Experimental Investigation on Influence of Inclination and Curved Surface of Ship Bottom in Air Lubrication Method

2019 ◽  
Author(s):  
Chiharu Kawakita ◽  
Tatsuya Hamada
Keyword(s):  
Shear Stress ◽  
Drag Reduction ◽  
Energy Saving ◽  
Frictional Drag ◽  
Void Fraction Distribution ◽  
Air Lubrication ◽  
Fraction Distribution ◽  
Local Shear ◽  
Reduction Effect ◽  
Local Shear Stress

Abstract The air lubrication method, which mixes millimeter bubbles into the flow around the hull and reduces frictional resistance, is expected to have a large energy saving effect among a number of marine energy saving technologies. Concerning the frictional drag reduction effect using the air lubrication method, in this study, the frictional drag reduction effect was experimentally investigated for gas-liquid two phase flow considering the influence of inclination and curved surface of the ship bottom. Measurement of local shear stress and measurement of void fraction distribution near the wall surface were carried out and the correlation between local shear stress and local void fraction distribution was grasped.

Effect of Bubble Size on the Microbubble Drag Reduction of a Turbulent Boundary Layer

2003 ◽  
Author(s):  
Takafumi Kawamura ◽  
Yasuhiro Moriguchi ◽  
Hiroharu Kato ◽  
Akira Kakugawa ◽  
Yoshiaki Kodama
Keyword(s):  
Drag Reduction ◽  
Flow Velocity ◽  
Bubble Diameter ◽  
Average Diameter ◽  
Main Flow ◽  
Frictional Drag ◽  
The Third ◽  
Local Shear ◽  
Small Bubbles ◽  
Local Shear Stress

Three different methods have been investigated for generating microbubbles to control the bubble diameter separately from the main flow velocity. The first two methods achieve this by adjusting the local shear stress where bubbles are generated, while the third method uses foaming of dissolved air to generate very small bubbles. The average diameter of bubbles was successfully controlled by the first two method within the range of 0.5–2 mm for the fixed main flow velocity of U = 3 m/s, while the very small bubbles of 20–40 μm were generated by the third method. The influence of the bubble diameter on the frictional drag reduction was found to be insignificant for the diameter range of 0.5–2 mm, while we also obtained experimental results suggesting that smaller bubbles on the order of 10 μm in diameter can be effective for the drag reduction.

Roughness Influence on Turbulent Flow Through Annular Seals

1994 ◽  
Vol 116 (2) ◽  
pp. 321-328 ◽  
Author(s):  
Victor Lucas ◽  
Sterian Danaila ◽  
Olivier Bonneau ◽  
Jean Freˆne
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Dynamic Characteristics ◽  
Reynolds Equation ◽  
Mixing Length ◽  
Local Shear ◽  
Wall Shear ◽  
Local Shear Stress

This paper deals with an analysis of turbulent flow in annular seals with rough surfaces. In this approach, our objectives are to develop a model of turbulence including surface roughness and to quantify the influence of surface roughness on turbulent flow. In this paper, in order to simplify the analysis, the inertial effects are neglected. These effects will be taken into account in a subsequent work. Consequently, this study is based on the solution of Reynolds equation. Turbulent flow is solved using Prandtl’s turbulent model with Van Driest’s mixing length expression. In Van Driest’s model, the mixing length depends on wall shear stress. However there are many numerical problems in evaluating this wall shear stress. Therefore, the goal of this work has been to use the local shear stress in the Van Driest’s model. This derived from the work of Elrod and Ng concerning Reichardt’s mixing length. The mixing length expression is then modified to introduce roughness effects. Then, the momentum equations are solved to evaluate the circumferential and axial velocity distributions as well as the turbulent viscosity μ1 (Boussinesq’s hypothesis) within the film. The coefficients of turbulence kx and kz, occurring in the generalized Reynolds’ equation, are then calculated as functions of the flow parameters. Reynolds’ equation is solved by using a finite centered difference method. Dynamic characteristics are calculated by exciting the system numerically, with displacement and velocity perturbations. The model of Van Driest using local shear stress and function of roughness has been compared (for smooth seals) to the Elrod and Ng theory. Some numerical results of the static and dynamic characteristics of a rough seal (with the same roughness on the rotor as on the stator) are presented. These results show the influence of roughness on the dynamic behavior of the shaft.

