Boundary Layer Theory

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Analytical Study On Flow Through a Pelton Turbine Bucket Using Boundary Layer Theory

Analytical Study On Flow Through a Pelton Turbine Bucket Using Boundary Layer Theory

Abstract-- Elementary mathematical formulas governing the power developed by the Pelton turbine and design were deduced in early 1883. At that time the principal sources of loss are identified as the energy remaining in water after being discharged from the bucket, The heat developed by impact of water in striking the bucket, The fluid friction of the water in passing over the surface of the bucket, The loss of head in the nozzle, The journal friction the resistance of the air. It was assumed that the effect from of above all the losses were negligible when deriving the Mathematical formula governing the performance of the Pelton wheels. And also it was assumed that the all the water escapes from the bucket with the same velocity. Among the various analytical studies that had been done on Pelton turbine hydraulics l ess attention has been paid to the friction along the buckets . In this paper the effect of bucket friction was analyzed using Boundary Layer theory.
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Flow Characteristics in Riffles by Using   Boundary-layer Theory

Flow Characteristics in Riffles by Using Boundary-layer Theory

which the distributions of velocity and turbulence components are also shaped. In the boundary layer theory, the flow in open channels can be distinguished into two regions-inner and outer. In the inner region, which is limited to z h < 0.2 in uniform flow, the velocity profile can be expressed by the wall law as equation (1). The wall law states that the average velocity of a turbulent stream is proportional to a logarithmic distance from that point to the wall. This law was considered by von Karman (1930), which particularly applies to a portion of the current near the bed (less than 20% of the depth of the stream).
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Two parameter integral methods in laminar boundary layer theory

Two parameter integral methods in laminar boundary layer theory

The work of this thesis is concerned with the investigation and attempted improvement of an integral method for solving the two dimensional, incompressible laminar boundary layer equations of fluid dynamics. The method which, is based on a theoretical two parameter representation of well known boundary layer properties was first produced by Professor S. N. Curie. Its range of appli­ cation, reliability and accuracy rely on four universal functions which have been derived from known exact solutions to the boundary layer equations, and are given tabulated in terms of a pressure
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Boundary layer over a flat plate

Boundary layer over a flat plate

We have described the continuity and Navier-Stokes equations. These are the starting point of Prandtl’s boundary-layer theory. We will describe steady, incompressible flow. Steady means that the flow at a particular position in space will not change in time. In other words, when taking a picture of for example the flow field around a car (imagine the flow would be visible), the picture will look the same at time and time , for arbitrary . Incompressible flow means it is not possible to change the density of air. Also we assume to have a 2-dimensional flow within the (x,y) plane. And the last assumption is neglecting the effect of gravity, which will have little influence on the flow inside the boundary layer.
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Induced dusty flow due to normal oscillation of wavy wall

Induced dusty flow due to normal oscillation of wavy wall

Abstract. A two-dimensional viscous dusty flow induced by normal oscillation of a wavy wall for moderately large Reynolds number is studied on the basis of boundary layer theory in the case where the thickness of the boundary layer is larger than the amplitude of the wavy wall. Solutions are obtained in terms of a series expansion with respect to small amplitude by a regular perturbation method. Graphs of velocity components, both for outer flowand inner flowfor various values of mass concentration of dust particles are drawn. The inner and outer solutions are matched by the matching process. An interested application of present result to mechanical engineering may be the possibility of the fluid and dust transportation without an external pressure.
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Speculation in Science and Technology: Is the Quantum Wave Nothing More than a Prandtl Boundary Layer?

Speculation in Science and Technology: Is the Quantum Wave Nothing More than a Prandtl Boundary Layer?

