Characteristics of Glottis-Induced Turbulence in Oscillatory Flow: An Empirical Investigation

1998 ◽  
Vol 120 (2) ◽  
pp. 217-226 ◽  
Author(s):  
Yongchul Choi ◽  
D. E. Wroblewski
Keyword(s):  
Oscillatory Flow ◽  
Shear Stresses ◽  
Circular Aperture ◽  
Flow Conditions ◽  
Velocity Measurements ◽  
Acceleration Phase ◽  
Component Velocity ◽  
High Turbulence ◽  
Decaying Turbulence

Turbulence inducement from the glottis was scrutinized by employing an idealized model of the larynx and trachea for oscillatory flow conditions. The characterization of turbulence was achieved with the two-component velocity measurements of split-film probe anemometry and with the flow visualization of a smoke-wire technique. The apertures of two different (triangular and circular) shapes were utilized in the airway model to address the distinct effects of the triangular-shaped glottal aperture on the generation, development, and decay of turbulence. One of the salient turbulence characteristics for the triangular aperture case was found to be the relatively high turbulence levels around the center region (2r/D ~ 0) in conjunction with the asymmetric mean axial velocity across the frontal-rear (A-O-P) plane of the trachea at one tracheal diameter (x/D = 1) downstream from the glottis. The detailed turbulence properties such as the Reynolds shear stresses and turbulence intensities for the triangular aperture case differed significantly from those for the circular aperture case within a few tracheal diameters (x/D < 7) downstream from the apertures. The glottis-induced turbulence was incipient during the acceleration phase of inspiration and convected downstream with the traits of decaying turbulence.

scholarly journals Experimental Characterization of the Flow Field around Oblong Bridge Piers

Fluids ◽  
2021 ◽  
Vol 6 (11) ◽  
pp. 370
Author(s):  
Ana Margarida Bento ◽  
Teresa Viseu ◽  
João Pedro Pêgo ◽  
Lúcia Couto
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Bridge Pier ◽  
Bridge Piers ◽  
Shear Stresses ◽  
Velocity Measurements ◽  
Bridge Foundations ◽  
Scour Hole ◽  
Movable Bed

The prediction of scour evolution at bridge foundations is of utmost importance for engineering design and infrastructures’ safety. The complexity of the scouring inherent flow field is the result of separation and generation of multiple vortices and further magnified due to the dynamic interaction between the flow and the movable bed throughout the development of a scour hole. In experimental environments, the current approaches for scour characterization rely mainly on measurements of the evolution of movable beds rather than on flow field characterization. This paper investigates the turbulent flow field around oblong bridge pier models in a well-controlled laboratory environment, for understanding the mechanisms of flow responsible for current-induced scour. This study was based on an experimental campaign planned for velocity measurements of the flow around oblong bridge pier models, of different widths, carried out in a large-scale tilting flume. Measurements of stream-wise, cross-wise and vertical velocity distributions, as well as of the Reynolds shear stresses, were performed at both the flat and eroded bed stages of scouring development with a high-resolution acoustic velocimeter. The time-averaged values of velocity and shear stress are larger in the presence of a developed scour hole than in the corresponding flat bed configuration.

Three component velocity measurements of an isothermal confined swirling flow

1997 ◽  
Vol 211 (2) ◽  
pp. 113-122 ◽  
Author(s):  
S A Ahmed
Keyword(s):  
Swirling Flow ◽  
Sudden Expansion ◽  
Recirculation Region ◽  
Laser Doppler Velocimeter ◽  
Velocity Measurements ◽  
Radial Velocity Component ◽  
Numerical Predictions ◽  
Velocity Gradients ◽  
Component Velocity ◽  
High Turbulence

A two-component fibre-optic laser Doppler velocimeter (LDV) system has been employed to measure the flowfield characteristics of a confined, isothermal strongly swirling flow in a combustor model. The primary objectives are to understand such complex flowfields and to provide complete benchmark data for comparisons with numerical predictions based on practical models for turbulent swirling flows, and thereby guide the development of such models. For this confined strongly swirling flow, the measurements show the radial velocity component (close to the swirler exit) to be of the same order as the axial and swirl components. Comprehensive and detailed data show a large central recirculation region close to the dump plane which extends beyond the last measurement station. High velocity gradients and high turbulence activities are common for this type of flow and the current set of data confirms these previous findings. Generally speaking, most of the mixing takes place in the shear layer between the annular swirling jet and the corner recirculation region due to the sudden expansion.

