scholarly journals A conveyor belt experimental setup to study the internal dynamics of granular avalanches

2021 ◽  
Vol 62 (10) ◽  
Author(s):  
Tomás Trewhela ◽  
Christophe Ancey
Keyword(s):  
Leading Edge ◽  
Wave Structure ◽  
Velocity Slip ◽  
Coarse Graining ◽  
Conveyor Belt ◽  
Experimental Setup ◽  
Size Segregation ◽  
Coupled Models ◽  
Refractive Index Matching ◽  
Velocity Changes

Abstract This paper shows how a conveyor belt setup can be used to study the dynamics of stationary granular flows. To visualise the flow within the granular bulk and, in particular, determine its composition and the velocity field, we used the refractive index matching (RIM) technique combined with particle tracking velocimetry and coarse-graining algorithms. Implementing RIM posed varied technical, design and construction difficulties. To test the experimental setup and go beyond a mere proof of concept, we carried out granular flow experiments involving monodisperse and bidisperse borosilicate glass beads. These flows resulted in stationary avalanches with distinct regions whose structures were classified as: (i) a convective-bulged front, (ii) a compact-layered tail and, between them, (iii) a breaking size-segregation wave structure. We found that the bulk strain rate, represented by its tensor invariants, varied significantly between the identified flow structures, and their values supported the observed avalanche characteristics. The flow velocity fields’ interpolated profiles adjusted well to a Bagnold-like profile, although a considerable basal velocity slip was measured. We calculated a segregation flux using recent developments in particle-size segregation theory. Along with vertical velocity changes and high expansion rates, segregation fluxes were markedly higher at the avalanche’s leading edge, suggesting a connection between flow rheology and grain segregation. The experimental conveyor belt’s results showed the potential for further theoretical developments in rheology and segregation-coupled models. Graphic Abstract

Internal dynamics of steady and nearly uniform granular avalanches

2021 ◽  
Author(s):  
Tomas Trewhela ◽  
Christophe Ancey
Keyword(s):  
Wave Structure ◽  
Coarse Graining ◽  
Local Strain ◽  
Conveyor Belt ◽  
Size Segregation ◽  
Internal Dynamics ◽  
Particle Distributions ◽  
Index Matching ◽  
Recent Developments ◽  
Refractive Index Matching

<p><span>We experimentally investigated the internal dynamics of stationary mono- and bidisperse granular avalanches in an inclined conveyor belt flume. We used the refractive index matching technique to visualize and obtain information from within the granular bulk. In combination with particle tracking velocimetry and coarse-graining techniques, we were able to calculate continuum particle distributions and velocity fields. The experimental avalanches had distinct flow regions: (i) a convective-bulged front, (ii) a compact-layered tail, and (iii) a breaking size segregation wave structure, serving as a transition between the former two. To describe the dynamics of these regions, we computed local strain rates in the form of its tensor invariants. The invariants varied notably between regions; while the largest values and non-linear distributions were found at the front, linear distributions were observed in the tail. In general, and although that slip was considerable at the base of the flow, time-averaged velocity profiles were found to be well captured by a Bagnold model. Based on recent developments in particle-size segregation theory, we calculated the segregation flux within the bidisperse avalanches. In those experiments, we found that segregation flux was higher at the front than at the back, a fact that was confirmed by the observed recirculation of large particles at the front. All our experimental data show a strong link between rheology and segregation, a result that will provide grounding for new developments in segregation theory.</span></p>

scholarly journals Aeroacoustic Optimization of the Bionic Leading Edge of a Typical Blade for Performance Improvement

Machines ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 175
Author(s):  
Haoran Liu ◽  
Yeming Lu ◽  
Jinguang Yang ◽  
Xiaofang Wang ◽  
Jinjun Ju ◽  
...  
Keyword(s):  
Performance Improvement ◽  
Sound Pressure ◽  
Leading Edge ◽  
Wave Structure ◽  
Mechanism Analysis ◽  
Optimization Strategy ◽  
Flow Mechanism ◽  
Adjustment Factor ◽  
Bionic Blade ◽  
The Mean