Consequently the aim of the present note is to suggest at a minimum a likeness or analogy between the fundamental discovery of Prandtl’s boundary layer theory [13-15], which revolutionized fluid dynamics and thus aircraft, ships and submarine design [13-20] on one hand and on the other hand relates it all to the meaning and physics behind the highly controversial quantum wave collapse, i.e. state vector reduction of quantum mechanics [21-22] that formed a substantial part of the work and legacy of David Bohm [5-7]. Ultimately Bohm had to escape from the witch-hunt of the McCarthy ear in the USA to the freedom of science and belief in Birkbeck College in England, the promise land in that time [5-7].
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Frictional convergence, atmospheric convection, and causality

Frictional convergence, atmospheric convection, and causality

Charney and Eliassen (1964) argued in essence that the depth of the free tropospheric secondary circulation associated with cross-isobaric frictional flow is comparable to the depth of the troposphere. As noted in section 1, the steady-state approximation would be valid if this were true, and the vertical motion at the top of the boundary layer could be said to be caused by the action of surface friction. However, as we have shown, typical values of atmospheric stratification result in a far shallower secondary circulation in response to surface friction. Under these circumstances, the time tendency of the wind along the isobars cannot be neglected for a flow of any reasonable horizontal scale (say < 1000 km) in the tropics. For horizontal scales of order 100 km or less, the vertical scale of the secondary circulation is typically much smaller than the thickness of the layer over which surface friction is deposited, especially when there is widespread shallow, moist convection such as occurs in the trade wind regions. In this situation there is essentially no cross-isobaric transport in a boundary layer spinning down under the influence of friction. If some mechanism external to boundary layer dynamics (such as mass sources imposed by deep convection) acts to maintain the boundary layer flow in a nearly steady state, then the time tendency of the boundary layer wind along the isobars becomes small or zero and cross-isobaric flow and resulting convergence exists more or less in the amount predicted by steady-state boundary layer theory. However, the immediate cause of this convergence and the resulting vertical motion at the top of the boundary layer is actually the convection itself, and not boundary layer dynamics; surface friction could be completely absent and the convergence would still exist if the convection were still present.
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Effect of Modeling Hypersonic Flow Physics on Electro Optical Sensor Assessment

Effect of Modeling Hypersonic Flow Physics on Electro Optical Sensor Assessment

The results for the optical calculations for the range of data from x = 0.23 m to x = 0.25 m are shown in Fig. 12. Since it is the variations in flow that distort optical calculations, it is unsurprising that the ILES shows the largest OPDs. This can be attributed to the fact that the ILES simulation is the only one that captures fluctuating quantities. While the Menter SST simulation produces a similar boundary layer thicknesses and bulk flow quantities, it is unable to provide fluctuating values, and because of this the OPD profile of this region is not significantly dissimilar to the OPD profile of the laminar solution; both produce tilted linear OPDs that are up to two orders of magnitude lower than the non-linear OPDs predicted from the ILES simulation.
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Convection and Chemistry in the Atmospheric Boundary Layer

Convection and Chemistry in the Atmospheric Boundary Layer

From a range of possible topics indicated in the original project proposal the turbulent transport–reaction problem in the atmospheric boundary layer was chosen as the primary focus of my research. This choice was to some extent coincidental but to a large extent the result of the presence of a research program on this topic at Utrecht University (involving Peter Builtjes, Jordi Vil`a-Guerau de Arellano, Peter Duynkerke, Kees Beets, Han van Dop, Stefano Galmarini, Lianne Crone, Maarten Krol, and Laurens Ganzeveld) and the Royal Netherlands Meteorological Institute (KNMI; involving G´e Verver). These colleagues were all studying specific aspects of the turbulent transport–reaction problem and some had put forth evidence that current large-scale atmospheric chemistry models are in error due to some simplifying assumptions contained in these models. However, the precise contribu- tion of the neglected aspects of the turbulent transport–reaction problem to inaccuracies in the models was still unknown, since no simple “parameterizations” of these effects were available for inclusion in the models. Thus the aim of my studies became the develop- ment of a simple parameterization for one aspect (“segregation effects”) of the mentioned problem.
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On hairpin vortices in a transitional boundary layer

On hairpin vortices in a transitional boundary layer

The transition from laminar to turbulent flow is of great practical interest. The final phase of laminar boundary layer transition starts always with the occurrence of first turbulent spots. Emmons [1] first reported the turbulent spots or simply spots as isolated regions of strong fluctuations that are streamwise carried, growing in size and coalescing with neighbours within the transitional boundary layer. The hairpin vortices and packets of hairpin vortices are typical structures within turbulent spots. Spots appear irregularly in time and at arbitrary location of the boundary layer and they are considered to be the building blocks of boundary layer turbulence, they control the length of the transition region etc. – see e.g. Narasimha [2]. The turbulent spots followed by calmed regions are defined structures that dominate the last stage of transition. Spots production affects the length of transition region. The turbulent spots creation rate, growth characteristics and their merger lead to fully developed turbulent flow. A brief summary on turbulent spot and calmed region was compiled in Jonáš [3].
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Vol 3, No 5 (2012)

