2D Experimental Study of Waves and Current Contribution to the Nearbed Velocities and Shear Stresses Field

2004 ◽  
Author(s):  
M. R. Delgado Blanco ◽  
T. De Mulder ◽  
M. Willems ◽  
R. Banasiak ◽  
R. Verhoeven ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Field Data ◽  
Oscillatory Flow ◽  
Roughness Length ◽  
Numerical Models ◽  
Shear Stresses ◽  
Friction Forces ◽  
Current Contribution ◽  
Laboratory Flume ◽  
Waves And Currents

Most of what is known about flow under waves and currents has been deduced from numerical models and not always validated. Absence of accurate experimental and field data, including measurements within the boundary layer or in its vicinity, makes the observation and study of the interaction between steady and oscillatory flow together with model validation difficult. A series of 2D experiments has been done in a laboratory flume. Velocity profiles obtained under different conditions have been analyzed. In addition, a simple 1DV model for turbulent boundary layer simulation has been used. Computed near bed velocities and roughness length are compared with experimental results. By means of three methods based on experimental and numerical results, variations of friction forces as a result of the interaction between the oscillatory and the steady components are evaluated.

Estimating Turbulence and Shear Stress under Regular Waves from ADV Data

2012 ◽  
Vol 212-213 ◽  
pp. 1083-1091
Author(s):  
Zheng Xiao ◽  
Chao Shen ◽  
Zhi Xin Guan ◽  
Yuan Li ◽  
Rui Min Ji
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Bottom Boundary Layer ◽  
Wave Flow ◽  
Shear Stresses ◽  
Coastal Morphology ◽  
Bottom Boundary ◽  
Sand Ripples ◽  
Laboratory Flume ◽  
Layer Flow

The boundary layer flow determines the bottom shear stresses, which is key point for sediment transport and thereby the evolution of coastal morphology. The structure of the bottom boundary layer in coastal seas has been of interest to oceanographers for many years. In the paper Acoustic Doppler velocimeter (ADV) technique is applied to measure the bottom boundary layer under cnoidal waves in a laboratory flume with 40-m-long, 0.5-m-wide, and 0.8-m-deep.. Based on the high frequency turbulence signal collected, statistic parameters of cnoidal wave flow are calculated, compared and analyzed. The turbulent structure over plain bed and sand ripples bed are carefully studied. The turbulence intensity of near-bed velocities changes along depth of several phases in a period is analyzed. Turbulent Kinetic Energy Method (TKE Method) is used to estimate near-bed shear stress on flat and slope.

Non-Newtonian oscillatory layer flow, approximate solution

1979 ◽  
Vol 44 (10) ◽  
pp. 2908-2914 ◽  
Author(s):  
Ondřej Wein
Keyword(s):  
Boundary Layer ◽  
Approximate Solution ◽  
Galerkin Method ◽  
Horizontal Plane ◽  
Oscillatory Flow ◽  
Oscillatory Boundary Layer ◽  
Layer Flow ◽  
Pseudoplastic Liquid ◽  
The Galerkin Method

The problem of the oscillatory flow of pseudoplastic liquid in vicinity of the infinitely long horizontal plane is formulated in stresses. For Re i.e. for conditions of oscillatory boundary layer the problem is solved approximately by the Galerkin method.

scholarly journals Aspect Ratio Driven Relationship between Nozzle Internal Flow and Supersonic Jet Mixing

Aerospace ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 78
Author(s):  
Kalyani Bhide ◽  
Kiran Siddappaji ◽  
Shaaban Abdallah
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Nozzle Exit ◽  
Supersonic Jet ◽  
Internal Flow ◽  
Shear Stresses ◽  
Loss Mechanism ◽  
Potential Core ◽  
Jet Mixing ◽  
Aspect Ratios

