Note on Water Drag on Sea Ice for Different Surface Roughness

1991 ◽  
Vol 113 (1) ◽  
pp. 67-69
Author(s):  
D. Myrhaug
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Shear Stress ◽  
Sea Ice ◽  
Turbulent Flow ◽  
Drag Coefficient ◽  
Turbulent Flows ◽  
Surface Shear Stress ◽  
Surface Shear ◽  
Ice Surface

The approach in Myrhaug [1], where a simple analytical theory describing the motion in a turbulent planetary boundary layer near a rough seabed was presented, is extended to smooth and transitional smooth-to-rough turbulent flow. An inverted boundary layer similar to that at the seabed is applicable under the sea ice. The water drag coefficient at the ice surface and the direction of the surface shear stress are presented for rough, smooth and transitional turbulent flows.

scholarly journals Dependency of particle size distribution at dust emission on friction velocity and atmospheric boundary-layer stability

2020 ◽  
Vol 20 (21) ◽  
pp. 12939-12953
Author(s):  
Yaping Shao ◽  
Jie Zhang ◽  
Masahide Ishizuka ◽  
Masao Mikami ◽  
John Leys ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Particle Size ◽  
Probability Distribution ◽  
Particle Size Distribution ◽  
Atmospheric Boundary Layer ◽  
Size Distribution ◽  
Turbulent Flows ◽  
Friction Velocity ◽  
Surface Shear Stress ◽  
Surface Shear

Abstract. Particle size distribution of dust at emission (dust PSD) is an essential quantity to estimate in dust studies. It has been recognized in earlier research that dust PSD is dependent on soil properties (e.g. whether soil is sand or clay) and friction velocity, u∗, which is a surrogate for surface shear stress and a descriptor for saltation-bombardment intensity. This recognition has been challenged in some recent papers, causing a debate on whether dust PSD is “invariant” and the search for its justification. In this paper, we analyse the dust PSD measured in the Japan Australian Dust Experiment and show that dust PSD is dependent on u∗ and on atmospheric boundary-layer (ABL) stability. By simple theoretical and numerical analysis, we explain the two reasons for the latter dependency, which are both related to enhanced saltation bombardment in convective turbulent flows. First, u∗ is stochastic and its probability distribution profoundly influences the magnitude of the mean saltation flux due to the non-linear relationship between saltation flux and u∗. Second, in unstable conditions, turbulence is usually stronger, which leads to higher saltation-bombardment intensity. This study confirms that dust PSD depends on u∗ and, more precisely, on the probability distribution of u∗, which in turn is dependent on ABL stability; consequently, dust PSD is also dependent on ABL. We also show that the dependency of dust PSD on u∗ and ABL stability is made complicated by soil surface conditions. In general, our analysis reinforces the basic conceptual understanding that dust PSD depends on saltation bombardment and inter-particle cohesion.

Experimental approaches towards interpreting dolphin-stimulated bioluminescence.

1998 ◽  
Vol 201 (9) ◽  
pp. 1447-1460 ◽  
Author(s):  
J Rohr ◽  
M I Latz ◽  
S Fallon ◽  
J C Nauen ◽  
E Hendricks
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Flow Visualization ◽  
Leading Edge ◽  
Field Studies ◽  
Flow Speed ◽  
The Body ◽  
Surface Shear Stress ◽  
Literature Report ◽  
Surface Shear

Flow-induced bioluminescence provides a unique opportunity for visualizing the flow field around a swimming dolphin. Unfortunately, previous descriptions of dolphin-stimulated bioluminescence have been largely anecdotal and often conflicting. Most references in the scientific literature report an absence of bioluminescence on the dolphin body, which has been invariably assumed to be indicative of laminar flow. However, hydrodynamicists have yet to find compelling evidence that the flow remains laminar over most of the body. The present study integrates laboratory, computational and field approaches to begin to assess the utility of using bioluminescence as a method for flow visualization by relating fundamental characteristics of the flow to the stimulation of naturally occurring luminescent plankton. Laboratory experiments using fully developed pipe flow revealed that the bioluminescent organisms identified in the field studies can be stimulated in both laminar and turbulent flow when shear stress values exceed approximately 0.1 N m-2. Computational studies of an idealized hydrodynamic representation of a dolphin (modeled as a 6:1 ellipsoid), gliding at a speed of 2 m s-1, predicted suprathreshold surface shear stress values everywhere on the model, regardless of whether the boundary layer flow was laminar or turbulent. Laboratory flow visualization of a sphere demonstrated that the intensity of bioluminescence decreased with increasing flow speed due to the thinning of the boundary layer, while flow separation caused a dramatic increase in intensity due to the significantly greater volume of stimulating flow in the wake. Intensified video recordings of dolphins gliding at speeds of approximately 2 m s-1 confirmed that brilliant displays of bioluminescence occurred on the body of the dolphin. The distribution and intensity of bioluminescence suggest that the flow remained attached over most of the body. A conspicuous lack of bioluminescence was often observed on the dolphin rostrum and melon and on the leading edge of the dorsal and pectoral fins, where the boundary layer is thought to be thinnest. To differentiate between effects related to the thickness of the stimulatory boundary layer and those due to the latency of the bioluminescence response and the upstream depletion of bioluminescence, laboratory and dolphin studies of forced separation and laminar-to-turbulent transition were conducted. The observed pattern of stimulated bioluminescence is consistent with the hypothesis that bioluminescent intensity is directly related to the thickness of the boundary layer.

