摘要:

Drag measurements were made on circular cylinders in the range of Reynolds number Re (based on diameter) 0.23 to 2.6. Empirical corrections were used to account for the effects of finite boundaries and finite lengths. The boundary correction was small (<0.1%), but the length correction ranged up to 6.6%. The experimental results agree well with the theory of Kaplun for Re<0.5 and with the numerical results of Takami and Keller at Re=1 and 2.

ISSN:0031-9171    

DOI:10.1063/1.862001

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The largest vortex ring that can pass through a prescribed circular aperture in a thin infinite plane has been analyzed for an inviscid and incompressible fluid. A closed form solution for the velocity potential and the core velocity was obtained. Also given are typical core paths for both passing and nonpassing cases as well as a relation between the core and ring radii for the limiting case.

ISSN:0031-9171    

DOI:10.1063/1.862002

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A numerical calculation of the steady flow in a laminar boundary layer on a fixed circular disk of finite size induced by some external axially symmetric motion is presented. The flow external to the boundary layer consists of a potential vortex which is coincident with the axis of the disk and an inward radial motion proportional to a power of the distance from the axis,r−m. Integration of the boundary layer equations is carried out starting at the edge of the disk and proceeding inward until a terminal solution is obtained. A numerical technique is employed which allows a solution to be obtained very near the center despite the extreme thickness of the boundary layer. A surprising result is the apparent lack of dependence of the terminal solution on either the conditions at the edge of the disk or the value ofmform<1. The limiting case when the spin vanishes is also calculated and the results support the view of Brown and Stewartson that algebraic decay can exist at a singular point in the boundary layer.

ISSN:0031-9171    

DOI:10.1063/1.862003

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The velocity and temperature distributions in turbulent buoyant induced by a line source or point source of heat are calculated by assuming the eddy viscosity and eddy diffusivity to be constant in any cross section of the plume. Two solutions in closed forms are obtained for the two‐dimensional plume, corresponding to turbulent Prandtl number &sgr; equal to 2/3 and 2. Two such solutions are also obtained for the round plume, corresponding to &sgr; equal to 1.1 and 2. The solution for &sgr;=2/3 is compared with previous measurements for two‐dimensional plumes, and the solution for &sgr;=1.1 is compared with previous measurements for the axisymmetric plume. The analytical and experimental results agree well in the two‐dimensional case, and satisfactorily in the axisymmetric case.

ISSN:0031-9171    

DOI:10.1063/1.862004

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

All three components of the dissipation rate of the fluctuating temperature &Vthgr; are measured simultaneously in the inner region of a fully developed turbulent boundary layer at a moderate Reynolds number. Measurements are made with a probe of four cold wires consisting of two closely spaced parallel vertical wires mounted a small distance upstream of two closely spaced parallel horizontal wires. In the inner region of the layer, local isotropy is not closely approximated (∂&Vthgr;/∂z)2⟩ (∂&Vthgr;/∂y)2⟩ (∂&Vthgr;/∂x)2. The spectral density of the sum &khgr;[= (∂&Vthgr;/∂x)2+(∂&Vthgr;/∂y)2+ (∂&Vthgr;/∂z)2] is similar in shape to that of (∂&Vthgr;/∂y)2or (∂&Vthgr;/∂z)2but not as rich in high frequency content as that of (∂&Vthgr;/∂x)2. The probability density of &khgr; has a lower skewness and flatness factor and is more closely log‐normal than those of the individual components. This is true regardless of whether &khgr; and its components are unaveraged or locally averaged over a linear dimensionr. When averaging is applied, departures from log‐normality are diminished but do not disappear entirely. The variance &sgr;2of the logarithm of the locally averaged &khgr; is proportional to lnrover a wide range ofr(rmax/rmin≃30), in contrast to the individual components where this ratio may be as small as 2. The value of the Kolmogoroff constant &mgr;&Vthgr;determined from the slope of &sgr; vs lnris about 0.35. This is consistent with the slope of the spectral density of &khgr; and is also in agreement with previous best estimates of &mgr;&Vthgr;(and &mgr;) obtained at high Reynolds numbers.

ISSN:0031-9171    

DOI:10.1063/1.862005

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Under consistent truncation of the Fourier amplitude equations for the inviscid two‐dimensional flow, it is shown that the class of extraneous constants of motion associated with Hald’s model examples does not appear. Hence, the conclusion that total energy and enstrophy being the only isolating constants of two‐dimensional turbulence is still valid, until a new class of constants of motion is discovered.

ISSN:0031-9171    

DOI:10.1063/1.862006

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Equations for steady convection in a porous linear elastic matrix are formulated. When porosity changes are of the order of the pressure induced compressions in matrix and fluid, and these in turn can be neglected in comparison with thermal expansions in the fluid, the fluid balance laws uncouple from the equilibrium balance of the matrix. Plane flow in a horizontal layer is considered for temperature increases with depth up to 250°K, and the significant variations of viscosity and thermal expansion coefficients with temperature are included. The critical Rayleigh number for small disturbances harmonic in the horizontal direction is found to be substantially reduced from the constant expansion coefficient value, but the associated wavenumber and incipient flow patterns are little changed. However, if a Rayleigh number based on an appropriate mean value of the expansion coefficient is used, the critical values for constant and variable expansion coefficient solutions are in close agreement.

ISSN:0031-9171    

DOI:10.1063/1.862007

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The results of a straightforward investigation of heat transfer from hot wires in CO2–air mixtures, taking into consideration three parameters: velocity, temperature, and concentration are presented. Considering forced convection transfer, the final conclusion is expressed in the form of Nu=NA+NBRen.NA(Pr),NB(Pr), andn, are given and the observation of an overheat ratio, for which the composition sensitivity vanishes, is specified.

ISSN:0031-9171    

DOI:10.1063/1.862008

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Like‐particle diffusion is usually negligible compared with unlike‐particle diffusion because it is two orders higher in spatial derivatives. When the ratio of the ion gyroradius to the plasma transverse dimension is of the order of the fourth root of the mass ratio, previous one‐dimensional analysis indicated that like‐particle diffusion is significant. A two‐dimensional boundary‐value problem for ion‐ion diffusion is investigated. Numerical solutions are found with models for which the nonlinear partial differential equation reduces to an ordinary fourth‐order differential equation. These solutions indicate that the ion‐ion losses are higher by a factor of six for a slab geometry, and by a factor of four for circular geometry, than estimated from dimensional analysis. The solutions are applied to a multiple mirror experiment stabilized with a quadrupole magnetic field which generates highly elliptical flux surfaces. It is found that the ion‐ion losses dominate the electron‐ion losses and that these classical radial losses contribute to a significant decrease of plasma lifetime, in qualitiative agreement with the experimental results.

ISSN:0031-9171    

DOI:10.1063/1.862009

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The distribution function is determined numerically for electrons subject to magnetic trapping, electron‐electron, and electron‐ion collisions, and an electric field large enough to invalidate the Spitzer–Ha¨rm (classical) approximation. The electrical resistivity is determined. It is compared with analytical theory for tokamaks, in the limit of large inverse aspect ratio &egr;, and small drift velocityVd/Vth. The resistivity is plotted for values of &egr; andVd/Vthfor which no analytic theory is available.

ISSN:0031-9171    

DOI:10.1063/1.862010

出版商:AIP    

年代:1977

数据来源: AIP