New, innovative optimization approaches to improve turbomachine performance and reduce turbomachine noise are significant in engineering. In this paper, based on the bionic concept, a wave structure is used to shape the leading edge of the blade. Using an NACA0018 blade as the basic blade, a united parametric approach controlled by three parameters is proposed to configure the wavy leading edge. Then, a new optimization strategy boosting design efficiency is established to output the optimal design results. Finally, the corresponding performance and flow mechanism are analyzed. Taking into account the existence of the hub wall and the shroud wall from the closed impeller, a near-wall adjustment factor is added, the significance of which is herein demonstrated. An optimal bionic blade is successfully obtained by the optimization strategy, which can reduce the mean drag coefficient by about 6% and the overall sound pressure level by about 3 dB, in relative to the original blade. Mechanism analysis revealed that the wave structure can induce spanwise velocity at the leading edge and cause a further delay in flow separation in the downstream region, synchronously reducing drag and noise.

Numerical study of velocity slip of phases during the passage of a shock wave of low intensity from a pure gas to a dusty medium

2019 ◽  
Vol 14 (2) ◽  
pp. 125-131 ◽  
Author(s):  
D.A. Tukmakov
Keyword(s):  
Shock Wave ◽  
Particle Size ◽  
Numerical Study ◽  
Leading Edge ◽  
Velocity Slip ◽  
Fold Increase ◽  
Dispersed Phase ◽  
Grid Function ◽  
Dynamic Force ◽  
Dispersed Phases

In this paper, the process of the movement of a direct shock wave from a pure gas into a dusty medium is numerically modeled. The mathematical model took into account the viscosity, compressibility and thermal conductivity of the carrier phase. Also, the modeling technique made it possible to describe the interphase force interaction, which included the Stokes force, the dynamic force of Archimedes, the strength of the attached masses. In addition, interfacial interaction included heat transfer between the carrier and dispersed phases. The numerical solution was carried out using the explicit finite-difference method, with the subsequent application of the nonlinear correction scheme for the grid function. As a result of numerical calculations, it was revealed that with an increase in the linear particle size of the gas suspension, the velocity slip between the carrier and dispersed phases increases. Numerical modeling also showed that the absolute value of the difference between the velocities of the carrier and the dispersed phase reaches the largest value at the leading edge of the compression wave. The revealed regularities can be explained by the fact that the particles of the dispersed phase are assumed to be spherical in shape. Due to this, a multiple increase in particle size leads to a three-fold increase in their mass, a twofold increase in the area of one particle and a three-fold decrease in the number of particles. Thus, an increase in particle size leads to a decrease in the area of interfacial contact and an increase in the inertia of the particles, which in turn affects the interfacial velocity slip.

scholarly journals Wake Effect Assessment in Long- and Short-Crested Seas of Heaving-Point Absorber and Oscillating Wave Surge WEC Arrays

Water ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 1126 ◽  
Author(s):  
Gael Verao Fernandez ◽  
Vasiliki Stratigaki ◽  
Panagiotis Vasarmidis ◽  
Philip Balitsky ◽  
Peter Troch
Keyword(s):  
Wave Propagation ◽  
Wave Structure ◽  
Irregular Waves ◽  
Wake Effect ◽  
Coupled Models ◽  
Propagation Models ◽  
Power Absorption ◽  
Structure Interaction ◽  
Wake Effects ◽  
Wave Structure Interaction

