An Examination of the Interaction Between Oil Sand Fragments in Hot Gaseous Streams

1987 ◽  
Vol 109 (2) ◽  
pp. 75-78
Author(s):  
M. A. Abdrabboh ◽  
G. A. Karim
Keyword(s):  
Reynolds Number ◽  
Mass Loss ◽  
Free Stream ◽  
Low Reynolds Number ◽  
Cylindrical Tube ◽  
Stream Temperature ◽  
Oil Sand ◽  
Wide Range ◽  
Single Fragment ◽  
Time Periods

Clusters of preshaped oil sand spherical fragments were subjected to hot steady streams of air at low Reynolds number and constant stream temperature. A wide range of different combinations and arrangements of these fragments were employed involving up to twenty identical spherical samples that were either piled or set normal to the free stream of air and left exposed for various prescribed time periods at constant stream temperatures. The rates of mass loss due to fluid volatilization off these clusters during this exposure were then established experimentally and compared with the corresponding rates derived from the behavior of single spheres. This comparison showed, for the cases considered in this investigation, essentially no significant effect due to the interaction of the spherical samples with each other. The behavior of a single fragment can then form the basis for establishing the volatilization rate of the cluster. However, it was shown that the confinement of these clusters of fragments within a cylindrical tube placed axially along the heating stream produced appreciable effects on the rates of volatilization. The extent of the deviation from the single fragment model observed was then examined and a number of variables affecting it identified.

Development of a Fluids Laboratory Experience in Dimensional Analysis and Similitude Applied to Vortex Shedding From a Cylinder in Cross-Flow

2013 ◽  
Author(s):  
Matthew Anderson ◽  
Dylan Shiltz ◽  
Christopher Damm
Keyword(s):  
Reynolds Number ◽  
Data Acquisition ◽  
Strouhal Number ◽  
Dimensional Analysis ◽  
Vortex Shedding ◽  
Free Stream ◽  
Cross Flow ◽  
Laboratory Experience ◽  
Analysis And Design ◽  
Wide Range

A fluids laboratory experience that introduces students to dimensional analysis and similitude was designed and performed in a junior-level first course in fluid mechanics. After students are given an introduction to dimensional analysis, the technique is applied to the phenomenon of vortex shedding from a cylinder in cross-flow. With help from the instructor, lab groups use dimensional analysis to ascertain the relevant dimensionless pi terms associated with the phenomenon. After successfully determining that the pi terms are the Strouhal number and the Reynolds number, experiments are performed to elucidate the general functional relationship between the dimensionless groups. To conduct the experiments, a wind-tunnel apparatus is used in conjunction with a Pitot tube for measurements of free stream velocity and a platinum-plated tungsten hot-wire anemometer for rapid (up to 400 kHz) measurements of velocity fluctuations downstream of the cylinder. Utilizing an oscilloscope in parallel with a high-speed data acquisition system, students are able to determine the vortex shedding frequency by performing a spectral analysis (via Fourier transform) of the downstream velocity measurements at multiple free stream velocities and for multiple cylinder diameters (thus a varying Reynolds number). The students’ experimental results were found to agree with relationships found in the technical literature, showing a constant Strouhal number of approximately 0.2 over a wide range of Reynolds numbers. This exercise not only gives students valuable experience in dimensional analysis and design of experiments, it also provides exposure to modern data acquisition and analysis methods.

Numerical investigation of the role of free-stream turbulence in boundary-layer separation

2016 ◽  
Vol 801 ◽  
pp. 289-321 ◽  
Author(s):  
Wolfgang Balzer ◽  
H. F. Fasel
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Layer ◽  
Free Stream ◽  
Hydrodynamic Instability ◽  
Low Reynolds Number ◽  
Transition To Turbulence ◽  
Laminar Separation ◽  
Free Stream Turbulence ◽  
Low Reynolds

The aerodynamic performance of lifting surfaces operating at low Reynolds number conditions is impaired by laminar separation. In most cases, transition to turbulence occurs in the separated shear layer as a result of a series of strong hydrodynamic instability mechanisms. Although the understanding of these mechanisms has been significantly advanced over the past decades, key questions remain unanswered about the influence of external factors such as free-stream turbulence (FST) and others on transition and separation. The present study is driven by the need for more accurate predictions of separation and transition phenomena in ‘real world’ applications, where elevated levels of FST can play a significant role (e.g. turbomachinery). Numerical investigations have become an integral part in the effort to enhance our understanding of the intricate interactions between separation and transition. Due to the development of advanced numerical methods and the increase in the performance of supercomputers with parallel architecture, it has become feasible for low Reynolds number application ($O(10^{5})$) to carry out direct numerical simulations (DNS) such that all relevant spatial and temporal scales are resolved without the use of turbulence modelling. Because the employed high-order accurate DNS are characterized by very low levels of background noise, they lend themselves to transition research where the amplification of small disturbances, sometimes even growing from numerical round-off, can be examined in great detail. When comparing results from DNS and experiment, however, it is beneficial, if not necessary, to increase the background disturbance levels in the DNS to levels that are typical for the experiment. For the current work, a numerical model that emulates a realistic free-stream turbulent environment was adapted and implemented into an existing Navier–Stokes code based on a vorticity–velocity formulation. The role FST plays in the transition process was then investigated for a laminar separation bubble forming on a flat plate. FST was shown to cause the formation of the well-known Klebanoff mode that is represented by streamwise-elongated streaks inside the boundary layer. Increasing the FST levels led to accelerated transition, a reduction in bubble size and better agreement with the experiments. Moreover, the stage of linear disturbance growth due to the inviscid shear-layer instability was found to not be ‘bypassed’.

