Measurement of Wall Shearing Stress in the Boundary Layer by Means of an Evaporating Liquid Film

1956 ◽  
Vol 27 (9) ◽  
pp. 1097-1103 ◽  
Author(s):  
James S. Murphy ◽  
A. M. O. Smith
Keyword(s):  
Boundary Layer ◽  
Liquid Film ◽  
Shearing Stress ◽  
Wall Shearing Stress

Errors in static pressure measurements due to protruding pressure taps

1972 ◽  
Vol 54 (3) ◽  
pp. 489-494 ◽  
Author(s):  
H. Zogg ◽  
H. Thomann
Keyword(s):  
Boundary Layer ◽  
Calibration Curve ◽  
Static Pressure ◽  
Pressure Measurements ◽  
Shearing Stress ◽  
Experimental Accuracy ◽  
Probe Diameter ◽  
Wall Shearing Stress

Errors in static pressure measurements caused by taps which protrude beyond the wall and disturb the boundary layer locally are investigated experimentally. The resulting error is presented as a function of the wall shearing stress, the protrusion height and the probe diameter in a representation similar to the calibration curve of Preston tubes. If suitably plotted, the present results can be made to fit this calibration curve to within the experimental accuracy, in spite of the differences between the geometries being compared.

Effect of Transverse Curvature on Turbulent-Boundary-Layer Characteristics

1958 ◽  
Vol 2 (04) ◽  
pp. 33-51
Author(s):  
Yun-Sheng Yu
Keyword(s):  
Boundary Layer ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Pressure Gradient ◽  
Boundary Layer Thickness ◽  
Axial Flow ◽  
Shearing Stress ◽  
Transverse Curvature ◽  
Similarity Laws

Tests made on the turbulent boundary layer on a circular cylinder in axial flow at zero pressure gradient are described. From the measurements, similarity laws of the velocity profile are formulated, and various boundary-layer characteristics are evaluated and compared with the flatplate results. It is found that the effect of transverse curvature is to increase the surface shearing stress and to decrease the boundary-layer thickness, and that the latter variation is more pronounced than the former.

Some Experiments on the Reattachment of a Laminar Boundary Layer Separating From a Rearward Facing Step on a Flat Plate Aerofoil

1960 ◽  
Vol 64 (599) ◽  
pp. 668-672 ◽  
Author(s):  
T. W. F. Moore
Keyword(s):  
Boundary Layer ◽  
Liquid Film ◽  
Flat Plate ◽  
Laminar Boundary Layer ◽  
Reverse Flow ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Pressure Measurements ◽  
Flow Vortex

Summary:The results of experiments on the reattachment of a laminar boundary layer, separating from a rearward facing step in a flat plate aerofoil, are correlated with the properties of the short leading edge bubble which forms on thin aerofoils near the stall.The experiments, comprising pressure measurements, Pitot explorations, liquid film and smoke studies, indicate that for all Reynolds numbers above the value given by the Owen-KIanfer criterion the reattachment is turbulent behind a stationary air reverse flow vortex bubble. It is also found that the reattachment is laminar for Reynolds numbers below the critical, which further supports Crabtree's interpretation of the Owen-KIanfer criterion in terms of the condition for the growth of turbulent bursts.

Features of a separating turbulent boundary layer in the vicinity of separation

1977 ◽  
Vol 79 (3) ◽  
pp. 553-594 ◽  
Author(s):  
Roger L. Simpson ◽  
J. H. Strickland ◽  
P. W. Barr
Keyword(s):  
Boundary Layer ◽  
Outer Region ◽  
Turbulence Energy ◽  
Shearing Stress ◽  
Low Velocity ◽  
Laser Anemometer ◽  
Apparent Similarity ◽  
Energy Equations ◽  
Anemometer System ◽  
Hot Film

Measurements of a separating two-dimensional incompressible boundary layer with an airfoil-type pressure distribution are reported. Unique mean and fluctuation velocity measurements and the distribution of the fraction of the time γp during which the flow moves downstream were obtained in the separated region using a directionally sensitive laser anemometer. Linearized hot-film anemometer measurements of mean velocities, turbulent shearing stress and intensities, eddy speeds, spectra and dissipation were made for γp > 0·8. The wall shearing stress, bursting frequencies, wall speed and spanwise structure were obtained using flush-surface hot-film sensors. The turbulent/non-turbulent interfacial intermittency γ and the frequency of passage of turbulent bulges were determined using smoke as a turbulence marker and the laser anemometer system for illumination and signal detection.Upstream of separation the velocity profile correlations of Perry & Schofield (1973) are supported within the uncertainty of the data. Normal-stress effects are very important, influencing $-\overline{uv}/\overline{q^2} $ and the dissipation length correlations, and directly providing sizable terms in the momentum and turbulence energy equations. The criteria of Sandborn for turbulent separation and fully developed separation are found to hold. Downstream of separation there is apparent similarity of $\overline{u^2}$, U and γp throughout the shear flow. The passive low velocity backflow near the wall apparently just serves to satisfy continuity requirements after the energetic outer-region flow has deflected away from the wall upon separation.The wall bursting frequency nA scales on outer velocity and length scales, with U∞/δnA ≈ 10, or about twice the value observed for zero-pressure-gradient flows. The non-dimensional spanwise spacing of wall eddies is given approximately by the relation λzUM/v ≈ 100 upstream of separation, where $U_M = (- \overline{uv}_{\max})^{\frac{1}{2}}$. The speed of wall eddies is found to be about 14Uτ.