scholarly journals On a Homotopy Perturbation Treatment of Steady Laminar Forced Convection Flow over a Nonlinearly Stretching Porous Sheet

2014 ◽  
Vol 2014 ◽  
pp. 1-8
Author(s):  
Nemat Dalir ◽  
Salman Nourazar
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Forced Convection ◽  
Convection Flow ◽  
Surface Shear Stress ◽  
Surface Shear ◽  
Suction Parameter ◽  
Sheet Surface ◽  
Homotopy Perturbation ◽  
Laminar Forced Convection

The steady two-dimensional laminar forced convection boundary layer flow of an incompressible viscous Newtonian fluid over a nonlinearly stretching porous (permeable) sheet with suction is considered. The sheet’s permeability is also considered to be nonlinear. The boundary layer equations are transformed by similarity transformations to a nonlinear ordinary differential equation (ODE). Then the homotopy perturbation method (HPM) is used to solve the resultant nonlinear ODE. The dimensionless entrainment parameter and the dimensionless sheet surface shear stress are obtained for various values of the suction parameter and the nonlinearity factor of sheet stretching and permeability. The results indicate that the dimensionless sheet surface shear stress decreases with the increase of suction parameter. The results of present HPM solution are compared to the values obtained in a previous study by the homotopy analysis method (HAM). The HPM results show that they are in good agreement with the HAM results within 2% error.

Compressor Wake/Leading-Edge Interactions at Off Design Incidences

2008 ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Robert J. Miller
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Flow Field ◽  
Leading Edge ◽  
Flow Coefficient ◽  
Surface Shear Stress ◽  
Momentum Thickness ◽  
Surface Shear ◽  
Time Resolved ◽  
Edge Flow

In this paper, the effects of wake/leading-edge interactions were studied at off-design conditions. Measurements were performed on the stator-blade suction surface at midspan. The leading-edge flow-field was investigated using hotwire micro-traverses, hotfilm surface shear-stress sensors and pressure micro-tappings. The trailing-edge flow-field was investigated using hotwire boundary-layer traverses. Unsteady CFD calculations were also performed to aid the interpretation of the results. At low flow coefficients, the time-averaged momentum thickness of the leading-edge boundary layer was found to rise as the flow coefficient was reduced. The time-resolved momentum-thickness rose due to the interaction of the incoming rotor wake. As the flow coefficient was reduced, the incoming wakes increased in pitch-wise extent, velocity deficit and turbulence intensity. This increased both the time-resolved rise in the momentum thickness and the turbulent spot production within the wake affected boundary-layer. Close to stall, a drop in the leading-edge momentum thickness was observed in-between wake events. This was associated with the formation of a leading-edge separation bubble in-between wake events. The wake interaction with the bubble gave rise to a shedding phenomenon, which produced large length scale disturbances in the surface shear stress.

scholarly journals Heat transfer analysis in the time-dependent axisymmetric stagnation point flow over a lubricated surface

2018 ◽  
Vol 22 (6 Part A) ◽  
pp. 2483-2492 ◽  
Author(s):  
Khalid Mahmood ◽  
Muhammad Sajid ◽  
Nasir Ali ◽  
Tariq Javed
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Shear Stress ◽  
Partial Differential Equations ◽  
Differential Equations ◽  
Time Dependent ◽  
Surface Shear Stress ◽  
Partial Differential ◽  
Surface Shear ◽  
Flow And Heat Transfer

In this paper time-dependent, 2-D, axisymmetric flow and heat transfer of a viscous incompressible fluid impinging orthogonally on a disc is examined. The disc is lubricated with a thin layer of power-law fluid of variable thickness. It is assumed that surface temperature of the disc is time-dependent. Continuity of velocity and shear stress at the interface layer between the fluid and the lubricant has been imposed to obtain the solution of the governing partial differential equations. The set of partial differential equations is reduced into ordinary differential equations by suitable transformations and are solved numerically by using Keller-Box method. Solutions are presented in the form of graphs and tables in order to examine the influence of pertinent parameters on the flow and heat transfer characteristics. An increase in lubrication results in the reduction of surface shear stress and consequently viscous boundary layer becomes thin. However, the thermal boundary layer thickness increases by increasing lubrication. It is further observed that surface shear stress and heat transfer rate at the wall enhance due to unsteadiness. The results for the steady case are deduced from the present solutions and are found in good agreement with the existing results in the literature.

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