A Finite Element Study of Low Reynolds Number Two-Phase Flow in Cylindrical Tubes

1985 ◽  
Vol 52 (2) ◽  
pp. 253-256 ◽  
Author(s):  
E. I. Shen ◽  
K. S. Udell
Keyword(s):  
Reynolds Number ◽  
Finite Element ◽  
Low Reynolds Number ◽  
Cell Movement ◽  
Cylindrical Tube ◽  
Two Phase ◽  
Bubble Liquid ◽  
Cylindrical Tubes ◽  
Low Reynolds ◽  
Steady State Problem

A finite element solution to the steady-state problem of an inviscid bubble flowing at low Reynolds number in a cylindrical tube occupied by a second viscous phase was obtained. Interfacial tension forces were balanced against the viscous and pressure forces in order to locate the position of bubble-liquid interface. Velocities, pressures, and film thicknesses were obtained as a function of the capillary number. Specific applications of these results include the description of multiphase flow in tubes and porous media, and blood cell movement in small capillaries. The numerical results are compared with published theories and experiments.

The Stability of Water Flow Over Heated and Cooled Flat Plates

1968 ◽  
Vol 90 (1) ◽  
pp. 109-114 ◽  
Author(s):  
Ahmed R. Wazzan ◽  
T. Okamura ◽  
A. M. O. Smith
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Stream Temperature ◽  
Heated Wall ◽  
Flat Plates ◽  
Critical Reynolds Numbers ◽  
The Stability ◽  
Sommerfeld Equation

The theory of two-dimensional instability of laminar flow of water over solid surfaces is extended to include the effects of heat transfer. The equation that governs the stability of these flows to Tollmien-Schlichting disturbances is the Orr-Sommerfeld equation “modified” to include the effect of viscosity variation with temperature. Numerical solutions to this equation at high Reynolds numbers are obtained using a new method of integration. The method makes use of the Gram-Schmidt orthogonalization technique to obtain linearly independent solutions upon numerically integrating the “modified Orr-Sommerfeld” equation using single precision arithmetic. The method leads to satisfactory answers for Reynolds numbers as high as Rδ* = 100,000. The analysis is applied to the case of flow over both heated and cooled flat plates. The results indicate that heating and cooling of the wall have a large influence on the stability of boundary-layer flow in water. At a free-stream temperature of 60 deg F and wall temperatures of 60, 90, 120, 135, 150, 200, and 300deg F, the critical Reynolds numbers Rδ* are 520, 7200, 15200, 15600, 14800, 10250, and 4600, respectively. At a free-stream temperature of 200F and wall temperature of 60 deg F (cooled case), the critical Reynolds number is 151. Therefore, it is evident that a heated wall has a stabilizing effect, whereas a cooled wall has a destabilizing effect. These stability calculations show that heating increases the critical Reynolds number to a maximum value (Rδ* max = 15,700 at a temperature of TW = 130 deg F) but that further heating decreases the critical Reynolds number. In order to determine the influence of the viscosity derivatives upon the results, the critical Reynolds number for the heated case of T∞ = 40 and TW = 130 deg F was determined using (a) the Orr-Sommerfeld equation and (b) the present governing equation. The resulting critical Reynolds numbers are Rδ* = 140,000 and 16,200, respectively. Therefore, it is concluded that the terms pertaining to the first and second derivatives of the viscosity have a considerable destabilizing influence.

Simulating Boundary Layer Transition With Low-Reynolds-Number k–ε Turbulence Models: Part 1—An Evaluation of Prediction Characteristics

1991 ◽  
Vol 113 (1) ◽  
pp. 10-17 ◽  
Author(s):  
R. C. Schmidt ◽  
S. V. Patankar
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Free Stream ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Boundary Layer Transition ◽  
External Boundary ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Low Reynolds

An analysis and evaluation of the capability of k–ε low-Reynolds-number turbulence models to predict transition in external boundary-layer flows subject to free-stream turbulence is presented. The similarities between the near-wall cross-stream regions in a fully turbulent boundary layer and the progressive stages through which developing boundary layers pass in the streamwise direction are used to describe the mechanisms by which the models simulate the transition process. Two representative models (Jones and Launder, 1972; Lam and Bremhorst, 1981) are employed in a series of computational tests designed to answer some specific practical questions about the ability of these models to yield accurate, reliable answers over a range of free-stream turbulence conditions.

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