Spatiotemporally-Resolved Dynamics of Dispersing Ferrofluid Aggregates

2008 ◽  
Author(s):  
Alicia M. Williams ◽  
Pavlos P. Vlachos
Keyword(s):  
Internal Flow ◽  
Bulk Flow ◽  
Experimental Techniques ◽  
Recirculation Region ◽  
Complex Flow ◽  
Time Resolved ◽  
Square Channel ◽  
Spatiotemporal Behavior ◽  
Pulsatile Flows ◽  
The Impact

Ferrohydrodynamics research has been approached predominantly from either numerical or basic experimental techniques. However, to date, these experimental techniques have been limited to ultrasonic point measurements or shadowgraphs due to the opacity of the ferrofluids. As a result, the complete dynamics of many ferrohydrodynamics flows have remained unexplored. In this work, Time Resolved Digital Particle Image Velocimetry (TRDPIV) is employed to fully resolve the dynamic interaction of ferrofluid aggregates with bulk nonmagnetic fluids. This topic is hydrodynamically rich, where shearing between the aggregate and bulk flow develop into the Kelvin-Helmholtz instability. Ferrofluid aggregates are mixed with fluorescent particles in order to enable visualization of the internal flow structure of the aggregate and generate quantitative velocity measurements. The TRDPIV measurements are made in a 15 mm square channel where ferrofluid retained by a 0.5 Tesla permanent magnet is studied as it disperses. The effects of both steady and pulsatile flows are quantified, as are the impact of varying the magnetic field gradients. In both steady and pulsatile flows, a recirculation region is observed within the ferrofluid, driven by the shear layer between the bulk flow and aggregate interface. The interaction of the aggregate with the flow is also governed by the aggregate height relative to that of the test section. Higher, larger aggregates are less stable, and therefore, more likely to be dispersed by the bulk flow. As the aggregate diminishes in size, it is both more stable and is less subject to shearing forces from the flow. Flow pulsatility enriches the dynamics of the flow and generates complex flow structures resulting from interaction between the aggregate and bulk flow. This work is the first to explore the rich spatiotemporal behavior of dispersing ferrofluid aggregates interacting with steady and unsteady bulk flows.

Developing and Fully Developed Turbulent Flow in Ribbed Channels

2008 ◽  
Author(s):  
N. D. Cardwell ◽  
P. P. Vlachos ◽  
K. A. Thole
Keyword(s):  
Large Scale ◽  
Internal Flow ◽  
Field Measurements ◽  
Homogeneous Distribution ◽  
Channel Height ◽  
Time Resolved ◽  
Number Range ◽  
Cooling Channels ◽  
Square Channel ◽  
Fully Developed Turbulent Flow

Modern turbomachines operate at combustion temperatures well beyond the incipient melting point of the turbine’s metal components. Cooling channels within turbine airfoils directly affect component lifecycle in addition to influencing almost all aspects of the overall engine design. However, many aspects regarding flow structure and vortex dynamics within these cooling channels are still unknown. In this study, high fidelity Time Resolved Digital Particle Image Velocimetry (TRDPIV) was used to investigate a ribbed cooling channel. The design consisted of a square channel having square transverse ribs which were staggered on both the top and bottom walls. Rib spacing was matched to the channel height and the rib to channel height ratio was kept constant at 0.13. The Reynolds number range investigated was between 2,500 and 20,000. Flow field measurements were performed at the entrance to and within the developed rib roughened section, corresponding to the 1st and 12th ribs. Overall, the results indicate that large scale coherent vortical structures were generated by the presence of the front rib surface and enclosed wake region between the ribs. Higher values of vortex circulation strength were observed for Re = 2,500 in addition to a more homogeneous distribution of identified coherent structures at the developed section. In addition to providing insight and feedback for a common turbine cooling design, this study also illuminates the vortex distribution for a highly turbulent and complex internal flow.