This work attempts to connect internal flow to the exit flow and supersonic jet mixing in rectangular nozzles with low to high aspect ratios (AR). A series of low and high aspect ratio rectangular nozzles (design Mach number = 1.5) with sharp throats are numerically investigated using steady state Reynolds-averaged Navier−Stokes (RANS) computational fluid dynamics (CFD) with k-omega shear stress transport (SST) turbulence model. The numerical shadowgraph reveals stronger shocks at low ARs which become weaker with increasing AR due to less flow turning at the throat. Stronger shocks cause more aggressive gradients in the boundary layer resulting in higher wall shear stresses at the throat for low ARs. The boundary layer becomes thick at low ARs creating more aerodynamic blockage. The boundary layer exiting the nozzle transforms into a shear layer and grows thicker in the high AR nozzle with a smaller potential core length. The variation in the boundary layer growth on the minor and major axis is explained and its growth downstream the throat has a significant role in nozzle exit flow characteristics. The loss mechanism throughout the flow is shown as the entropy generated due to viscous dissipation and accounts for supersonic jet mixing. Axis switching phenomenon is also addressed by analyzing the streamwise vorticity fields at various locations downstream from the nozzle exit.

Measurements in a Turbulent Boundary Layer Over a d-Type Surface Roughness

1975 ◽  
Vol 42 (3) ◽  
pp. 591-597 ◽  
Author(s):  
D. H. Wood ◽  
R. A. Antonia
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Turbulent Boundary Layer ◽  
Turbulent Energy ◽  
Shear Stresses ◽  
Normal Velocity ◽  
Mean Velocity ◽  
Outer Flow ◽  
Intensity Measurements ◽  
Normal And Shear Stresses

Mean velocity and turbulence intensity measurements have been made in a fully developed turbulent boundary layer over a d-type surface roughness. This roughness is characterised by regular two-dimensional elements of square cross section placed one element width apart, with the cavity flow between elements being essentially isolated from the outer flow. The measurements show that this boundary layer closely satisfies the requirement of exact self-preservation. Distribution across the layer of Reynolds normal and shear stresses are closely similar to those found over a smooth surface except for the region immediately above the grooves. This similarity extends to distributions of third and fourth-order moments of longitudinal and normal velocity fluctuations and also to the distribution of turbulent energy dissipation. The present results are compared with those obtained for a k-type or sand grained roughness.

Endwall Boundary Layer Development in a Multistage Low-Speed Compressor With Tandem Stator Vanes

2021 ◽  
Author(s):  
Michael Hopfinger ◽  
Volker Gümmer
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Shear Stresses ◽  
Flow Area ◽  
Stage Design ◽  
Low Speed ◽  
Boundary Layer Development ◽  
Viscous Shear ◽  
Layer Development ◽  
Highly Loaded

Abstract The development of viscous endwall flow is of major importance when considering highly-loaded compressor stages. Essentially, all losses occurring in a subsonic compressor are caused by viscous shear stresses building up boundary layers on individual aerofoils and endwall surfaces. These boundary layers cause significant aerodynamic blockage and cause a reduction in effective flow area, depending on the specifics of the stage design. The presented work describes the numerical investigation of blockage development in a 3.5-stage low-speed compressor with tandem stator vanes. The research is aimed at understanding the mechanism of blockage generation and growth in tandem vane rows and across the entire compressor. Therefore, the blockage generation is investigated as a function of the operating point, the rotational speed and the inlet boundary layer thickness.

Sedimentation in Storage Tank Structures

1994 ◽  
Vol 29 (1-2) ◽  
pp. 363-372 ◽  
Author(s):  
Virginia R. Stovin ◽  
Adrian J. Saul
Keyword(s):  
Numerical Models ◽  
Effective Means ◽  
Design Guidelines ◽  
Laboratory Model ◽  
Shear Stresses ◽  
Model Situation ◽  
Combined Sewer ◽  
Urban Watercourse ◽  
Storage Structures ◽  
Selection Of

Although storage tanks provide an effective means of reducing the magnitude and frequency of combined sewer overflow discharges, and thereby of alleviating urban watercourse pollution, poorly designed storage structures frequently suffer from maintenance problems arising from sedimentation. The development of design guidelines that optimise the self-cleansing operation of storage structures is clearly a priority for urban drainage research. This paper describes a system that has been developed to study sediment deposition in laboratory model-scale storage structures. The patterns of deposition resulting from a selection of flow regimes are described, and the need for time-varying and time series storm tests is highlighted. Sedimentation patterns are shown to predominantly depend on the flow field, and the critical bed shear stresses for deposition and erosion in the model situation are identified. Hence, the potential application of numerical models to the design problem is discussed.

