Die turbulente Grenzschicht an einer stark geheizten ebenen Platte bei Unterschallströmung

Experiments for air flowing over a flat plate heated up to 250°C with velocities of 10 to 30 m/s, which have been made at the DFVLR-AVA, are briefly reviewed and a new analysis of the data is given. The analysis is based on an analytical representation of the velocity and temperature profiles. Close to the wall, a law of the wall approximation is used, which includes the effect of density and viscosity variation. The whole velocity profile is constructed by adding Coles' law of the wake to the law of the wall. In a similar way, the temperature profile is obtained from the law of the wall and an auxiliary distribution. The integrals of momentum and heat flux for two-dimensional flow are used in conjunction with a similarity assumption, to derive a relation between rate of heat transfer from the plate and skin friction. A maximum likelihood procedure has been applied to determine skin friction and rate of heat transfer from the measured dynamic pressure profiles.—The analytical velocity and temperature profiles are found in good agreement with the experimental data, except for the stations near the leading edge of plate. The skin friction coefficients and the Stanton numbers decrease slightly in downstream direction as a consequence of growing local Reynolds number, and decrease with increasing ratio of plate to free stream temperature. The latter fact is in qualitative agreement with the behavior of turbulent boundary layers in supersonic flow. The ratio of Stanton number to half of skin friction coefficient (Reynolds analogy factor) varies with increasing local boundary layer Reynolds number from 1.23 to 1.16.     

A flow pattern map for gas—liquid flow in horizontal pipes

Various flow pattern maps for two-phase gas—liquid flow in horizontal pipes are tested against the 5935 flow pattern observations presently contained in the UC Multiphase Pipe Flow Data Bank.A new flow regime correlation representing an extension of the work done by Govier and Aziz [3] is presented and is shown to be in better agreement with the data than the other correlations tested. A computer program for this correlation is included.It is also shown that there is no significant improvement obtained by including the effects of the physical properties of the fluids using any of the physical property parameters which have been proposed so far.     

Stability of combustion of powder in a phenomenological model with nonadiabatic flame

A stability criterion for combustion of powder is obtained, taking into account the effect of the processes in the gas phase. It is shown that consideration of the effects of a nonadiabatic flame leads to the stability reserve of combustion being reduced and the natural frequency of vibrations being lowered. The effects thus found are physically explained by the radiation of a part of energy from the combustion zone with thermal and acoustic waves.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 82–87, November–December, 1973.Deceased.     

Experimental investigation of the resistance to the flow of a conducting fluid in flat insulated ducts in the presence of a transverse magnetic field with allowance for fringe effects and wall roughness

The distribution of pressure, velocity, and electrical potential has been investigated for a mercury flow in insulated rectangular ducts with a large side ratio (Hartmann-type flow). The ranges of variation of the Reynolds, Hartmann, and Stewart numbers were 7·10²R5·10⁵, 0H490, and 0N24, respectively. Special attention is given to the sections of the channel where the flow enters and leaves the magnetic field. In these zones the pressure is sharply nonuniform and the velocity profiles in a plane perpendicular to the field acquire an M shape. A relation is established between the length of the entrance section, where the flow is three-dimensional, and the MHD similarity criteria. It is shown that ducts which are hydraulically smooth in the absence of a magnetic field become increasingly rough as the field grows stronger. Data are obtained on the resistance coefficient for a stabilized flow measured in a magnetic field and on the dependence of the critical Reynolds number on the Hartmann number.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 10–21, July–August, 1971.     

Some rheological properties of dilute suspensions of polyoxymethylene crystals in p-xylene

Summary Dilute suspensions of polyoxymethylene crystals inp-xylene have been shown to behave as Bingham Plastic Fluids. The crystals are very thin hexagonal platelets and low concentrations are sufficient to provide a continuous high-voidage matrix which requires the application of a finite stress before deformation occurs. The behaviour of the system has been characterised with respect to changes in shear rate, temperature and concentration of suspended polymer.

---

Zusammenfassung Es wurde gezeigt, daß sich verdünnte Lösungen von Polyoxymethylen-Kristallen in p-Xylol wie eine Bingham-Flüssigkeit verhalten. Die Kristalle sind sehr dünne hexagonale Plättchen. Niedrige Konzentrationen sind für eine beständige Matrix, die das Aufbringen einer endlichen Spannung erfordert, bevor eine Deformation auftritt, ausreichend. Das Verhalten dieses Systems wurde unter Berücksichtigung von Änderungen der Schergeschwindigkeit, der Temperatur und der Konzentration des suspendierten Polymers charakterisiert.

     

Theory of nonlinear waves in a plasma

Stationary nonlinear waves propagating in a cold rarefied plasma composed of electrons and two types of ions are considered. The structure of isolated waves and shock waves is found. In recent years an intensive study has been made of finite-amplitude waves and collisionless shock waves in a rarefied plasma, in connection with laboratory experiments [1] and astrophysical applications (the problem of the interaction of the solar wind with the Earth's magnetosphere [2]). When allowance is made for dispersion effects associated with the departure of the dispersion law =(k) from the linear, and for the compensating nonlinear twisting of the wave profile, we are able to obtain the profile of stationary nonlinear waves of finite amplitude, and when allowance is made for damping we can also obtain the structure of a collisionless shock wave [3]. Such waves have been studied fairly fully for the case of a two-component plasma. The present paper examines stationary nonlinear waves propagating across a magnetic field in a cold rarefied quasi-neutral plasma composed of electrons and two types of ions.