Showing papers on "Pipe flow published in 1969"

Rough wall turbulent boundary layers

Abstract: This paper describes a detailed experimental study of turbulent boundary-layer development over rough walls in both zero and adverse pressure gradients. In contrast to previous work on this problem the skin friction was determined by pressure tapping the roughness elements and measuring their form drag.Two wall roughness geometries were chosen each giving a different law of behaviour; they were selected on the basis of their reported behaviour in pipe flow experiments. One type gives a Clauser type roughness function which depends on a Reynolds number based on the shear velocity and on a length associated with the size of the roughness. The other type of roughness (typified by a smooth wall containing a pattern of narrow cavities) has been tested in pipes and it is shown here that these pipe results indicate that the corresponding roughness function does not depend on roughness scale but depends instead on the pipe diameter. In boundary-layer flow the first type of roughness gives a roughness function identical to pipe flow as given by Clauser and verified by Hama and Perry & Joubert. The emphasis of this work is on the second type of roughness in boundary-layer flow. No external length scale associated with the boundary layer that is analogous to pipe diameter has been found, except perhaps for the zero pressure gradient case. However, it has been found that results for both types of roughness correlate with a Reynolds number based on the wall shear velocity and on the distance below the crests of the elements from where the logarithmic distribution of velocity is measured. One important implication of this is that a zero pressure gradient boundary layer with a cavity type rough wall conforms to Rotta's condition of precise self preserving flow. Some other implications of this are also discussed.

On the instability of viscous flow in a rapidly rotating pipe

Abstract: The stability of almost fully developed viscous flow in a rotating pipe is considered. In cylindrical polar co-ordinates (r, o, z) this flow has the velocity components \[ \{W_0o(1),\quad\Omega r[1+o(\epsilon)],\quad W_0[1-r^2/r^2_0+o(1)]\},_{+}^{+} \] where e = Wo/2Ωr0 and is bounded externally by the rigid cylinder r = r0, which rotates about its axis with angular velocity Ω. In the limit of small e, the disturbance equations can be solved in terms of Bessel functions and it is shown that, in that limit, the flow is unstable for Reynolds numbers R = Wor0/v greater than Rc [asymp ] 82[sdot ]9. The unstable disturbances take the form of growing spiral waves, which are stationary relative to the rotating cylinder and the critical disturbance at R = Rc has azimuthal wave-number 1 and axial wavelength 2πr0/e. Furthermore, it is shown that the most rapidly growing disturbance for R > Rc has an azimuthal wave-number which increases with R. Some of the problems involved in testing the results by experiment are discussed and a possible application to the theory of vortex breakdown is mentioned. In an appendix this instability is shown to be an example of inertial instability.

Slip flow through long circular tubes

Abstract: Slip flow of nitrogen gas through long circular tubes, measuring mass flow, pressure drop and cross sectional velocity profiles

Separation and flow reversal in swirling flows in circular ducts.

Abstract: The swirling motion of a laminar incompressible viscous flow in a circular duct is studied. The duct consists of two smoothly joined sections, one stationary and the other rotating with a constant angular velocity. A linearized analytical solution, valid for flows having small Reynolds numbers and large swirl ratios, is developed. Solutions for a wider range of Reynolds numbers and swirl ratios are obtained by numerically solving the discretized angular momentum and vorticity transport equations. The occurrence of flow reversal on the axis and near the tube wall is studied, in particular, and conditions for incipient flow reversal are established.

Pipe flow of suspensions

Abstract: This study shows that fully developed pipe flow of a particulate suspension is defined by four dimensionless parameters of particle-fluid interactions in addition to the Reynolds number Effects accounted for include the Magnus effect due to fluid shear, electrostatic repulsion due to electric charges on the particles, and Brownian or turbulent diffusion In the case of a laminar liquid-solid suspension, electrostatic effect is negligible but shear effect is prominent Solution of the basic equations gives the density distribution of particles with a peak at the center (Einstein, Jeffery) or at other radii between the center and the pipe wall (Segre et al) depending on the magnitudes of the various flow parameters In the case of a turbulent gas-solid suspension, the Magnus effect is significant only within the thickness of the laminar sublayer However, charges induced on the particles by the impact of particles at the wall produce a higher density at the wall than at the center of the pipe The velocity distribution of particles is characterized by a slip velocity at the wall and a lag in velocity in the core from the fluid phase These results are verified by earlier measurements

Control of Transient Free - Surface Flow

Abstract: A theory is presented to define methods of optimum gate operation for altering flow conditions in an open channel. The analytical procedure prescribes the motion of the control devices in the channel so the transient conditions are known and controlled during the period when the flow is being changed from one given situation to another desired flow condition. The method is applicable to cases of initiating flow, increasing flow, decreasing flow, or stopping flow in irrigation channels, power channels, forebay channels to pumping stations, etc. The theory is developed from the basic differential equations for unsteady flow in a prismatic channel, including frictional losses. Two examples are detailed in this study.