Flow features resulting from shock wave impact on a cylindrical cavity

2007 ◽  
Vol 580 ◽  
pp. 481-493 ◽  
Author(s):  
BERIC W. SKEWS ◽  
HARALD KLEINE
Keyword(s):  
Shock Wave ◽  
High Speed ◽  
Shear Layers ◽  
Complex Flow ◽  
Wave Impact ◽  
Time Resolved ◽  
Additional Information ◽  
Flow Features ◽  
Time Resolved Imaging ◽  
The Impact

The complex flow features that arise from the impact of a shock wave on a concave cavity are determined by means of high-speed video photography. Besides additional information on features that have previously been encountered in specific studies, such as those relating to shock wave reflection from a cylindrical wall and those associated with shock wave focusing, a number of new features become apparent when the interaction is studied over longer times using time-resolved imaging. The most notable of these new features occurs when two strong shear layers meet that have been generated earlier in the motion. Two jets can be formed, one facing forward and the other backward, with the first one folding back on itself. The shear layers themselves develop a Kelvin–Helmholtz instability which can be triggered by interaction with weak shear layers developed earlier in the motion. Movies are available with the online version of the paper.

Effect of Buoyancy and Density Ratio on Heat Transfer in a Smooth Cooling Channel of a Gas Turbine Blade

2018 ◽  
Author(s):  
Mandana S. Saravani ◽  
Saman Beyhaghi ◽  
Ryoichi S. Amano
Keyword(s):  
Heat Transfer ◽  
Rotational Speed ◽  
Cfd Simulation ◽  
Density Ratio ◽  
Reynolds Numbers ◽  
Buoyancy Effect ◽  
Square Channel ◽  
First Case ◽  
Computational Fluid Dynamics Cfd ◽  
The Impact

The present work investigates the effects of buoyancy and density ratio on the thermal performance of a rotating two-pass square channel. The U-bend configuration with smooth walls is selected for this study. The channel has a square cross-section with a hydraulic diameter of 5.08 cm (2 inches). The lengths of the first and second passes are 514 mm and 460 mm, respectively. The turbulent flow enters the channel with Reynolds numbers of up to 34,000. The rotational speed varies from 0 to 600 rpm with the rotational numbers up to 0.75. For this study, two approaches are considered for tracking the buoyancy effect on heat transfer. In the first case, the density ratio is set constant, and the rotational speed is varied. In the second case, the density ratio is changed in the stationary case, and the effect of density ratio is discussed. The range of Buoyancy number along the channel is 0–6. The objective is to investigate the impact of Buoyancy forces on a broader range of rotation number (0–0.75) and Buoyancy number scales (0–6), and their combined effects on heat transfer coefficient for a channel with aspect ratio of 1:1. Several computational fluid dynamics (CFD) simulation are carried out for this study, and some of the results are validated against experimental data.

Surface Roughness Impact on Secondary Flow and Losses in a Turbine Exhaust Casing

2018 ◽  
Author(s):  
Isak Jonsson ◽  
Valery Chernoray ◽  
Borja Rojo
Keyword(s):  
Surface Roughness ◽  
Secondary Flow ◽  
Suction Side ◽  
Pressure Probe ◽  
Time Resolved ◽  
Pressure Distributions ◽  
Turbulence Decay ◽  
Inlet Swirl ◽  
High Level ◽  
The Impact

This paper experimentally addresses the impact of surface roughness on losses and secondary flow in a Turbine Rear Structure (TRS). Experiments were performed in the Chalmers LPT-OGV facility, at an engine representative Reynolds number with a realistic shrouded rotating low-pressure turbine (LPT). Outlet Guide Vanes (OGV) were manufactured to achieve three different surface roughnesses tested at two Reynolds numbers, Re = 235000 and Re = 465000. The experiments were performed at on-design inlet swirl conditions. The inlet and outlet flow of the TRS were measured in 2D planes with a 5-hole probe and 7-hole probe accordingly. The static pressure distributions on the OGVs were measured and boundary layer studies were performed at the OGV midspan on the suction side with a time-resolved total pressure probe. Turbulence decay was measured within the TRS with a single hot-wire. The results showed a surprisingly significant increase in the losses for the high level of surface roughness (25–30 Ra) of the OGVs and Re = 465000. The increased losses were primary revealed as a result of the flow separation on the OGV suction side near the hub. The loss increase was seen but was less substantial for the intermediate roughness case (4–8 Ra). Experimental results presented in this work provide support for the further development of more advanced TRS and data for the validation of new CFD prediction methods for TRS.