In the recent years, the potential impact of wave energy converter (WEC) arrays on the surrounding wave field has been studied using both phase-averaging and phase-resolving wave propagation models. Obtaining understanding of this impact is important because it may affect other users in the sea or on the coastline. However, in these models a parametrization of the WEC power absorption is often adopted. This may lead to an overestimation or underestimation of the overall WEC array power absorption, and thus to an unrealistic estimation of the potential WEC array impact. WEC array power absorption is a result of energy extraction from the incoming waves, and thus wave height decrease is generally observed downwave at large distances (the so-called “wake” or “far-field” effects). Moreover, the power absorption depends on the mutual interactions between the WECs of an array (the so-called “near field” effects). To deal with the limitations posed by wave propagation models, coupled models of recent years, which are nesting wave-structure interaction solvers into wave propagation models, have been used. Wave-structure interaction solvers can generally provide detailed hydrodynamic information around the WECs and a more realistic representation of wave power absorption. Coupled models have shown a lower WEC array impact in terms of wake effects compared to wave propagation models. However, all studies to date in which coupled models are employed have been performed using idealized long-crested waves. Ocean waves propagate with a certain directional spreading that affects the redistribution of wave energy in the lee of WEC arrays, and thus gaining insight wake effect for irregular short-crested sea states is crucial. In our research, a new methodology is introduced for the assessment of WEC array wake effects for realistic sea states. A coupled model is developed between the wave-structure interaction solver NEMOH and the wave propagation model MILDwave. A parametric study is performed showing a comparison between WEC array wake effects for regular, long-crested irregular, and short-crested irregular waves. For this investigation, a nine heaving-point absorber array is used for which the wave height reduction is found to be up to 8% lower at 1.0 km downwave the WEC array when changing from long-crested to short-crested irregular waves. Also, an oscillating wave surge WEC array is simulated and the overestimation of the wake effects in this case is up to 5%. These differences in wake effects between different wave types indicates the need to consider short-crested irregular waves to avoid overestimating the WEC array potential impacts. The MILDwave-NEMOH coupled model has proven to be a reliable numerical tool, with an efficient computational effort for simulating the wake effects of two different WEC arrays under the action of a range of different sea states.

Internal flow mechanism in a supersonic expander-rotor

2021 ◽  
pp. 095441002110236
Author(s):  
Zhenyu Huang ◽  
Jingjun Zhong
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Flow Structure ◽  
Internal Flow ◽  
Leading Edge ◽  
Wave Structure ◽  
Oblique Shock ◽  
Expansion Wave ◽  
Oblique Shock Wave ◽  
Flow Mechanism

This article proposes a numerical investigation into the internal flow structure in the supersonic expander-rotor (SER). In order to reveal internal flow mechanism, the significant influencing factors in the flow structure are identified, and the solutions to improving the integrated performance of the SER are developed. According to the numerical results, the wave structure of the expansion wave and the oblique shock wave is what characterizes the flow in the mainstream region of the SER. In addition, the expansion wave and the oblique shock wave impose control on the pattern of static pressure distribution in the 3-D channel and then the 3-D flow structure. The formation and breakdown of the tip leakage vortex are the main form that the motion of vortex takes in the SER. The concentration, recirculation, and separation of the boundary layer; the low energy fluid mixing with mainstream; and the interaction between the oblique shock waves and the boundary layer are the crucial motion tracing near the endwall. Compared with the traditional turbines, the flow structures in the tip region of the SER are relatively simpler; the essential motion tracing is the airflow near the leading edge of the strake wall moving from the PS through the tip gap to the SS as a result of the transverse pressure difference.

scholarly journals Influence of Power Take-Off Modelling on the Far-Field Effects of Wave Energy Converter Farms

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 429
Author(s):  
Gael Verao Fernandez ◽  
Vasiliki Stratigaki ◽  
Nicolas Quartier ◽  
Peter Troch
Keyword(s):  
Wave Propagation ◽  
Coupled Model ◽  
Wave Structure ◽  
Propagation Model ◽  
Far Field ◽  
Energy Converter ◽  
Coupled Models ◽  
Structure Interaction ◽  
Field Effects ◽  
Wave Structure Interaction

The study of the potential impact of wave energy converter (WEC) farms on the surrounding wave field at long distances from the WEC farm location (also know as “far field” effects) has been a topic of great interest in the past decade. Typically, “far-field” effects have been studied using phase average or phase resolving numerical models using a parametrization of the WEC power absorption using wave transmission coefficients. Most recent studies have focused on using coupled models between a wave-structure interaction solver and a wave-propagation model, which offer a more complex and accurate representation of the WEC hydrodynamics and PTO behaviour. The difference in the results between the two aforementioned approaches has not been studied yet, nor how different ways of modelling the PTO system can affect wave propagation in the lee of the WEC farm. The Coastal Engineering Research Group of Ghent University has developed both a parameterized model using the sponge layer technique in the mild slope wave propagation model MILDwave and a coupled model MILDwave-NEMOH (NEMOH is a boundary element method-based wave-structure interaction solver), for studying the “far-field” effects of WEC farms. The objective of the present study is to perform a comparison between both numerical approaches in terms of performance for obtaining the “far-field” effects of two WEC farms. Results are given for a series of regular wave conditions, demonstrating a better accuracy of the MILDwave-NEMOH coupled model in obtaining the wave disturbance coefficient (Kd) values around the considered WEC farms. Subsequently, the analysis is extended to study the influence of the PTO system modelling technique on the “far-field” effects by considering: (i) a linear optimal, (ii) a linear sub-optimal and (iii) a non-linear hydraulic PTO system. It is shown that modelling a linear optimal PTO system can lead to an unrealistic overestimation of the WEC motions than can heavily affect the wave height at a large distance in the lee of the WEC farm. On the contrary, modelling of a sub-optimal PTO system and of a hydraulic PTO system leads to a similar, yet reduced impact on the “far-field” effects on wave height. The comparison of the PTO systems’ modelling technique shows that when using coupled models, it is necessary to carefully model the WEC hydrodynamics and PTO behaviour as they can introduce substantial inaccuracies into the WECs’ motions and the WEC farm “far-field” effects.