Thermal Entry for Low Reynolds Number Turbulent Flow

Abstract: Thermal entry problem solution for low Reynolds number turbulent gas flow based on Reynolds number dependent velocity profile

Propagation Velocity of Turbulent Slugs and Streaks in Transition Pipe Flow

Abstract: Taking account of experimental observations on the transition process, an elementary theory is developed for estimation of propagation velocity of the rear end of turbulent slugs and streaks which constitute a major feature of the transition process in pipe flow. The theory gives a lower propagation velocity than observed experimentally within the lower range of transition Reynolds numbers while at higher Reynolds numbers the theory gives a value about 7% higher than obtained experimentally. These deviations are due to approximations in the analysis which cannot be avoided at the present level of information on the structure of turbulent shear.

A Simplified Statistical Model of Turbulent, Chemically Reacting Shear Flows

Abstract: A turbulence theory has been formulated which describes, in a simplified, tractable manner, the effect of various wavenumber fluctuations on the statistical behavior of the fluid elements containing reactive species. The theory was then employed, as a primary test, to analyze the turbulent Couette flow of a chemically inert fluid. In the analysis, it was shown that the present theory as applied to a chemically inert fluid is self-containi ng up to the dissipation function. An experimental value of dissipation function for a pipe flow, for lack of the same for a Couette flow, was adapted and used in the analysis. A comparison of the present theoretical results with the available experimental data on Couette flow showed a satisfactory agreement between the two. A simple relationship has been derived between the dissipation function and the other variables of the theory which would render the present theory completely self-containing for the chemically inert single-component flow.

Mass flow rate for nearly-free molecular slit flow

Abstract: Mass flow rates for nearly free molecular flow through two dimensional slit for several tank pressure ratios

The Onset of Dilute Polymer Solution Phenomena

Abstract: It is shown that in dilute polymer solution flows anomalous behaviour begins — onsets — abruptly. The experimental evidence concerning onset in turbulent pipe flow is reviewed and the observed effects of flow and polymeric parameters summarized. Theoretical approaches to pipe flow onset are analysed and three types of onset hypotheses are evaluated against experimental data. A semi-empirical correlation is presented for onset in pipes. Onset results are used to derive the ratios of macromolecular/eddy length and time scales. The possible influence of steric factors is noted.

Turbulent and transition pipe flow of dilute aqueous polymer solutions

Abstract: The addition of minute quantities of high molecular weight polymers to water can produce a large reduction in the turbulent pipe flow friction. A laser-Doppler instrument for measuring local velocity is used to study transition and turbulent pipe flow of a 50-WPPM aqueous solution of Polyox WSR 301 (polyethylene oxide) at the center of a 14-mm diam pipe. The addition of the polymer to water does not significantly alter the level of the longitudinal turbulence intensity at the center line over the range of Reynolds numbers studied. A surprising result of polymer addition occurs below a Reynolds number of 2,500 in the region of the hump. The increased relative band widths of the frequency spectra in this region imply an uncertainty in the fluid velocity. This result, together with the observed concurrent decrease in the ratio of center line to bulk velocity relative to pure water, shows that the flow is no longer of the steady Poiseuille type after the addition of Polyox WSR 301. The absence of spikes from the frequency spectra further implies that the flow is not intermittent in the sense that laminar and turbulent slugs are alternately passing the point of measurement. At these Reynolds numbers,more » the flow is probably laminar but unsteady. (18 refs.)« less

Study on Flow Characteristics in Right-Angled Pipe Fittings : 1st Report, On Case of Water Flow

Abstract: The flow characteristics of water through right-angled pipe fittings were studied by theoretical and experimental method. By means of the theory of two-dimensional potential flow, streamlines and pressure distributions along the walls of right-angled branching canals, in which the flow separated at the branch corner, were evaluated and compared with the experimental results. Both results coincided very well. From the calculated and experimental results, the mechanisms of the pressure loss of right-angled pipe fittings were analyzed. The pressure loss in the main flow was equivalent to the pressure loss of a sudden enlargement and that in the branch flow to the sum of the pressure loss of a sudden contraction and a sudden enlargement.