Numerical solutions to wave interaction with rubblemound breakwaters

1990 ◽  
Vol 17 (2) ◽  
pp. 252-261 ◽  
Author(s):  
Kevin R. Hall
Keyword(s):  
Numerical Modelling ◽  
Numerical Solution ◽  
Numerical Solutions ◽  
Scale Effects ◽  
Numerical Models ◽  
Internal Flow ◽  
Wave Interaction ◽  
Theoretical Development ◽  
Porous Media Flow ◽  
Complex Flow

The interaction of a wave with a rubblemound breakwater results in a complex flow field which is both nonlinear and turbulent, particularly within a region close to the surface of the structure. Numerical models describing internal flow in a rubblemound breakwater are becoming increasingly important, particularly as the influence of scale effects on internal flow in physical hydraulic models are becoming understood as important. A number of numerical models to predict the internal breakwater flow kinematics have been produced in the past two decades. This paper provides a review of the state-of-the-art of numerical modelling of wave interaction with rubblemound breakwaters. Details of the theoretical development and the resulting numerical solution techniques are presented. Methods for incorporating secondary effects such as two-phase (air–water) flow, inertia, and unbalanced boundary conditions are discussed. Limitations of the models resulting from the validity of the assumptions made in order to effect a numerical solution are discussed. Key words: breakwaters, internal flow, porous media flow, numerical modelling, rubblemound breakwaters.

Effect of Rotor-Stator Configuration in the Generation of Vortical Scales and Wake Mixing in Single Stage Axial Fans: Part II — Assessment of Vortex Sound Sources

2013 ◽  
Author(s):  
Mónica Galdo Vega ◽  
Jesus Manuel Fernandez Oro ◽  
Katia María Argüelles Díaz ◽  
Carlos Santolaria Morros
Keyword(s):  
Deep Understanding ◽  
Operating Conditions ◽  
Axial Fan ◽  
Noise Sources ◽  
Sound Sources ◽  
Time Resolved ◽  
Vortex Sound ◽  
Starting Point ◽  
Axial Fans ◽  
The Impact

This second part is devoted to the identification of vortex sound sources in low-speed turbomachinery. As a starting point, the time-resolved evolution of the vortical motions associated to the wake shear layers (reported in the first part of the present study) is employed to obtain vorticity distributions in both blade-to-blade and traverse locations throughout the axial fan stage. Following, the Powell analogy for generation of vortex sound is revisited to obtain the noise sources in the nearfield region of the fan. Both numerical and experimental databases presented previously are now post-processed to achieve a deep understanding of the aeroacoustic behavior of the vortical scales present in the flow. A LES simulation at midspan, using a 2.5D scheme, allows an accurate description of the turn-out time of the shedding vortices, within high-density meshes in the blades and vanes passages, and a correct modeling of the dynamics of turbulence. Besides, thermal anemometry has been employed with a two-wire probe to measure the planar flow in the midspan sections of the fan. Statistical procedures and signal conditioning of velocity traces have confirmed experimentally the unsteady flow patterns devised in the numerical model. The comparison of the rotor-stator and the stator-rotor configurations provides the influence of the wake mixing and the nucleation of turbulent spots in the distribution of the Powell source terms. Moreover, the relation between the turbomachine configuration and the generation of vortex sound can be established, including the impact of the operating conditions and the contributions of the interaction mechanisms.