An Experimental Setup for Idealised Studies on Transition to Turbulence on a Generic Compressor Outlet Guide Vane

2018 ◽  
Author(s):  
Jens H. M. Fransson ◽  
Santhosh B. Mamidala ◽  
Bengt E. G. Fallenius ◽  
Hans Mårtensson ◽  
Fredrik Wallin
Keyword(s):  
Large Scale ◽  
Guide Vane ◽  
Three Dimensional ◽  
Leading Edge ◽  
Transition To Turbulence ◽  
Experimental Setup ◽  
Reference Case ◽  
Total Drag ◽  
Flow Phenomena ◽  
Tunnel Design

The understanding of flow phenomena in turbomachinery has come far with respect to three-dimensional flow patterns and pressure distributions. Much is due to improved measurements and a continuously evolving fidelity in computational fluid dynamics (CFD). Turbulence and transition in boundary layers are two classical areas where improvements in modeling are desired and where experimental validation is required. Apart from this, fundamental improvements in efficiency can be obtained by developing experimental resources where technologies affecting transition can be studied. The reduction in friction drag can be considerable if the transition to turbulence can be delayed. An experimental setup in an idealized configuration has been designed and built with the objective to study transition on a very large-scale guide vane profile at low speed. The purpose of the rig is to enable high quality fundamental studies of technologies to delay transition, but also to see how effects of manufacturing or other constraints may affect the boundary layer. In the present paper we report the first validation of the experimental setup, by comparing the first test results to CFD calculations performed during the rig design, i.e. no post-calculations with experimental data as input to the simulations have been done yet. The pressure distribution is in line with the design intent, which is a good indicator that the tunnel design is suitable for the intended purpose. At last we report some velocity measurements performed in the wake and we calculate the total drag based on the wake velocity deficit for various Reynolds numbers and with and without turbulence tripping tape. We illustrate that a two dimensional tripping around 7% of the chord from the leading edge can increase the total drag by 50% with respect to the reference case without tripping tape.

Ice-mass changes in Aurora basin, East Antarctica, in coupled and uncoupled ice-ocean simulations

2021 ◽  
Author(s):  
Konstanze Haubner ◽  
Guillian Van Achter ◽  
Charles Pelletier ◽  
Lars Zipf ◽  
Thierry Fichefet ◽  
...  
Keyword(s):  
Sea Level ◽  
Ocean Circulation ◽  
Ice Sheet ◽  
Sea Level Change ◽  
Coupling Scheme ◽  
Coupled Models ◽  
Level Change ◽  
Ice Velocity ◽  
Velocity Changes ◽  
Global Sea Level

<p>Ice mass loss of Greenland and Antarctic ice sheets is a major contributor to sea level change with an expected major impact on the world's infrastructures over the next decades. Therefore, precise estimates of sea level change are needed. However, estimates of future changes in sea level are either provided by earth system models, which rarely include ice sheet models, or by standalone ice sheet models. Hence, feedbacks between ice and atmosphere-ocean are overseen. Local scale coupled models help bridging this gap by estimating how feedbacks between the different earth systems affect global sea level estimates.</p><p>Here, we present results from a coupled simulation of the ocean-sea ice model NEMO3.6-LIM3 (1/24° grid ~ less than 2 km grid spacing) and the ice sheet model BISICLES (on 0.5 - 4km spatial resolution). The coupling routine is done via python code including variable exchange, pre- and post-processing, done offline every 3 months.</p><p>Simulated ice mass changes, grounding line position and ice velocity changes of this high-resolution coupling scheme (between 1993-2014) are compared to observations and results of uncoupled simulations. We further discuss which processes might be neglectable and which are the main drivers of ice velocity acceleration and changes in sub-shelf ocean circulation.</p>