Vol 3, No 5 (2012)

Boundary layer flow on continuous moving surface is an important type of flow occurring in a number of engineering processes. Aerodynamic extrusion of plastic sheets, cooling of an infinite metallic plate in a cooling path, the boundary layer along a liquid film in condensation process and a polymer sheet of filament extruded continuously from a die are examples of practical applications of continuous moving surfaces. Gas blowing, continuous casting and spinning of fibers also involve the flow due to a stretching surface.

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Retrieval of tropospheric NO 2using the MAX-DOAS method combined with relative intensity measurements for aerosol correction

Retrieval of tropospheric NO 2using the MAX-DOAS method combined with relative intensity measurements for aerosol correction

Table 1. Sensitivity study of eight parameters affecting tropospheric NO 2 retrieval: AOT, boundary layer height for NO 2 and aerosols (BLH), boundary layer column of NO 2 (N), asymmetry parameter of aerosols (ASY), single scattering albedo of aerosols (SSA), surface albedo (ALB), and polarization (POL). Each parameter was changed in the DAK model from case 1 (reference value) to case 2, with all other parameters unchanged. For the elevations 4 ◦ , 8 ◦ and 16 ◦ , the effect of this change is given in percent for the relative intensity (I rel ), the differential air mass factor (1M), and for the tropospheric NO 2 column retrieved by the two-step algorithm (N Tr ). The percentage was calculated as follows: [P (case 1)–P (case 2)]/P (case 2) × 100%, where, for each line, P (case 2) is the model simulation where only the quantity indicated by the first column of that line was changed to case 2, and where all other parameters were as in case 1. The values in the table therefore represent the error made when the ‘true’ atmosphere would be in a state with one specific parameter as in case 2, whereas this and all other parameters are assumed to be as in case 1 (which corresponds to the settings of the look-up tables described in Sect. 3.1.2). Values were calculated for a solar zenith angle of 60 ◦ and a relative azimuth of 180 ◦ .
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Boundary Layer Method for Unsteady Transonic Flow

Boundary Layer Method for Unsteady Transonic Flow

boundary layer, which are functions of distance from the stagnation point along the airfoil contour. These distributions are the output of the inviscid part of flow, taken at the position of the airfoil contour. The computational grid for boundary layer calculations was one-dimensional with the same number of main nodes as that of control volumes in the inviscid solver bounding the airfoil contour. Between these main nodes, integration was performed on twenty subintervals. The integration of the boundary layer equations starts from the initial solution for the flat plate in laminar flow. The boundary layer initial solution was obtained from the Blasius solution [23] and [24].
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Experimental and computational investigation of flow
about low aspect ratio ellipsoids at transcritical
Reynolds numbers

Experimental and computational investigation of flow about low aspect ratio ellipsoids at transcritical Reynolds numbers

Hot films may be placed on the model surface [17], or pressure sensors may be placed flush with the surface or behind pinhole tappings, in order to measure the fluctuations due to turbu- lence [81]. These two methods have the advantage that they are essentially non-intrusive and allow simultaneous measurements. A disadvantage is that they do not give useful information in regions of separated flow. Each measurement point requires its own transducer and signal conditioning equipment. Hot wire, hot film and pressure probes may be traversed along the surface. These techniques allow for a high density of measurement points. However there are errors associated with the intrusive nature of a physical probe. Regardless of the sensor, a procedure is required to discriminate between periods of laminar and turbulent flow. Hedley and Keffer [82], together with Canepa [83], provide reviews on a number of these techniques. These methods provide the instantaneous intermittency, , which has a value of 1 when the boundary layer is turbulent and 0 when laminar. The time averaged intermittency, N , is given by
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Thermal Ignition Using Moving Hot Particles