Assessment of the impact of oxidation processes on indoor air pollution using the new time-resolved INCA-Indoor model

2015 ◽  
Vol 122 ◽  
pp. 521-530 ◽  
Author(s):  
Maxence Mendez ◽  
Nadège Blond ◽  
Patrice Blondeau ◽  
Coralie Schoemaecker ◽  
Didier A. Hauglustaine
Keyword(s):  
Air Pollution ◽  
Indoor Air ◽  
Indoor Air Pollution ◽  
Time Resolved ◽  
Oxidation Processes ◽  
The Impact ◽  
New Time

scholarly journals Computational Analysis on Numerical Simulation of Internal Flow Physics for Pump as Turbine in Renewable Small Hydro Energy Generation

Complexity ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Du Jianguo ◽  
Daniel Adu ◽  
Emmanuel Acheaw ◽  
Shakir Hafeez ◽  
Eric Ofosu Antw
Keyword(s):  
Flow Rate ◽  
Rotational Speed ◽  
Human Life ◽  
Three Dimensional ◽  
Internal Flow ◽  
Hydroelectric Power ◽  
Small Hydropower ◽  
Speed Increase ◽  
Blade Thickness ◽  
The Impact

Energy contributes significantly in almost all aspects of human life as well as economic activities and plays a crucial role in the infrastructural development of a county to alleviate poverty. Generating energy from a renewable source such as small hydropower through the application of pump operating as a turbine mode called Pump as Turbine is one of the best alternatives to provide clean and inexpensive energy. Using Pump as Turbine helps in generating reasonably priced hydroelectric power for communities in underdeveloped counties. This study investigates the effects of internal flow behaviour and performance of Pump as Turbine under different rotational speed and flow rate. The rotational speed is an essential physical parameter as it affects the Pump as Turbine operation. A model-specific speed centrifugal pump model with head 32 (m), flow rate of 12.5 (m3/h) and the rotational speed of 2900 rpm, has been selected for the study. Numerical simulations have been conducted using the k-ω turbulence model to solve three-dimensional (3D) equations. The pump mode experimental data were used to confirm the results for better analysis. The results predicted that vortex and turbulent kinetic energy increase per rotational speed increase. Also, at the higher rotational speed, very high recirculation of flow is detected at the blade suction chamber, although the pressure side has a smooth flow. This study provides beneficial information which will serve as a reference to help improve PAT performance along with selecting PAT for a small hydropower site. Future works will consider the impact of blade thickness and cavitation in Pump as Turbine.

The Impact of Volute Versus Collector on Centrifugal Compressor Performance

2002 ◽  
Author(s):  
Y. I. Biba
Keyword(s):  
3D Model ◽  
Internal Flow ◽  
Performance Measurements ◽  
Cross Sectional ◽  
Flow Rates ◽  
Computational Fluid Dynamics Cfd ◽  
Compressor Performance ◽  
The Subject ◽  
Cfd Analyses ◽  
The Impact

As part of a revamp or rerate study, an investigation was undertaken to assess the impact of a collector design versus a volute on compressor performance. The subject compressor was a single stage, axial inlet configuration with a discharge collector rather than the more commonly used scroll volute. The primary distinction between the collector and volute is that the collector cross sectional area is constant at all circumferential locations. A complex 3D model containing the inlet, impeller, low solidity diffuser (LSD), and collector was built. A similar model was also created where the volute was substituted for the collector. Computational Fluid Dynamics (CFD) analyses were performed using these models with results generated at different flow rates. Computational results are presented and compared to test data for collector configuration. The test included standard performance measurements as well as more detailed internal flow data, allowing a credible comparison with the CFD results. Conclusions are drawn with respect to potential compromises in choosing a collector versus a volute.

Study on Influence of Nozzle Structure on Flow in Diesel Nozzle Orifice

2012 ◽  
Vol 246-247 ◽  
pp. 127-130
Author(s):  
Bing Li ◽  
Xue Song Hu ◽  
Xiao Feng Cao ◽  
Gui Qi Jia ◽  
Fang Xi Xie ◽  
...  
Keyword(s):  
Flow Characteristics ◽  
Internal Flow ◽  
Key Factors ◽  
Complex Flow ◽  
Two Phase ◽  
Nozzle Orifice ◽  
Fuel Flow ◽  
Flow Features ◽  
Diesel Nozzle ◽  
Nozzle Hole

The fuel flow characteristics in diesel nozzle orifice are key factors to the atomization of fuel near the nozzle orifice. In the paper, two-phase flow model is used to simulate the complex flow features in nozzle orifice, and to study the influences of the relative position of nozzles orifice axis and nozzle axis, and inclination angle of nozzle hole on the internal flow feature.

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