scholarly journals Stress-gradient Coupling in Glacier Flow: IV. Effects of the “T” Term

1986 ◽  
Vol 32 (112) ◽  
pp. 342-349 ◽  
Author(s):  
Barclay Kamb ◽  
Keith A. Echelmeyer
Keyword(s):  
Shear Stress ◽  
Coupling Theory ◽  
Longitudinal Stress ◽  
Longitudinal Flow ◽  
Stress Gradients ◽  
Flow Coupling ◽  
Flow Response ◽  
Longitudinal Variations ◽  
Local Shear ◽  
Local Shear Stress

AbstractThe “T term” in the longitudinal stress-equilibrium equation for glacier mechanics, a double y-integral of ∂2τxy/∂x2 where x is a longitudinal coordinate and y is roughly normal to the ice surface, can be evaluated within the framework of longitudinal flow-coupling theory by linking the local shear stress τxy at any depth to the local shear stress τB at the base, which is determined by the theory. This approach leads to a modified longitudinal flow-coupling equation, in which the modifications deriving from the T term are as follows: 1. The longitudinal coupling length is increased by about 5%. 2. The asymmetry parameter σ is altered by a variable but small amount depending on longitudinal gradients in ice thickness h and surface slope α. 3. There is a significant direct modification of the influence of local h and α on flow, which represents a distinct “driving force” in glacier mechanics, whose origin is in pressure gradients linked to stress gradients of the type ∂τxy/∂x. For longitudinal variations in h, the “T force” varies as d2h/dx2 and results in an in-phase enhancement of the flow response to the variations in h, describable (for sinusoidal variations) by a wavelength-dependent enhancement factor. For longitudinal variations in α, the “force” varies as dα/dx and gives a phase-shifted flow response. Although the “T force” is not negligible, its actual effect on τB and on ice flow proves to be small, because it is attenuated by longitudinal stress coupling. The greatest effect is at shortest wavelengths (λ 2.5h), where the flow response to variations in h does not tend to zero as it would otherwise do because of longitudinal coupling, but instead, because of the effect of the “T force”, tends to a response about 4% of what would occur in the absence of longitudinal coupling. If an effect of this small size can be considered negligible, then the influence of the T term can be disregarded. It is then unnecessary to distinguish in glacier mechanics between two length scales for longitudinal averaging of τb, one over which the T term is negligible and one over which it is not.Longitudinal flow-coupling theory also provides a basis for evaluating the additional datum-state effects of the T term on the flow perturbations Δu that result from perturbations Δh and Δα from a datum state with longitudinal stress gradients. Although there are many small effects at the ~1% level, none of them seems to stand out significantly, and at the 10% level all can be neglected.The foregoing conclusions apply for long wavelengths λh. For short wavelengths (λ h), effects of the T term become important in longitudinal coupling, as will be shown in a later paper in this series.

Comparison of void fraction change and local shear stress fluctuation in channel flow

2018 ◽  
Vol 2018 (0) ◽  
pp. OS3-5
Author(s):  
Hayato NAKAMURA ◽  
Satoshi OGAMI ◽  
Yoshihiko OISHI ◽  
Hideki KAWAI ◽  
Yuichi MURAI
Keyword(s):  
Shear Stress ◽  
Channel Flow ◽  
Void Fraction ◽  
Stress Fluctuation ◽  
Local Shear ◽  
Local Shear Stress

scholarly journals The Brachial Artery Remodels to Maintain Local Shear Stress Despite the Presence of Cardiovascular Risk Factors

2009 ◽  
Vol 29 (4) ◽  
pp. 606-612 ◽  
Author(s):  
William B. Chung ◽  
Naomi M. Hamburg ◽  
Monika Holbrook ◽  
Sherene M. Shenouda ◽  
Mustali M. Dohadwala ◽  
...  
Keyword(s):  
Risk Factors ◽  
Shear Stress ◽  
Cardiovascular Risk ◽  
Cardiovascular Risk Factors ◽  
Brachial Artery ◽  
Local Shear ◽  
Local Shear Stress
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