Calculation of Variable Property Turbulent Friction and Heat Transfer in Rough Pipes

1979 ◽  
Vol 101 (3) ◽  
pp. 469-474 ◽  
Author(s):  
A. T. Wassel ◽  
A. F. Mills
Keyword(s):  
Roughness Element ◽  
Gas Flows ◽  
Mixing Length ◽  
Variable Properties ◽  
Turbulent Friction ◽  
Variable Property ◽  
Comparison With Experiment ◽  
Large Roughness ◽  
Pipe Radius ◽  
Numerical Calculation Method

A numerical calculation method for turbulent flow in rough pipes is developed. A mixing length model is used in the turbulent core while a roughness element drag coefficient and a sub-layer Stanton number are used to characterize transport to the wall. Sample wall relations are developed for sandgrain roughness and transverse repeated rib roughness, and it is shown that large roughness heights require accounting for terms of order of roughness height divided by pipe radius. For gas flows with cooling, the effects of variable properties are investigated for smooth walls and both roughness patterns. For smooth walls, comparison with experiment is satisfactory; for rough walls experimental data is not available. Simple power law formulae representing variable property effects for fully rough flows are presented.

Large roughness element effects on sand transport, Oceano Dunes, California

2012 ◽  
Vol 38 (8) ◽  
pp. 785-792 ◽  
Author(s):  
John A. Gillies ◽  
Nicholas Lancaster
Keyword(s):  
Roughness Element ◽  
Sand Transport ◽  
Large Roughness

TURBULENT VARIABLE PROPERTY GAS FLOWS

1986 ◽  
Vol 42 (4-6) ◽  
pp. 315-332
Author(s):  
MOUNIR B. IBRAHIM ◽  
LINDON C. THOMAS
Keyword(s):  
Gas Flows ◽  
Variable Property

Effect of Variable Properties Within a Boundary Layer With Large Freestream-to-Wall Temperature Differences

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Nathan J. Greiner ◽  
Marc D. Polanka ◽  
James L. Rutledge ◽  
Jacob R. Robertson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flows ◽  
Wall Temperature ◽  
Ratio Method ◽  
Variable Properties ◽  
Temperature Ratio ◽  
Adiabatic Wall ◽  
Constant Property ◽  
Variable Property

Modern gas-turbine engines are characterized by high core-flow temperatures and significantly lower turbine-surface temperatures. This can lead to large property variations within the boundary layers on the turbine surfaces. However, cooling of turbines is generally studied near room temperature, where property variation within the boundary layer is negligible. The present study first employs computational fluid dynamics to validate two methods for quantifying the effect of variable properties in a boundary layer: the reference temperature method and the temperature ratio method. The computational results are then used to expand the generality of the temperature ratio method by proposing a slight modification. Next, these methods are used to quantify the effect of variable properties within a boundary layer on measurement techniques, which assume constant properties. Both low-temperature flows near ambient and high-temperature flows with a freestream temperature of 1600 K are considered under both laminar and turbulent conditions. The results show that variable properties have little effect on laminar flows at any temperature or turbulent flows at low temperatures such that constant property methods can be validly employed. However, variable properties are seen to have a profound effect on turbulent flows at high temperatures. For the high-temperature turbulent flow considered, the constant property methods are found to overpredict the convective heat transfer coefficient by up to 54.7% and underpredict the adiabatic wall temperature by up to 209 K. Utilizing the variable property techniques, a new method for measuring the adiabatic wall temperature and variable property heat-transfer coefficient is proposed for variable property flows.

In Situ Observation of Catalyzed Gasification of Graphite by Nickel

1981 ◽  
Vol 39 ◽  
pp. 76-77
Author(s):  
R. T. K. Baker ◽  
R. D. Sherwood
Keyword(s):  
Objective Lens ◽  
In Situ Observation ◽  
Gas Flows ◽  
Catalytic Gasification ◽  
Television Camera ◽  
Viewing Screen ◽  
Fuels And Chemicals ◽  
Gasification Of Carbon ◽  
Transmission Microscope

The catalytic gasification of carbon at high temperature by microscopic size metal particles is of fundamental importance to removal of coke deposits and conversion of refractory hydrocarbons into fuels and chemicals. The reaction of metal/carbon/gas systems can be observed by controlled atmosphere electron microscopy (CAEM) in an 100 KV conventional transmission microscope. In the JEOL gas reaction stage model AGl (Fig. 1) the specimen is positioned over a hole, 200μm diameter, in a platinum heater strip, and is interposed between two apertures, 75μm diameter. The control gas flows across the specimen and exits through these apertures into the specimen chamber. The gas is further confined by two apertures, one in the condenser and one in the objective lens pole pieces, and removed by an auxiliary vacuum pump. The reaction zone is <1 mm thick and is maintained at gas pressure up to 400 Torr and temperature up to 1300<C as measured by a Pt-Pt/Rh 13% thermocouple. Reaction events are observed and recorded on videotape by using a Philips phosphor-television camera located below a hole in the center of the viewing screen. The overall resolution is greater than 2.5 nm.

Saturation mechanism and generated viscosity in gravito-turbulent accretion disks

2020 ◽  
Vol 640 ◽  
pp. A53
Author(s):  
L. Löhnert ◽  
S. Krätschmer ◽  
A. G. Peeters
Keyword(s):  
Growth Rate ◽  
Numerical Simulations ◽  
Accretion Disks ◽  
Gravitational Instability ◽  
Turbulent Viscosity ◽  
Radial Distance ◽  
Maximum Growth ◽  
Wave Number ◽  
Radiative Cooling ◽  
Mixing Length

Here, we address the turbulent dynamics of the gravitational instability in accretion disks, retaining both radiative cooling and irradiation. Due to radiative cooling, the disk is unstable for all values of the Toomre parameter, and an accurate estimate of the maximum growth rate is derived analytically. A detailed study of the turbulent spectra shows a rapid decay with an azimuthal wave number stronger than ky−3, whereas the spectrum is more broad in the radial direction and shows a scaling in the range kx−3 to kx−2. The radial component of the radial velocity profile consists of a superposition of shocks of different heights, and is similar to that found in Burgers’ turbulence. Assuming saturation occurs through nonlinear wave steepening leading to shock formation, we developed a mixing-length model in which the typical length scale is related to the average radial distance between shocks. Furthermore, since the numerical simulations show that linear drive is necessary in order to sustain turbulence, we used the growth rate of the most unstable mode to estimate the typical timescale. The mixing-length model that was obtained agrees well with numerical simulations. The model gives an analytic expression for the turbulent viscosity as a function of the Toomre parameter and cooling time. It predicts that relevant values of α = 10−3 can be obtained in disks that have a Toomre parameter as high as Q ≈ 10.

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