scholarly journals MEASUREMENT OF SEDIMENT SUSPENSION IN COMBINATIONS OF WAVES AND CURRENTS

1972 ◽  
Vol 1 (13) ◽  
pp. 55
Author(s):  
J. Kirkegarrd Jensen ◽  
Torben Sorenson
Keyword(s):  
Thin Layer ◽  
Concentration Profile ◽  
Field Data ◽  
Concentration Profiles ◽  
Sediment Suspension ◽  
Calculated Concentration ◽  
Waves And Currents ◽  
The Mean ◽  
Mean Concentration ◽  
Good Agreement

The paper describes a procedure for obtaining field data on the mean concentration of sediments in combination of waves and currents outside the breaker zone, as well as some results of such measurements. It is assumed that the current turbulence alone is responsible for the maintenance of the concentration profile above a thin layer close to the bottom, in which pick-up of sediments due to wave agitation takes place. This assumption gives a good agreement between field data and calculated concentration profiles.

scholarly journals Longitudinal Stress Gradients and Basal Shear Stress of a Temperate Valley Glacier

1979 ◽  
Vol 24 (90) ◽  
pp. 507-508 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Field Data ◽  
Numerical Models ◽  
Lateral Strain ◽  
Longitudinal Stress ◽  
Base Shear ◽  
Stress Gradients ◽  
Valley Glacier ◽  
Image Position

AbstractFor the first time field data from a temperate valley glacier, the Variegated Glacier, are used to investigate the behavior of longitudinal stress gradients predicted by the relation(1)whereHis the local depth, andysandybare the surface and bed elevations respectively. This equation is similar to one derived by Budd (1970) for plane strain-rate, to evaluate the importance of longitudinal stress gradients, but a shape factorfis included to account approximately for lateral strain-rate gradients. Predictive numerical models of valley glaciers require the local base shear stress to be known as accurately as possible. It has been argued on theoretical grounds that whenTis averaged over distances of more than five to ten times the depth, this term is negligible. At larger averaging scales, 2Gcan then be considered a correction to the simple geometric expression of base stress due to the presence of longitudinal stress gradients. Field data of velocity and geometry are used to evaluate the terms of Equation (1), whereτband 2Gare estimated asandat intervals of 100 m,Usis the measured surface center-line velocity,Aandnare the flow-law parameters, andis the surface longitudinal strain-rate. The expression for 2Gis an approximation proposed by Budd (1970).

scholarly journals Improving Radar Refractivity Retrieval by Considering the Change in the Refractivity Profile and the Varying Altitudes of Ground Targets

2016 ◽  
Vol 33 (5) ◽  
pp. 989-1004 ◽  
Author(s):  
Ya-Chien Feng ◽  
Frédéric Fabry ◽  
Tammy M. Weckwerth
Keyword(s):  
Boundary Layer ◽  
Data Quality ◽  
Temporal Change ◽  
Numerical Models ◽  
Vertical Gradient ◽  
Target Range ◽  
Constant Height ◽  
Measured Phase

AbstractAccurate radar refractivity retrievals are critical for quantitative applications, such as assimilating refractivity into numerical models or studying boundary layer and convection processes. However, the technique as originally developed makes some simplistic assumptions about the heights of ground targets () and the vertical gradient of refractivity (). In reality, the field of target phases used for refractivity retrieval is noisy because of varying terrain and introduces estimation biases. To obtain a refractivity map at a constant height above terrain, a 2D horizontal refractivity field at the radar height must be computed and corrected for altitude using an average . This is achieved by theoretically clarifying the interpretation of the measured phase considering the varying and the temporal change of . Evolving causes systematic refractivity biases, as it affects the beam trajectory, the associated target range, and the refractivity field sampled between selected targets of different heights. To determine and changes, a twofold approach is proposed: first, can be reasonably inferred based on terrain height; then, a new method of estimation is devised by using the property of the returned powers of a pointlike target at successive antenna elevations. The obtained shows skill based on in situ tower observation. As a result, the data quality of the retrieved refractivity may be improved with the newly added information of and .

Sign in / Sign up

Export Citation Format

Share Document