Cheong ◽  
Byunghee Kim ◽  
Jaehwan Kim
Keyword(s):  
Open Field ◽  
Surface Pressure ◽  
High Speed ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
External Flow ◽  
High Speed Train ◽  
Wall Panel ◽  
Mean Flow ◽  
The Mean

The interior noise of a high-speed train due to the external flow disturbance is more than ever a major problem for product developers to consider during a design state. Since the external surface pressure field induces wall panel vibration of a high-speed train, which in turn generates the interior sound, the first step for low interior noise design is to characterize the surface pressure fluctuations due to external disturbance. In this study, the external flow field of a high-speed train cruising at a speed of 300 km/h in open-field and tunnel are numerically investigated using high-resolution compressible LES (large eddy simulation) techniques, with a focus on characterizing fluctuating surface pressure field according to surrounding conditions of the cruising train, i.e., open-field and tunnel. First, compressible LES schemes with high-resolution grids were employed to accurately predict the exterior flow and acoustic fields around a high-speed train simultaneously. Then, the predicted fluctuating pressure field on the wall panel surface of a train was decomposed into incompressible and compressible ones using the wavenumber-frequency transform, given that the incompressible pressure wave induced by the turbulent eddies within the boundary layer is transported approximately at the mean flow and the compressible pressure wave propagated at the vector sum of the sound speed and the mean flow velocity. Lastly, the power levels due to each pressure field were computed and compared between open-field and tunnel. It was found that there is no significant difference in the power levels of incompressible surface pressure fluctuations between the two cases. However, the decomposed compressible one in the tunnel case is higher by about 2~10 dB than in the open-field case. This result reveals that the increased interior sound of the high-speed train running in a tunnel is due to the compressible surface pressure field.

Turbulent Flow Around Rectangular Cylinders with Different Streamwise Aspect Ratios

2021 ◽  
Author(s):  
Sedem Kumahor ◽  
Mark F. Tachie
Keyword(s):  
Aspect Ratio ◽  
High Speed ◽  
Second Harmonic ◽  
Cylinder Surface ◽  
Large Aspect Ratio ◽  
Reynolds Stresses ◽  
Square Cylinder ◽  
Mean Flow ◽  
Aspect Ratios ◽  
The Mean

Abstract Turbulent flows around a square cylinder and a rectangular cylinder with a streamwise aspect ratio of 5 in a uniform flow were investigated using time-resolved particle image velocimetry. The Reynolds number based on the cylinder height and oncoming flow velocity was 16200. Similarities and differences in the flow dynamics over the cylinders and in the near wake region were examined in terms of the mean flow, Reynolds stresses and triple velocity correlations. The budget of turbulent kinetic energy as well as temporal and spectral analyses were also performed. The results show that the primary, secondary and wake vortexes are smaller for the square cylinder compared to the large aspect ratio cylinder. There are regions of elevated Reynolds stresses and triple velocity correlations along the mean separating streamlines, and the magnitudes of these statistics are an order of magnitude higher over the square cylinder compared to the large aspect ratio cylinder. The topology of the triple velocity correlations shows low-speed ejection and high-speed sweep events, respectively, transporting instantaneous Reynolds normal stresses away from the mean separating streamline into the free-stream and toward the cylinder surface, regardless of aspect ratio. Near the leading and trailing edges of both cylinders, regions of negative turbulence production are observed and the dominant components contributing to this occurrence are discussed. Temporal autocorrelation coefficients of the streamwise and vertical velocity fluctuations show a periodic trend, with a periodicity that is directly linked to the Kármán shedding frequency and its second harmonic.

A Unified Approach for Designing a Radial Flow Gas Turbine

2002 ◽  
Author(s):  
M. S. Y. Ebaid ◽  
F. S. Bhinder ◽  
G. H. Khdairi ◽  
T. S. El-Hasan
Keyword(s):  
Flow Velocity ◽  
Gas Turbine ◽  
High Speed ◽  
Radial Flow ◽  
Electrical Power ◽  
Stream Velocity ◽  
Mean Flow ◽  
Unified Approach ◽  
Aircraft Cabins ◽  
The Mean

Radial flow turbo machines have been used for a long time in a variety of applications such as turbochargers, cryogenics, auxiliary power units, and air conditioning of aircraft cabins. Hence numerous papers have been written on the design and performance of these machines. The only justification for yet another paper is that it would describe a unified approach for designing a single stage inward flow radial turbine comprising a rotor and the casing. The current turbine is designed to drive a direct-coupled permanent magnet high-speed alternator running at 60000 rpm and developing a maximum of 60 kW electrical power. The freedom of choice of the tip diameter and the tip width of the rotor that would be necessary for optimum isentropic efficiency of the turbine stage was restricted by the specified rotational speed and power output. Hence, an optimisation procedure was developed to determine the principal dimension of the rotor. The mean relative velocity in the rotor passages in the direction of the flow would be accelerated but flow velocity on the blade surfaces experiences a significant space rate of deceleration. The rate of deceleration can be controlled by means of a proper choice of the axial length of the rotor. A prescribed mean stream velocity distribution procedure was used to spread the rate of deceleration of the mean flow velocity along the meridional length of the flow passages. The nozzle-less volute casing was designed to satisfy the mass flow rate, energy and angular momentum equations simultaneously. This paper describes the work undertaken to design both the rotor and the casing. The work was motivated by the growing interest in developing gas turbine based hybrid power plant for road vehicles. The authors believe that the paper would lead to a stimulating discussion.