Effect of Polymer Additive on Grid Turbulence

Abstract: ALTHOUGH many detailed investigations have been made of the drag reduction in pipe flow caused by polymer additives, very little quantitative information is available about the effect of polymers on grid turbulence. This is known to be small in the absence of the high shear stresses associated with boundary layer flow, but photographs show that there is a definite suppression of eddies in the high frequencies1–3. Hot film probes have been used in the past to study polymer flow in pipes4 but were not used in these investigations because their accuracy is known to be poor in non-Newtonian fluids. Instead, a laser velocimeter was constructed with a signal analysing system that gave a voltage output proportional to the instantaneous axial velocity, and could be used to determine both root mean square (r.m.s.) turbulent intensities and power spectral densities. Full details of the optical arrangement and electrical circuits are given in ref. 5.

Some Observations on the Flow Characteristics of Certain Dilute Macromolecular Solutions

Abstract: The flow characteristics of some dilute macromolecular solutions have been studied in a number of systems, including smooth pipes, rough pipes, submerged jets, flow around spheres, and wall-attachment experiments.

Surging in Laboratory Pipeline with Steady Inflow

Abstract: Surges of head and discharge were studied experimentally in a laboratory pipeline which had check structures spaced at equal distances along the pipe. Surges developed when the downstream portion of the check structures did not flow full. The surges were initiated by the release of air entrained in the downstream leg of the check structures, and the surges were amplified as the flow passed through the successive pipe reaches. The experiments were made for various inflows which were steady at the upstream end of the pipe. Plots of surge magnitude vs. inflow rate show two peaks. One peak apparently corresponds to surges initiated by air release through the vent downstream of the check structures; the other peak, to surges initiated by air release through the downstream part of the check structure. The nonlinear momentum equation was integrated numerically to predict the growth of the discharge surge from one pipe reach to the next. The general character of the results is presented. The results were in good agreement with the experiments.

Apparatus for separating and measuring gas in drilling fluid

Abstract: Apparatus is provided for use in wells, allowing the well to be drilled with minimum hydrostatic head and yet insuring against the possibility of blowouts, and for measuring the gas flow rate from a separator which includes a plurality of parallel pipes of differing sizes. Each pipe has a flow rate detector, and suitable valves are included for passing the gas flow into whichever pipe is desired, depending on the flow rate. If the flow rate is great, a large pipe is used; if the flow rate is small, a small pipe is used.

Dynamics of Compressible Saturated Two-Phase Flow : Critical Flow-sequel, and Flow in a Pipe

Abstract: Improving the analysis of the author's previous report on a few points of importance, an exact analysis based on fundamental laws of dynamics and thermodynamics is accomplished on a simple but clearly defined model of compressible saturated two-phase flow As the result, fundamental matters such as the behavior of energy within the two phases, the change of phase, the change of entropy, the variation of pressure near the exit of pipe in critical flow and others are clarified with physical distinctness Besides, numerical computation is carried out for critical flow of the model afore-mentioned in case of water / steam system, and the results are presented Distinction between critical flow with evaporation and that with condensation has an important effect on the analysis

Dynamic response of a Mach 2.5 axisymmetric inlet with engine or cold pipe and utilizing 60 percent supersonic internal area contraction

Abstract: Dynamic response of supersonic mixed compression inlet coupled to cold pipe or turbojet engine

Analysis of suddenly started laminar flow in the entrance region of a circular tube

Abstract: Suddenly started laminar flow in the entrance region of a circular tube, with constant inlet velocity, is investigated analytically by using integral momentum approach. A closed form solution to the integral momentum equation is obtained by the method of characteristics to determine boundary layer thickness, entrance length, velocity profile, and pressure gradient.

Transition from film to nucleate boiling in vertical forced flow.

Abstract: Film-nucleate boiling transition for liquid nitrogen in vertical forced flow in electrically heated tube, discussing conduction model and agreement with visual experiment

Fluid flow rate actuated change over valve

Abstract: A fluid flow rate actuated change over valve having one inlet, two outlets and a valve mechanism sensitive to the rate of fluid flow through the valve such that the discharge flow is directed into a low flow rate line or a high flow rate line dependent upon the rate of fluid flow.

Average Velocity Distribution of Turbulent Pipe Flow with Emphasis on the Viscous Sublayer

Abstract: A comprehensive experimental investigation is presented of the average velocity distribution of fully developed, smooth turbulent flows through straight pipes of circular cross section with special regard to the distribution within the viscous sublayer, including data at zero distance from the wall. The measurements seem to remove uncertainties and discrepancies inherent from earlier investigations. Current concepts of the universal velocity distribution are confirmed and verified.