Experimental Study of Deicing Process in an Airfoil Application

2013 ◽  
Author(s):  
Pablo Perez Pereira ◽  
Luis D. Vilar-Carrasquillo ◽  
Gerardo Carbajal
Keyword(s):  
Steady State ◽  
Flow Characteristics ◽  
Temperature Response ◽  
Leading Edge ◽  
Transient Temperature ◽  
Experimental Setup ◽  
Trailing Edge ◽  
Steady State Temperature ◽  
Fluid Flow Characteristics ◽  
Transient Temperature Response

A customized airfoil for deicing process was designed, built and tested in order to investigate the effect of icing on the airfoil and the process of removing it by heating processed. A numerical simulation was performed to provide more details of the fluid flow characteristics of the presence of the ice and the temperature distribution on the airfoil when it reached the steady state conditions. An experimental setup was developed to measure and record the transient temperature response on the trailing and leading edge respectively. The experimental results suggest that from a minimum temperature of −10°C on the trailing edge, and 0°C in the leading edge with ice on the surface, the time to reach the steady state temperature of 46°C in the leading edge and 38°C in the trailing edge was close to 8 minutes approximately.

scholarly journals Design and Development of an Experimental Setup of Electrically Powered Spinning Rotor Blades in Icing Wind Tunnel and Preliminary Testing with Surface Coatings as Hybrid Protection Solution

Aerospace ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 98
Author(s):  
Eric Villeneuve ◽  
Caroline Blackburn ◽  
Christophe Volat
Keyword(s):  
Wind Tunnel ◽  
Power Consumption ◽  
Leading Edge ◽  
Surface Coatings ◽  
Small Scale ◽  
Experimental Setup ◽  
Preliminary Testing ◽  
Rotating Blades ◽  
Protection Systems ◽  
Ice Shedding

In order to study ice protection systems for rotating blades, a new experimental setup has been developed at the Anti-Icing Materials International Laboratory (AMIL). This system consists of two small-scale rotating blades in a refrigerated icing wind tunnel where atmospheric icing can be simulated. Power is brought to the blades through a slip ring, through which the signals of the different sensors that are installed on the blades also pass. As demonstrated by the literature review, this new setup will address the need of small-scale wind tunnel testing on electrically powered rotating blades. To test the newly designed apparatus, preliminary experimentation is done on a hybrid ice protection system. Electrothermal protection is combined with different surface coatings to measure the impact of those coatings on the power consumption of the system. In anti-icing mode, the coatings tested did not reduce the power consumption on the system required to prevent ice from accumulating on the leading edge. The coatings however, due to their hydrophobic/superhydrophobic nature, reduced the power required to prevent runback ice accumulation when the leading edge was protected. One of the coatings did not allow any runback accumulation, limiting the power to protect the whole blades to the power required to protect solely the leading edge, resulting in a potential 40% power reduction for the power consumption of the system. In de-icing mode, the results with all the substrates tested showed similar power to achieve ice shedding from the blade. Since the coatings tested have a low icephobicity, it would be interesting to perform additional testing with icephobic coatings. Also, a small unheated zone at the root of the blade prevented complete ice shedding from the blade. A small part of the ice layer was left on the blade after testing, meaning that a cohesive break had to occur within the ice layer, and therefore impacting the results. Improvements to the setup will be done to remedy the situation. Those preliminary testing performed with the newly developed test setup have demonstrated the potential of this new device which will now allow, among other things, to measure heat transfer, force magnitudes, ice nucleation, and thermal equilibrium during ice accretion, with different innovative thermal protection systems (conductive coating, carbon nanotubes, impulse, etc.) as well as mechanical systems. The next step, following the improvements, is to measure forced convection on a thermal ice protection system with and without precipitation and to test mechanical ice protection systems.

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