A Unified Approach for Designing a Radial Flow Gas Turbine

2003 ◽  
Vol 125 (3) ◽  
pp. 598-606 ◽  
Author(s):  
M. S. Y. Ebaid ◽  
F. S. Bhinder ◽  
G. H. Khdairi
Keyword(s):  
Flow Velocity ◽  
Gas Turbine ◽  
High Speed ◽  
Radial Flow ◽  
Electrical Power ◽  
Optimization Procedure ◽  
Stream Velocity ◽  
Mean Flow ◽  
Unified Approach ◽  
The Mean

Radial flow turbo machines have been used for a long time in a variety of applications such as turbochargers, cryogenics, auxiliary power units, and air conditioning of aircraft cabins. Hence numerous papers have been written on the design and performance of these machines. The only justification for yet another paper is that it would describe a unified approach for designing a single stage inward flow radial turbine comprising a rotor and the casing. The current turbine is designed to drive a direct-coupled permanent magnet high-speed alternator running at 60000 rpm and developing a maximum of 60 kW electrical power. The freedom of choice of the tip diameter and the tip width of the rotor that would be necessary for optimum isentropic efficiency of the turbine stage was restricted by the specified rotational speed and power output. Hence, an optimization procedure was developed to determine the principal dimension of the rotor. The mean relative velocity in the rotor passages in the direction of the flow would be accelerated but flow velocity on the blade surfaces experiences a significant space rate of deceleration. The rate of deceleration can be controlled by means of a proper choice of the axial length of the rotor. A prescribed mean stream velocity distribution procedure was used to spread the rate of deceleration of the mean flow velocity along the meridional length of the flow passages. The nozzle-less volute casing was designed to satisfy the mass flow rate, energy and angular momentum equations simultaneously. This paper describes the work undertaken to design both the rotor and the casing. The work was motivated by the growing interest in developing gas turbine based hybrid power plant for road vehicles. The authors believe that the paper would lead to a stimulating discussion.

scholarly journals Reliability of the High-speed Camera-based System (HSC-Kinovea) for lower-limb explosive strength endurance assessment in athletes

2020 ◽  
Vol 32 (1) ◽  
Author(s):  
Carlos Gilberto Freitas-Junior ◽  
Pedro Pinheiro Paes ◽  
Leonardo Sousa Fortes ◽  
Alessandro José Da Silva ◽  
Manoel Cunha Costa ◽  
...  
Keyword(s):  
Lower Limb ◽  
High Speed ◽  
Average Power ◽  
High Speed Camera ◽  
Mean Power ◽  
Explosive Strength ◽  
Vertical Jumping ◽  
Jumping Test ◽  
The Mean ◽  
Typical Measurement

The present study verified the reliability of the high-speed camera-based system (HSC-Kinovea) in the lower-limb explosive strength endurance assessment in athletes. Eleven male volleyball players (21.8 ± 2.9 years; 186.3 ± 6.2 cm and 82.3 ± 11.0 kg) participated in the intermittent vertical jumping test in two days. The test was filmed and later analyzed using Kinovea 0.8.15 software to obtain the mean and peak power variables. Regarding reliability, the intra-class correlation coefficient, the typical error of measurements, and Bland-Altman plots were used. The method presented satisfactory values for inter and intra-class correlations (˃ 0.88). The typical values error of measurement presented in the inter-rater analysis was 0.95 W.kg-1 and 0.59 W.kg-1 for the peak and the mean power, respectively. In the intra-assessment analyses, the typical measurement error values were 7.02 W.kg-1 and 5.66 W.kg-1 (test-retest) and 1.59 W.kg-1 and 0.24 W.kg-1  (duplicates videos) for peak and average power, respectively. The HSC-Kinovea system is reliable for assessing the variables of the explosive strength endurance in athletes.

A Study of the Mean and Dynamic Behavior of the Swirling Flow Generated by a Counter Rotating Radial-Radial Swirler Using a Water Test Rig

2015 ◽  
Author(s):  
Wessam Estefanos ◽  
Samir Tambe ◽  
San-Mou Jeng
Keyword(s):  
High Speed ◽  
Swirling Flow ◽  
Flow Instability ◽  
Dominant Frequency ◽  
Flow Dynamics ◽  
Test Rig ◽  
Water Testing ◽  
Water Test ◽  
The Mean ◽  
Unsteady Behavior

An experimental investigation has been conducted to study the mean and unsteady behavior of the non-reacting swirling flow using a water test rig. Water was used as the flow medium as for a given Reynolds number (Re), the flow dynamics are slowed down by about 18 times compared to atmospheric air making it easier to investigate the flow dynamics. The flow was examined using a 3X model of a counter rotating radial-radial swirler. 2D high speed Particle Image Velocimetry (PIV) measurements were employed to study the instantaneous and the mean velocity fields. Tests were conducted at Re values corresponding to an air pressure drop of 4%, 2.8%, 1.8% and 1% of atmospheric pressure for the corresponding 1X model of the swirler under atmospheric test conditions. The use of water to test the unsteady behavior of the swirling flow was validated by conducting tests on the same 3X model in the same test rig using air at the same Re values. The mean and turbulent behavior of the swirling flow in water and air showed excellent agreement over the range of Re tested. For this swirler, the normalized mean and RMS velocities did not change significantly with Re for the range of Re tested. Strong flow instability was observed at the exit of the swirler. This instability was created by a precessing vortex core (PVC). For air and water tests, the dominant frequency of this instability increased linearly with the increase in Re. For all Re investigated, the dominant frequency of water flow was 18 times less than that of air at the same Re. The Strouhal number was found to be nearly identical for air and water testing for all Re values. Maximum Turbulent Kinetic Energy (TKE) was found to exist on the boundaries of strong shear layers. The TKE decayed quickly downstream due to the quick decay of the PVC. The phase angle difference between the high TKE regions was 3.14 radians indicating a circumferential mode of instability. The results obtained demonstrate that water testing is an accepted method for studying the unsteady flows.

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