Evaluation of Different Turbulence Models for the Characterization of Shear Stresses in the Central Venous Access for Hemodialysis

2020 ◽  
Author(s):  
Saulo Gonçalves ◽  
Matheus Costa ◽  
Thabata Lucas ◽  
Jonathas Haniel ◽  
Mário Silva ◽  
...  
Keyword(s):  
Central Venous Access ◽  
Turbulence Models ◽  
Venous Access ◽  
Shear Stresses ◽  
Central Venous

Modeling of mass transfer in biofilms in oscillatory flow conditions using k-ɛ turbulence model

2003 ◽  
Vol 3 (1-2) ◽  
pp. 201-207
Author(s):  
H. Nagaoka ◽  
T. Nakano ◽  
D. Akimoto
Keyword(s):  
Numerical Simulation ◽  
Mass Transfer ◽  
Turbulence Model ◽  
Uptake Rate ◽  
Oscillatory Flow ◽  
Substrate Uptake ◽  
Flow Conditions ◽  
Mass Transfer Mechanism ◽  
Substrate Uptake Rate ◽  
Good Agreement

The objective of this research is to investigate mass transfer mechanism in biofilms under oscillatory flow conditions. Numerical simulation of turbulence near a biofilm was conducted using the low Reynold’s number k-ɛ turbulence model. Substrate transfer in biofilms under oscillatory flow conditions was assumed to be carried out by turbulent diffusion caused by fluid movement and substrate concentration profile in biofilm was calculated. An experiment was carried out to measure velocity profile near a biofilm under oscillatory flow conditions and the influence of the turbulence on substrate uptake rate by the biofilm was also measured. Measured turbulence was in good agreement with the calculated one and the influence of the turbulence on the substrate uptake rate was well explained by the simulation.

Point-of-Care Diagnostic Assays and Novel Preclinical Technologies for Hemostasis and Thrombosis

2021 ◽  
Vol 47 (02) ◽  
pp. 120-128
Author(s):  
Christina Caruso ◽  
Wilbur A. Lam
Keyword(s):  
Point Of Care ◽  
Healing Process ◽  
Coagulation Factors ◽  
Wound Healing Process ◽  
Shear Stresses ◽  
Flow Conditions ◽  
Novel Technologies ◽  
Clinical Consequences ◽  
Complex Wound ◽  
Reproducible Analysis

AbstractHemostasis is a complex wound-healing process involving numerous mechanical and biochemical mechanisms and influenced by many factors including platelets, coagulation factors, and endothelial components. Slight alterations in these mechanisms can lead to either prothrombotic or bleeding consequences, and such hemostatic imbalances can lead to significant clinical consequences with resultant morbidity and mortality. An ideal hemostasis assay would not only address all the unique processes involved in clot formation and resolution but also take place under flow conditions to account for endothelial involvement. Global assays do exist; however, these assays are not flow based. Flow-based assays have been limited secondary to their large blood volume requirements and low throughput, limiting potential clinical applications. Microfluidic-based assays address the aforementioned limitations of both global and flow-based assays by utilizing standardized devices that require low blood volumes, offer reproducible analysis, and have functionality under a range of shear stresses and flow conditions. While still largely confined to the preclinical space, here we aim to discuss these novel technologies and potential clinical implications, particularly in comparison to the current, commercially available point-of-care assays.

scholarly journals Optimization of the flow conditions in the spawning ground of the Chinese sturgeon (Acipenser sinensis) through Gezhouba Dam generating units

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Anyang Huang ◽  
Jinzhong Yao ◽  
Jiazhi Zhu ◽  
Xingchen Gao ◽  
Wei Jiang
Keyword(s):  
Spawning Ground ◽  
Chinese Sturgeon ◽  
Flow Conditions ◽  
Velocity Measurements ◽  
Acipenser Sinensis ◽  
Critically Endangered Species ◽  
Gezhouba Dam ◽  
Opening Mode ◽  
Suitable Area ◽  
Good Agreement

AbstractChinese sturgeon (Acipenser sinensis) is a critically endangered species, and waters downstream from Gezhouba Dam are the only known spawning ground. To optimize the velocity conditions in the spawning ground by controlling the opening mode of Gezhouba Dam generator units, a mathematical model of Chinese sturgeon spawning ground was established in FLOW-3D. The model was evaluated with velocity measurements, and the results were determined to be in good agreement. By inverting the 2016–2019 field monitoring results, the model shows that the preferred velocity range for Chinese sturgeon spawning is 0.6–1.5 m/s. Velocity fields of different opening modes of the generator units were simulated with identical discharge. The suitable-velocity area was maximal when all units of Dajiang Plant of Gezhouba Dam were open. For discharges below 12,000 m3/s, most of the area was suitable; for discharges above 12,000 m3/s, the suitable area rapidly decreased with increasing discharge. A comparison of suitable areas under high-flow showed that at discharges of 12,000–15,000 m3/s, opening 11–13 units on the left side was optimal. For discharges above 15,000 m3/s, all units should be open. We used these results to recommend a new operation scheme to support the conservation of Chinese sturgeon.