Thermal Ignition Using Moving Hot Particles

it was purely a study on understanding the effect of activation energy, wall boundary condition, and wall temperature on ignition. Sano and Yamashita (1994) performed thorough two-dimensional simulations of ignition in a methane-air laminar boundary layer over a horizontal hot plate. The reaction mechanism for methane-air consisted of 18 species and 61 elementary reactions. The plate consisted of a hot section placed between two cold sections. The study focused on the effects of wall temperature, flow velocity, hot plate length, and species boundary condition at the wall, i.e. (a) species concentration vanishing at the wall (reactive) and (b) zero species diffusion to the wall (inert), on ignition. Sano and Yamashita (1994) used an ignition criterion based on the peak of the methane consumption rate to determine an ignition delay time. Changing the flow velocity from 1 to 100 cm/s did not affect the ignition delay time since ignition occurred close to the wall. In addition, they found that decreasing the hot surface length led to an exponential increase in the delay time whereas increasing the length resulted in a constant delay time. Finally, to test the effect of a reactive wall, several species mass fractions were set to zero at the wall, e.g. H, O, OH, HO 2 ,
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The Boundary layer over a flat plate

The Boundary layer over a flat plate

The results of the drag force measurements are shown below. Information about the load cell, which was used to determine the drag force, can be found in Appendix C.4. The results show transition at a quite high Reynolds number, which is not as expected. According to the theory and XFOIL simulations, the critical Reynolds number at which transition should occur is at approximately 500,000 whereas in the present experiment transition occurs at a Reynolds number of about 3,000,0000. A possible cause is the streamwise pressure gradient for which the results are represented in section 13.4. The measured drag coefficient for laminar flow is observed to be slightly higher than the value from theory, which is most likely caused by the interaction of the side walls of the wind tunnel with the boundary layer on the plate.
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The Effect of Curvature on Boundary Layer Transition

The Effect of Curvature on Boundary Layer Transition

section we.re 0om:pleted oz:i tra?1si tion blil.. front or th$ sheEtt*e leading.[r]

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The Theory and Experimental Study of the Self Excited Oscillation Pulsed Jet Nozzle (Pipeline Pulsed Flow Generator)

The Theory and Experimental Study of the Self Excited Oscillation Pulsed Jet Nozzle (Pipeline Pulsed Flow Generator)

From Figures 10, 11, some conclusions can be drawn: 1) The pressure of jet is influenced by some factors in- cluding the rate of L/d (L represents the length of cavity, d represents the diameter of upstream nozzle), the rate of diameters of upstream nozzle and the diameter of down- stream nozzle, the shape of impinging edge, the shape of cavity, etc.. If the rate of L/d is too small, it is very dif- ficult to form a stable shearing layer. But if the rate of L/d is too large, the disturbance waves reflected can not induce the generation of new vortex waves. So, choosing suitable rate of L/d is very important. In addition, the shape of impinging edge and the shape of cavity will influence the peak of pressure of jet.
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Wave boundary layer streaming: analysis on wave boundary layer streaming and its effect on bed shear stress

Wave boundary layer streaming: analysis on wave boundary layer streaming and its effect on bed shear stress

PSM DV99 original DV99 adjusted Free-stream velocity... vRijn without streaming..[r]

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Numerical Simulation of Vortex Street Around the Two Dimensional Cylinder Based on LES

Numerical Simulation of Vortex Street Around the Two Dimensional Cylinder Based on LES

Figure 5 selects the contour maps of the velocity at six representative moments when the velocity of the flow field is 2 m/s. The figure shows the formation and dissipation of a vortex street. At t = 0 s, the velocity of the flow field has not yet played a role, and vortices have not yet formed. At t = 2 s, a vortex is being formed, and two vortices with different velocity distributions are formed, one with a high speed is outside the boundary layer, and one with a low speed is inside the boundary layer. At t = 4 s, the left and right sides of the two-dimensional cylinder alternately form mature vortices, and a vortex street is formed after the two-dimensional cylinder. At t = 6 s, the initially formed vortex is moving forward and has reached the entrance boundary. At t = 8 s, the vortex with a small velocity starts to dissipate after a certain distance.
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