CFD Modeling of Surface Roughness in Laminar Flow

2004 ◽  
Author(s):  
Mounir Ibrahim ◽  
Pavan Veluri ◽  
Roy Tew ◽  
David Gedeon ◽  
T. Simon
Keyword(s):  
Surface Roughness ◽  
Laminar Flow ◽  
Cfd Modeling

scholarly journals Computational Analysis of Propulsion Performance of Modified Pitching Motion Airfoils in Laminar Flow

2014 ◽  
Vol 2014 ◽  
pp. 1-13
Author(s):  
Yonghui Xie ◽  
Kun Lu ◽  
Di Zhang ◽  
Gongnan Xie
Keyword(s):  
Laminar Flow ◽  
Cfd Modeling ◽  
Shape Effect ◽  
Optimal Range ◽  
Propulsive Efficiency ◽  
Pitching Motion ◽  
Propulsion Performance ◽  
Reduced Frequency ◽  
Thrust Generation ◽  
The Cost

The thrust generation performance of airfoils with modified pitching motion was investigated by computational fluid dynamics (CFD) modeling two-dimensional laminar flow at Reynolds number of 104. The effect of shift distance of the pitch axis outside the chord line(R), reduced frequency(k), pitching amplitude(θ), pitching profile, and airfoil shape (airfoil thickness and camber) on the thrust generated and efficiency were studied. The results reveal that the increase inRandkleads to an enhancement in thrust generation and a decrease in propulsive efficiency. Besides, there exists an optimal range ofθfor the maximum thrust and the increasingθinduces a rapid decrease in propulsive efficiency. Six adjustable parameters(K)were employed to realize various nonsinusoidal pitching profiles. An increase inKresults in more thrust generated at the cost of decreased propulsive efficiency. The investigation of the airfoil shape effect reveals that there exists an optimal range of airfoil thickness for the best propulsion performance and that the vortex structure is strongly influenced by the airfoil thickness, while varying the camber or camber location of airfoil sections offers no benefit in thrust generation over symmetric airfoil sections.

scholarly journals Experimental Study on Liquid Flow and Heat Transfer in Rough Microchannels

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Xuan Zhang ◽  
Taocheng Zhao ◽  
Suchen Wu ◽  
Feng Yao
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Cross Section ◽  
Liquid Flow ◽  
Flow And Heat Transfer ◽  
Section Shape ◽  
Poiseuille Number

Although roughness is negligible for laminar flow through tubes in classic fluid mechanics, the surface roughness may play an important role in microscale fluid flow due to the large ratio of surface area to volume. To further verify the influence of rough surfaces on microscale liquid flow and heat transfer, a performance test system of heat transfer and liquid flow was designed and built, and a series of experimental examinations are conducted, in which the microchannel material is stainless steel and the working medium is methanol. The results indicate that the surface roughness plays a significant role in the process of laminar flow and heat transfer in microchannels. In microchannels with roughness characteristics, the Poiseuille number of liquid laminar flow relies not only on the cross section shape of the rough microchannels but also on the Reynolds number of liquid flow. The Poiseuille number of liquid laminar flow in rough microchannels increases with increasing Reynolds number. In addition, the Nusselt number of liquid laminar heat transfer is related not only to the cross section shape of a rough microchannel but also to the Reynolds number of liquid flow, and the Nusselt number increases with increasing Reynolds number.

Parametric Study of Phase Change Suspension Flow in Microchannels

2003 ◽  
Author(s):  
Y. L. Hao ◽  
Y.-X. Tao
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Phase Change ◽  
Flow Condition ◽  
Computer Code ◽  
Cfd Modeling ◽  
Transfer Coefficients ◽  
Circular Duct ◽  
Heat Transfer Coefficients ◽  
Melting Region

A continuum model is applied to the numerical simulation of the laminar hydrodynamic and heat-transfer characteristics of suspension with phase change material (PCM) particles in a microchannel. The analytical/numerical formulation based on CFD modeling technique, and the computer code is developed. Local wall-to-suspension heat transfer coefficients are calculated by the simultaneous solution of the conservation of mass, momentum and thermal energy equations. By providing detailed information on the local behavior of the wall-to-suspension heat transfer coefficients, preliminary calculations expose that there exists a particle-depleted layer next to the wall under the laminar flow condition. It plays an important role on the heat transfer between the suspension and the wall under the laminar flow condition. The heat transfer coefficient increases and reaches a peak value in the melting region. The benefits on the enhancement of heat transfer and the reduction of wall temperature and mean temperature by employing the MCPCM particle are mainly in the melting region. The preliminary results agree very well with the experimental observations and measurement on the flow and heat transfer of microencapsulated PCM slurry in circular duct. It interprets the observation in the literature where heat transfer between the suspension and the wall is weaker in non-melting region and melted region than that between the pure fluid and the wall for laminar flow conditions.

