摘要:

The analysis of drag reduction produced by high molecular weight fractions of Polyox shows that the slope of the drag reduction curve on a von Ka´rma´n plot for a narrow fraction is proportional to concentration and molecular weight. Polydisperse polymer solutions have drag reduction curves characteristic of the high molecular weight tail alone. Experimental results are presented on the shape of the distribution and the drag reduction of cumulative fractions containing the highest molecular weights.

ISSN:0031-9171    

DOI:10.1063/1.861940

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Velocity and pressure distributions are derived in an infinitely long swirl as functions of space and time by postulating an expression for turbulent stresses and neglecting laminar stresses. Constant angular momentum per unit distance along the swirl axis appears as a parameter.

ISSN:0031-9171    

DOI:10.1063/1.861941

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

It is shown that certain existing phenomenological models of turbulence in terms of differential equations for the Reynolds stressesR&agr;&bgr;=⟨u′&agr;u′&bgr;⟩ do not guarantee realizable solutions. The known realizability conditions areR&agr;&bgr;⩾0 for &agr;=&bgr; andR&agr;&bgr;2⩾R&agr;&agr;R&bgr;&bgr;for &agr;≠&bgr;. A stronger requirement is that the matrixR&agr;&bgr;be positive semi‐definite. This implies three conditions like non‐negative eigenvalues or non‐negative principal invariants. Conditions are given which must be satisfied by the model itself in order to guarantee realizable solutions for any realizable initial and boundary conditions. Some means are proposed which can be used to change the existing models into realizable ones.

ISSN:0031-9171    

DOI:10.1063/1.861942

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Similarity solutions to the incompressible axisymmetric Navier–Stokes equations have been obtained for the case of laminar flow in porous rotating annuli. The equations are reduced to a nonlinear ordinary differential system which is solved by a parametric differentiation method. The effect of radius ratio, radial Reynolds number, and the ratio of the radial flow rates at the two walls is investigated. For net injection the solutions are unique and tend to known asymptotic solutions. For net suction, regions of reversed flow are present and a multiplicity of solutions is encountered.

ISSN:0031-9171    

DOI:10.1063/1.861943

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A systematic perturbation expansion is developed for the steady‐state Navier–Stokes equations describing shock propagation in an ideal gas. The temperature dependence of the viscosity and thermal conductivity is accounted for, although the specific heat and Prandtl number are assumed constant. It is shown that if the firstn−1 terms in the expansion are known, thenth term can always be expressed in terms of a quadrature. Explicit calculation of the expansion is carried out to second order in the shock strength, and the results are compared with other calculations. It is shown that the results are in surprisingly good agreement with more exact calculations even for rather strong shock waves. The effect on shock structure of the temperature‐dependent transport coefficients is discussed.

ISSN:0031-9171    

DOI:10.1063/1.861944

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The equations for the triad resonance interactions of gravity‐capillary waves are derived by the Krylov–Bogoliubov–Mitropolski method. Some special two‐dimensional solutions are found.

ISSN:0031-9171    

DOI:10.1063/1.861945

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A Ba¨cklund transformation for the resonant three‐wave equations is derived. Both bounded and shock‐type solitons are obtained. For the shock‐type solitons, special two‐soliton solutions reveal that solitons can be created or annihilated.

ISSN:0031-9171    

DOI:10.1063/1.861946

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Collisions between two equal Langmuir solitons with opposite velocities are studied numerically, as a function of soliton strength, velocity, and relative phase angle. The computations show that all three parameters are important in the outcome of a collision, for which qualitative estimates are given.

ISSN:0031-9171    

DOI:10.1063/1.861947

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Intense Langmuir waves in a uniform, one‐dimensional plasma are described by a nonlinear Schro¨dinger equation. When the effect of linear damping is included, steady‐state shock wave solutions are found. Infinitely extended shock waves are produced by Landau damping; these shocks are moving with respect to the laboratory frame. Semi‐infinitely extended shock waves are produced by either collisional or Landau damping; these shocks are stationary in the laboratory frame, and have an energy flux through the boundary.

ISSN:0031-9171    

DOI:10.1063/1.861948

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The classical transport law for the hydrodynamic description of the electron heat flux breaks down in the nonequilibrium laser fusion plasma and an alternative expression for the electron heat flux vector must be used. Thead‐hocflux limit treatment used in present production level codes is analyzed and shown to provide physically plausible results but without providing any further insight into the properties of the plasma. Grad’s 13 moment method is proposed as an alternative to the conventional Fourier’s law expression for the heat flux. Numerical calculations confirm that this approach not only provides physically plausible results but provides them within a more fundamental framework than thead‐hocflux limiting schemes and thus offers the possibility of gaining more insight into the flux limiting mechanism.

ISSN:0031-9171    

DOI:10.1063/1.861949

出版商:AIP    

年代:1977

数据来源: AIP