Measurements of real non-Newtonian response for liquid lubricants under moderate pressures

2001 ◽  
Vol 215 (3) ◽  
pp. 223-233 ◽  
Author(s):  
S Bair
Keyword(s):  
Numerical Simulation ◽  
Kinetic Theory ◽  
Simple Shear ◽  
Pressure Dependence ◽  
Shear Stresses ◽  
Current Interest ◽  
Flow Properties ◽  
Power Law Fluid ◽  
Temperature And Pressure

A thorough characterization of all viscous flow properties relevant to steady simple shear was carried out for five liquid lubricants of current interest to tribology. Shear stresses were generated to values significant to concentrated contact lubrication. Two types of non-Newtonian response were observed: shear-thinning as a power-law fluid and near rate-independence. Functions and parameters were obtained for the temperature and pressure dependence of the viscosity and of the time constant for the Carreau-Yasuda equation. Results are consistent with free volume and kinetic theory, but directly contradict many assumptions currently utilized for numerical simulation and for extracting rheological properties from contact measurements.

Velocity measurements close to the bed in a wave tank

1970 ◽  
Vol 42 (1) ◽  
pp. 111-123 ◽  
Author(s):  
J. F. A. Sleath
Keyword(s):  
Velocity Distribution ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
Velocity Measurements ◽  
Dominant Effect ◽  
Wave Tank ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Laminar Flow Conditions

Measurements of the velocity distribution close to the bed have been made under laminar flow conditions in a wave tank. The classical solution for the velocity distribution was found to be valid when the bed was smooth, but considerable deviations between theory and experiment were observed with beds of sand. It is suggested that these deviations were caused by vortex formation around the grains of sand. The similarity between the velocity profiles obtained in these tests and those reported by other writers under supposedly turbulent conditions suggests that even at high Reynolds numbers vortex formation may continue to be the dominant effect in oscillatory boundary layers of this sort.

Effusion-Cooling Performance at Gas Turbine Combustor Representative Flow Conditions

2012 ◽  
Author(s):  
Vinod U. Kakade ◽  
Steven J. Thorpe ◽  
Miklós Gerendás
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Free Stream ◽  
Flow Conditions ◽  
Cooling Performance ◽  
Free Stream Turbulence ◽  
High Turbulence ◽  
Adiabatic Effectiveness

The thermal management of aero gas turbine engine combustion systems commonly employs effusion-cooling in combination with various cold-side convective cooling schemes. The combustor liner incorporates many small holes which are usually set in staggered arrays and at a shallow angle to the cooled surface; relatively cold compressor delivery air is then allowed to flow through these holes to provide the full-coverage film-cooling effect. The efficient design of such systems requires robust correlations of film-cooling effectiveness and heat transfer coefficient at a range of aero-thermal conditions, and the use of appropriately validated computational models. However, the flow conditions within a combustor are characterised by particularly high turbulence levels and relatively large length scales. The experimental evidence for performance of effusion-cooling under such flow conditions is currently sparse. The work reported here is aimed at quantifying typical effusion-cooling performance at a range of combustor relevant free-stream conditions (high turbulence), and also to assess the importance of modeling the coolant to free-stream density ratio. Details of a new laboratory wind-tunnel facility for the investigation of film-cooling at high turbulence levels are reported. For a typical combustor effusion geometry that uses cylindrical holes, spatially resolved measurements of adiabatic effectiveness, heat transfer coefficient and net heat flux reduction are presented for a range of blowing ratios (0.48 to 2), free-stream turbulence conditions (4 and 22%) and density ratios (0.97 and 1.47). The measurements reveal that elevated free-stream turbulence impacts on both the adiabatic effectiveness and heat transfer coefficient, although this is dependent upon the blowing ratio being employed and particularly the extent to which the coolant jets detach from the surface. At low blowing ratios the presence of high turbulence levels causes increased lateral spreading of the coolant adjacent to the injection points, but more rapid degradation in the downstream direction. At high blowing ratios, high turbulence levels cause a modest increase in effectiveness due to turbulent transport of the detached coolant fluid. Additionally, the augmentation of heat transfer coefficient caused by the coolant injection is seen to be increased at high free-stream turbulence levels.

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