Role of surface roughness characterized by fractal geometry on laminar flow in microchannels

2009 ◽  
Vol 80 (2) ◽  
Author(s):  
Yongping Chen ◽  
Chengbin Zhang ◽  
Mingheng Shi ◽  
G. P. Peterson
Keyword(s):  
Surface Roughness ◽  
Laminar Flow ◽  
Fractal Geometry

Mount Etna and the 1971 eruption - Rheological features of the 1971 Mount Etna lavas

1973 ◽  
Vol 274 (1238) ◽  
pp. 99-106 ◽  
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Mechanical Energy ◽  
Critical Value ◽  
Heat Energy ◽  
Mount Etna ◽  
Two Dimensional ◽  
Spiral Motion ◽  
Rapid Transition

Rheological studies on the 1971 M ount Etna lavas indicate they underwent rapid transition from Newtonian to non-Newtonian fluids near their point of emission and that the non-Newtonian regime may be coincidental with high mechanical energy/low heat energy regime further from the boccas. Darcy’s equation quantifies the surface roughness of channels using the Chezy coefficient and is plotted against Reynolds number on a Stanton diagram. The relation is linear, and the critical value Re0 is not exceeded, proving wholly laminar flow. The lava underwent a divergent, twin spiral motion involving two dimensional laminar flow. Convergent, twin spiral motion occurred only where lava passed through a constriction at a relatively high velocity.

scholarly journals Technical note: Influence of surface roughness and local turbulence on coated-wall flow tube experiments for gas uptake and kinetic studies

2018 ◽  
Vol 18 (4) ◽  
pp. 2669-2686 ◽  
Author(s):  
Guo Li ◽  
Hang Su ◽  
Uwe Kuhn ◽  
Hannah Meusel ◽  
Markus Ammann ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Laminar Flow ◽  
Coating Thickness ◽  
Kinetic Studies ◽  
Flow Conditions ◽  
Flow Tube ◽  
Critical Height ◽  
Gas Uptake ◽  
Turbulence Effects ◽  
Wall Flow

Abstract. Coated-wall flow tube reactors are frequently used to investigate gas uptake and heterogeneous or multiphase reaction kinetics under laminar flow conditions. Coating surface roughness may potentially distort the laminar flow pattern, induce turbulence and introduce uncertainties in the calculated uptake coefficient based on molecular diffusion assumptions (e.g., Brown/Cooney–Kim–Davis (CKD)/Knopf–Pöschl–Shiraiwa (KPS) methods), which has not been fully resolved in earlier studies. Here, we investigate the influence of surface roughness and local turbulence on coated-wall flow tube experiments for gas uptake and kinetic studies. According to laminar boundary theory and considering the specific flow conditions in a coated-wall flow tube, we derive and propose a critical height δc to evaluate turbulence effects in the design and analysis of coated-wall flow tube experiments. If a geometric coating thickness δg is larger than δc, the roughness elements of the coating may cause local turbulence and result in overestimation of the real uptake coefficient (γ). We further develop modified CKD/KPS methods (i.e., CKD-LT/KPS-LT) to account for roughness-induced local turbulence effects. By combination of the original methods and their modified versions, the maximum error range of γCKD (derived with the CKD method) or γKPS (derived with the KPS method) can be quantified and finally γ can be constrained. When turbulence is generated, γCKD or γKPS can bear large difference compared to γ. Their difference becomes smaller for gas reactants with lower uptake (i.e., smaller γ) and/or for a smaller ratio of the geometric coating thickness to the flow tube radius (δg ∕ R0). On the other hand, the critical height δc can also be adjusted by optimizing flow tube configurations and operating conditions (i.e., tube diameter, length, and flow velocity), to ensure not only unaffected laminar flow patterns but also other specific requirements for an individual flow tube experiment. We use coating thickness values from previous coated-wall flow tube studies to assess potential roughness effects using the δc criterion. In most studies, the coating thickness was sufficiently small to avoid complications, but some may have been influenced by surface roughness and local turbulence effects.

scholarly journals Rapid prototyping method for 3D PDMS microfluidic devices using a red femtosecond laser

