Effect of Free-Stream Velocity Vector and Aspect Ratio on the Output of a Free-Standing Circular Disk Heat Flux Gage

1984 ◽  
Vol 106 (1) ◽  
pp. 229-233 ◽  
Author(s):  
M. F. Young
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Free Stream ◽  
Angle Of Attack ◽  
Circular Disk ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Free Standing

The effects of free-stream velocity, angle of attack, and aspect ratio on the output of a free-standing circular disk heat flux gage subjected to a combined radiative and convective heat flux are reported. The Reynolds number range investigated extends from 6000 to 25,000, while the gage angle of attack was varied from 0 to 90 deg. Results for three gage aspect ratios, 5.85, 8.77, and 11.76, are presented. The Nusselt number is used to represent the effects of convection on the gage output. The Nusselt number was found to increase with increasing Reynolds number and angles of attack. At an angle of attack of about 90 deg, however, a significant reduction in the Nusselt number was noted. A correlation relating the Nusselt number (based on the disk diameter) to the Reynolds number (based on the gage outside diameter) and the angle of attack is reported. This correlation represents the data to within ±5 percent.

Unsteady drag on a sphere at finite Reynolds number with small fluctuations in the free-stream velocity

1991 ◽  
Vol 233 ◽  
pp. 613-631 ◽  
Author(s):  
Renwei Mei ◽  
Christopher J. Lawrence ◽  
Ronald J. Adrian
Keyword(s):  
Reynolds Number ◽  
Free Stream ◽  
Low Frequency ◽  
Reynolds Numbers ◽  
Free Stream Velocity ◽  
Creeping Flow ◽  
Stream Velocity ◽  
Velocity Difference ◽  
Long Time ◽  
The Time Domain

Unsteady flow over a stationary sphere with small fluctuations in the free-stream velocity is considered at finite Reynolds number using a finite-difference method. The dependence of the unsteady drag on the frequency of the fluctuations is examined at various Reynolds numbers. It is found that the classical Stokes solution of the unsteady Stokes equation does not correctly describe the behaviour of the unsteady drag at low frequency. Numerical results indicate that the force increases linearly with frequency when the frequency is very small instead of increasing linearly with the square root of the frequency as the classical Stokes solution predicts. This implies that the force has a much shorter memory in the time domain. The incorrect behaviour of the Basset force at large times may explain the unphysical results found by Reeks & Mckee (1984) wherein for a particle introduced to a turbulent flow the initial velocity difference between the particle and fluid has a finite contribution to the long-time particle diffusivity. The added mass component of the force at finite Reynolds number is found to be the same as predicted by creeping flow and potential theories. Effects of Reynolds number on the unsteady drag due to the fluctuating free-stream velocity are presented. The implications for particle motion in turbulence are discussed.

Experiments on Leading-Edge Induced Separated Shear Layer Under Various Imposed Pressure Gradients

2014 ◽  
Author(s):  
K. Anand ◽  
S. Sarkar ◽  
N. Thilakan
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Free Stream ◽  
Separation Bubble ◽  
Leading Edge ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Pressure Gradients ◽  
Mean Flow ◽  
Separated Shear Layer

The behaviour of a separated shear layer past a semi-circular leading edge flat plate, its transition and reattachment downstream to separation are investigated for different imposed pressure gradients. The experiments are carried out in a blowing tunnel for a Reynolds number of 2.44×105 (based on chord and free-stream velocity). The mean flow characteristics and the instantaneous vector field are documented using a two-component LDA and a planar PIV, whereas, surface pressures are measured with Electronically scanned pressure (ESP). The onset of separation occurs near the blend point for all values of β (flap angle deflection), however, a considerable shift is noticed in the point of reattachment. The dimensions of the separation bubble is highly susceptible to β and plays an important role in the activity of the outer shear layer. Instantaneous results from PIV show a significant unsteadiness in the shear layer at about 30% of the bubble length, which is further amplified in the second half of the bubble leading to three-dimensional motions. The reverse flow velocity is higher for a favourable pressure gradient (β = +30°) and is found to be 21% of the free stream velocity. The Reynolds number calculated based on ll (laminar shear layer length), falls in the range of 0.9×104 to 1.4×104. The numerical values concerning the criterion for separation and reattachment agree well with the available literature.

On the Resistance of Screens

1953 ◽  
Vol 4 (2) ◽  
pp. 186-192 ◽  
Author(s):  
K. E. G. Wieghardt
Keyword(s):  
Reynolds Number ◽  
Average Velocity ◽  
Free Stream ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Single Piece ◽  
Experimental Function ◽  
Almost All

Summary The resistance of various screens in a tube is reduced to the drag of a single piece of wire by assuming that the average velocity in the screen itself rather than the free stream velocity is the significant factor. Almost all the available tests on screens or gauzes are brought into line with a single experimental function similar to the drag of a cylinder plotted against Reynolds number.