Boundary Layer Mechanism of a Two-Phase Nanofluid Subject to Coupled Interface Dynamics of Fluid/Film

2019 ◽  
Vol 75 (1) ◽  
pp. 43-53
Author(s):  
Shengna Liu ◽  
Xiaochuan Liu ◽  
Liancun Zheng
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Brownian Motion ◽  
Liquid Film ◽  
Rheological Properties ◽  
Thin Liquid Film ◽  
Velocity Ratio ◽  
Linear Functions ◽  
Two Phase ◽  
Interface Dynamics

AbstractThis article investigates boundary layer mechanism of a two-phase nanofluid over a thin liquid film of power-law fluid. We take the coupled interface dynamics between the thin liquid film and nanofluid into consideration, where the thermal conductivity and dynamic viscosity are assumed to be linear functions of nanoparticle concentration. The influence of Brownian motion and thermophoresis of the nanofluid is also considered. Numerical results are carried out by employing similarity transformation and bvp4c technique. The heat and mass transfer in the flow boundary layer are analysed by relevant parameters with the assistance of graphs. The results show that heat conduction decreases significantly with the increase of rheological properties parameter and tensile velocity ratio. Rheological properties parameter, tensile velocity ratio, Brownian motion parameter and thermophoresis parameter play important roles in mass transfer.

Analysis of Passive Tube Condensation With Non-Condensable Gas Using Heat and Mass Analogy Model

2021 ◽  
Author(s):  
Ugur Cotul ◽  
Shripad T. Revankar
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Condensation Heat Transfer ◽  
Vapor Flow ◽  
Vapor Mixture ◽  
Condenser Tube ◽  
Numerical Predictions

Abstract In this study, we used the heat and mass analogy model to be able to predict the heat transfer properties of a condenser tube operating in passive mode. The most important advantage of analogy model comparing boundary layer model is simplicity and fast computation, that’s why it can be applied to various engineering problems for many cases. The heat and mass analogy model is based on the heat transfer balance between liquid film and gas mixture area. The main problem for the liquid film region is the heat transfer coefficient (HTC) which is affected negatively in the presence of non-condensable gas. Therefore, our main goal is to increase the HTC and condensation heat transfer rate by updating the analogy code. In the gas-vapor mixture region, heat transfer mainly occurred as latent condensation and sensible heat transfer. In order to maintain this balance between the mixture and liquid film, the interface temperature is iterated. After defining a specified tolerance value of the heat and mass analogy model codes, this iteration process was started to be used at the entrance of a condenser tube. The gas and vapor mixture is considered to be saturated at the liquid/gas interface in the heat and mass transfer analogy model. Via boundary layer study of species concentration and energy balance, the non-condensable gas effect on condensation is added into the equation. For the condensation heat transfer coefficient of turbulent vapor flow associated with laminar condensate, numerical predictions were made and they were satisfactory. The predictions were compared with the experimental data from the literature to be able to test the model. Non-condensable gas mass fraction and vapor-non-condensable mixture temperature were presented in the form of radial and axial profiles.

Short- to long-wave resonance and soliton formation in boundary-layer interaction with a liquid film

2010 ◽  
Vol 660 ◽  
pp. 162-196 ◽  
Author(s):  
M. VLACHOMITROU ◽  
N. PELEKASIS
Keyword(s):  
Boundary Layer ◽  
Liquid Film ◽  
Numerical Simulations ◽  
Separation Bubble ◽  
Capillary Waves ◽  
Base Flow ◽  
Long Waves ◽  
Linear Wave ◽  
Interfacial Waves ◽  
Supercritical Regime

Dynamic interaction between a boundary layer of air and a liquid film is investigated in this paper. The low air-to-film-viscosity ratio is considered in which case the boundary layer is quasi-steady on the time scale within which interfacial waves develop. The base flow consists of a boundary layer that drags a film of constant shear. Linear analysis, in the context of triple-deck theory, predicts the formation of a wavepacket of capillary waves that advances and spreads with time. The Froude number of de-/anti-icing fluids or water interacting with air falls well within the supercritical regime, i.e. Fr > FrCr. Numerical simulations of such flow systems were performed in the context of triple-deck theory, and they do not exhibit wave saturation or formation of uniform wavetrains. The long-term interaction is mainly dependent on film inertia as this is characterized by parameter = (μ/μf)2(ρf/ρ), which involves film and air viscosity and density ratios, and the dimensionless film thickness, H0, and shear, λ, provided by the base flow. Weakly nonlinear analysis taking into consideration mean drift, i.e. generation of long waves, due to self-interaction of the linear wave to O(ϵ2) in amplitude of the initial disturbance, reveals resonance between the wavepacket predicted by linear theory and long waves when the group velocity of the former happens to coincide with the phase velocity, H0λ, of long interfacial waves. Numerical simulations with anti-icing fluids and water verify this pattern. In both cases, long waves eventually dominate the dynamics and, as they are modulated with time, they lead to soliton-type structures. Anti-icing fluids eventually exhibit oscillatory spikes whose mean value never exceeds 2H0, roughly. Water films exhibit a single spike that keeps growing, thus generating a large separation bubble.

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