2020 ◽  
Vol 12 (12) ◽  
pp. 168781402098271
Author(s):  
Mozafar Saadat ◽  
Marie Taylor ◽  
Arran Hughes ◽  
Amir M Hajiyavand
Keyword(s):  
Surface Roughness ◽  
Laminar Flow ◽  
Femtosecond Laser ◽  
Rapid Prototyping ◽  
Microfluidic Devices ◽  
Thermal Curing ◽  
Ramp Test ◽  
Mould Surface ◽  
Polished Metal ◽  
Pdms Device

A rapid prototyping technique is demonstrated which uses a red femtosecond laser to produce a metallic mould which is then directly used for the replica moulding of PDMS. The manufacturing process can be completed in less than 6 h making it a viable technique for testing new designs quickly. The technique is validated by creating a microfluidic device with channels of height and depth of 300 µm, with a ramp test structure where the height and width of the channels reduces to 100 µm to demonstrate the techniques 3D capabilities. The resulting PDMS device was easily removed from the metallic mould and closely replicated the shape aside the expected shrinkage during thermal curing. As the technique uses a single replica process, the surface roughness at the base of the channels corresponds to the un-ablated polished metal mould, resulting in a very low surface roughness of 0.361 nm. The ablated metallic mould surface corresponds to the top of the PDMS device, which is bonded to glass and does not affect the flow within the channels, reducing the need for optimisation of laser parameters. Finally, the device is validated by demonstrating laminar flow with the no-slip condition.

Characterization of Surface Roughness Effects on Laminar Flow in Microchannels by Using Fractal Cantor Structures

2009 ◽  
Author(s):  
Chengbin Zhang ◽  
Yongping Chen ◽  
Panpan Fu ◽  
Mingheng Shi
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Fractal Dimension ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Flow Direction ◽  
Roughness Effects ◽  
Relative Roughness ◽  
Smooth Channel

The fractal characterization of the topography of rough surfaces by using Cantor set structures is introduced in this paper. Based on the fractal Cantor surface, a model of laminar flow in rough microchannels is developed and numerically analyzed to study the characterization of surface roughness effects on laminar flow. The effects of Reynolds number, relative roughness, and fractal dimension on laminar flow are all discussed. The results indicate that the presence of roughness leads to the form of the detachment, and eddy generation is observed at the shadow of the roughness elements. The pressure drop in the rough channel along the flow direction is no longer in a linear fashion and larger than that in the smooth channel. The fluctuation characteristic of pressure drop along the stream, which is due to the vortex formation at the wall, is found. Differing from the smooth channel, the Poiseuille number for laminar flow in rough microchannels is no longer only dependent on the cross-sectional shape of the channel, but also strongly influenced by the Reynolds number, relative roughness and fractal dimension of the surface.

MODELING OF THE MINIMIZED TWO-PHASE FLOW FRICTIONAL PRESSURE DROP IN A SMALL TUBE WITH DIFFERENT CORRELATIONS

2016 ◽  
Vol 78 (6-11) ◽  
Author(s):  
Qais Abid Yousif ◽  
Normah Mohd-Ghazali ◽  
Nor Atiqah Zolpakar ◽  
Sentot Novianto ◽  
Agus Sujiantro Pamitran ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Friction Factor ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Flow Conditions ◽  
Two Phase ◽  
Frictional Pressure Drop

The major parameters of interest in heat transfer research are the refrigerant charge, pressure drop, and heat transfer capacity. Smaller channels reduce the refrigerant charge with higher heat transfer capability due to the increased in surface area to volume ratio but at the expense of a higher pressure drop. Differences between the predicted and experimental frictional pressure drop of two-phase flow in small tubes have frequently been discussed. Factors that could have contributed to that effect have been attributed to the correlations used to model the flow, some being modified from the originals developed for a macro system. Experimental test-rigs have varied in channel geometry, refrigerant type, and flow conditions. Thousands of data have been collected to find a common point among the differences. This paper reports an investigation of four different two-phase friction factor correlations used in the modeling of the frictional two-phase flow pressure drop of refrigerant R-22. One had been specifically developed for laminar flow in a smooth channel, another was modified from a laminar flow in a smooth pipe to be used for a rough channel, and two correlations are specific for turbulent flow that consider internal pipe surface roughness. Genetic algorithm, an optimization scheme, is used to search for the minimum friction factor and minimum frictional pressure drop under optimized conditions of the mass flux and vapor quality. The results show that a larger pressure drop does come with a smaller channel. A large discrepancy exists between the correlations investigated; between the ones that does not consider surface roughness and that which does, as well as between flow under laminar and turbulent flow conditions.

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