Approximate Solution to a Class of Transient Forced Convection Problems

1977 ◽  
Vol 99 (4) ◽  
pp. 567-574 ◽  
Author(s):  
J. Sucec
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Surface Temperature ◽  
Forced Convection ◽  
Free Stream ◽  
The Body ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Response Curves ◽  
Constant Property

Approximate solutions using integral methods and the method of characteristics are found for the case of laminar, low speed, constant property, two-dimensional planar boundary layer type flow over a body which is initially at the constant temperature of the fluid passing over it and then, suddenly, has its surface temperature changed to a new constant value or has a constant heat flux imposed at the surface. The free stream velocity is variable with position along the body and the entire velocity field is assumed to be in the steady state. Response curves for surface heat flux or of surface temperature as a function of position and time are presented for power law variations of free stream velocity (the “wedge” type flows) and also for one particular nonsimilar (nonwedge) case. The relative ease with which the nonsimilar cases can be handled is thought to make the approach, advanced herein, a useful tool for the engineer to attack other nonsimilar cases. It was also found that the use of an “equivalent” wedge variable gives reasonably satisfactory results for the nonsimilar case chosen. Hence the application of the equivalent wedge methods is valid for transient forced convection problems just as it is, as is well known, for steady-state forced convection.

Bioconvection in Casson nanofluid flow with Gyrotactic microorganisms and variable surface heat flux

2019 ◽  
Vol 12 (04) ◽  
pp. 1950041 ◽  
Author(s):  
I. S. Oyelakin ◽  
S. Mondal ◽  
P. Sibanda ◽  
D. Sibanda
Keyword(s):  
Heat Flux ◽  
Vertical Plate ◽  
Free Stream ◽  
Free Stream Velocity ◽  
Convection Flow ◽  
Stream Velocity ◽  
Constant Density ◽  
Gyrotactic Microorganisms ◽  
Casson Nanofluid ◽  
Variable Surface

This paper presents a two-dimensional unsteady laminar boundary layer mixed convection flow heat and mass transfer along a vertical plate filled with Casson nanofluid located in a porous quiescent medium that contains both nanoparticles and gyrotactic microorganisms. This permeable vertical plate is assumed to be moving in the same direction as the free stream velocity. The flow is subject to a variable heat flux, a zero nanoparticle flux and a constant density of motile microorganisms on the surface. The free stream velocity is time-dependent resulting in a non-similar solution. The transport equations are solved using the bivariate spectral quasilinearization method. A grid independence test for the validity of the result is given. The significance of the inclusion of motile microorganisms to heat transfer processes is discussed. We show, inter alia, that introducing motile microorganisms into the flow reduces the skin friction coefficient and that the random motion of the nanoparticles improves the rate of transfer of the motile microorganisms.

scholarly journals Numerical Analysis of Aerodynamic Performance Characteristics of NACA 2312 and NACA 2412

2020 ◽  
Vol 5 (3) ◽  
pp. 420-428
Author(s):  
Pritam Saha ◽  
Harshpreet Singh Kaberwal
Keyword(s):  
Reynolds Number ◽  
Numerical Analysis ◽  
Free Stream ◽  
Angle Of Attack ◽  
Aerodynamic Performance ◽  
Performance Characteristics ◽  
Stream Velocity ◽  
Flow Conditions ◽  
Wing Design ◽  
Aerodynamic Modelling

Comparison of the Aerodynamic Performance characteristics of NACA 2312 and NACA 2412 aerofoils under the same flow conditions at a Reynolds number of 2.74 x 106 is presented. ANSYS is used for the creation of geometry and meshing and FLUENT is used as a solver. Coefficient of lift and coefficient of drag for both aerofoils are compared for a range of Angle of Attack while the free stream velocity of air is kept constant. This analysis can be used for the wing design and other aerodynamic modelling corresponds to these aerofoils.

On the asymptotic similarity of the zero-pressure-gradient turbulent boundary layer

2008 ◽  
Vol 616 ◽  
pp. 195-203 ◽  
Author(s):  
M. B. JONES ◽  
T. B. NICKELS ◽  
IVAN MARUSIC
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Similarity Solution ◽  
Friction Velocity ◽  
Free Stream ◽  
Outer Region ◽  
Free Stream Velocity ◽  
Stream Velocity

We investigate similarity solutions for the outer part of a zero-pressure-gradient turbulent boundary layer in the limit of infinite Reynolds number. Previous work by George (Phil. Trans. R. Soc. vol. 365, 2007 p. 789) has suggested that the only appropriate velocity scale for the outer region is U1, the free-stream velocity. This is based on the fact that scaling with U1 leads to a mathematically valid similarity solution of the momentum equation for the outer region in the asymptotic limit of infinite Reynolds number. Here we show that the classical scaling using the friction velocity also leads to a valid similarity solution for the outer flow in this limit. Therefore on this basis it is not possible to dismiss the friction velocity as a possible scaling as has been suggested by George (2007) and others. We show that both the free-stream velocity and the friction velocity are potentially valid scalings according to this theoretical criterion.

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