Wall-shear-stress and near-wall turbulence measurements up to single pixel resolution by means of long-distance micro-PIV

A digital large-format long-distance micro-particle image velocimetry system (μ-PIV) was developed to measure the wall-shear-stress and the near-wall flow properties in a laminar, transitional and turbulent boundary layer flow along a flat plate, non-intrusively with high accuracy and spatial resolution. To achieve the desired measurement accuracy and spatial resolution, all experimental limitations associated with the seeding, light-sheet, out-of-focus particles, optical aberrations and distortions were successfully solved and various spatial correlation image analysis approaches based on the two-point or single-pixel ensemble correlation were developed, analyzed and compared with the state-of-the-art spatial correlation techniques. The instrument is well suited to prove fundamental fluid mechanical hypotheses such as the universality of the constants κ and B of the logarithmic law. However, for the analysis of flows at large Reynolds and Mach numbers, where small spatial dimensions and strong flow gradients prevent accurate measurements, this technique can be applied as well.     

Vehicle and machinery design; Implements

After a general introduction the papers presented at Session IV of the 9th International ISTVS Conference concerned with “Vehicle and Machinery Design”, are discussed in groups, based on field of application. Special attention is paid to instrumentation and implementation of measurements.     

„Fouling“-Vorgänge bei der Verdampfung von Argon im waagerecht durchströmten Rohr

Zusammenfassung Bei Messungen des Wärmeübergangs beim Strömungssieden von Argon wurde ein zeitlicher Anstieg der Wandtemperatur beobachtet, während die Einstellparameter Wärmestromdichte, Massenstromdichte, Dampfgehalt und Systemdruck konstant blieben. Dieser Temperaturanstieg endete nach mehreren Stunden bei einer beträchtlich höheren Wandtemperatur oder mit dem Eintreten der Siedekrise. Als Ursache für dieses Phänomen wurde die Ablagerung von im Argon gelöstem CO₂ an der Heizfläche ermittelt, wobei zu beachten ist, daß die Reinheit des verwendeten Argons größer als 99,996 vol-% war. In weiteren Versuchen wurde der Einfluß der CO₂-Konzentration auf diesen Fouling-Vorgang bestimmt und ein Verfahren entwickelt, um das CO₂ aus dem Meßkreislauf zu entfernen. Der Ablagerungsmechanimus und der Einfluß der Betriebsparameter auf die Ablagerungsgeschwindigkeit können mit Modellvorstellungen zur Blasenbildung erklärt werden.

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Fouling-phenomena during the evaporation of argon within a horizontal tube

During heat transfer measurements at flow boiling of argon a transient increase of the wall temperature has been observed, though the parameters such as heat flux, mass velocity, flow quality and system pressure were kept constant. This temperature drifting ended after several hours at a considerably higher wall temperature or with the boiling crisis. Although the purity of the test substance was higher than 99.996 vol-%, this phenomenon was caused by the solidification of CO₂ on the heating surface. Further investigations showed the influence of the CO₂-concentration on the drifting as well as a method to remove the CO₂ out of the test fluid. Both, fouling mechanism and influence of the parameters on the fouling, can be explained satisfactorily by means of bubble-growth mechanisms.

     

Optimum conditions of turbulence reduction with screens

The results of an experimental investigation of the conditions of flow turbulence suppression with a set of screens, each of which operates in the optimum regime, are presented. Recommendations are made concerning the choice of the number of screens in the set, their geometric parameters and their location in the flow which guarantee the most efficient reduction of free-stream turbulence.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.1, pp. 181–191, January–February, 1993.     

Boundary-layer transition on a cylinder with and without separation bubbles

Boundary layer transition with and without transitional separation bubbles was investigated on a cylinder in cross flow. Measurements of the pressure distribution and hot-wire measurements within the boundary layer were carried out at two free-stream velocities and with different flow disturbances. The separation bubble reacts very sensitively to changes in inlet turbulence. Tollmien-Schlichting waves were observed in the separated shear layer just before transition, and their frequencies were in good agreement with stability theory. However, correlations concerning bubble length which were fitted using airfoil data are apparently not suitable for describing separation bubbles on cylinders. Finally, measurements in periodically disturbed flow show how the bubble reacts to this type of disturbance.     

Stretching of squeezed liquid under the action of its own weight

The stretching of a liquid sample, squeezed out in the vertical direction from an aperture of an arbitrary form, is investigated. The problem of controlling the dimensions of the aperture or the rate of squeezing for obtaining samples of a given configuration is discussed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 10–14, September–October, 1975.     

Numerical modeling of carbon monoxide neutralization by metered water injection into a high-temperature mixture of combustion products

A closed mathematical model of the flow of a two-phase mixture consisting of evaporating water droplets and a chemically reacting multicomponent gas is described. The effect of the real droplet heating and evaporationkinetics on the gas-phase chemical reactions in a mixture of combustion products is studied within the framework of this model.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.6, pp. 96–106, November–December, 1993.     

Method of calculating the contours of aerodynamic nozzles with transition through the velocity of sound

The existing methods of constructing an “ideal” contour (i.e., a contour without taking account of viscosity) for aerodynamic nozzles has a number of drawbacks: they are extremely unwieldly and are not versatile and, moreover, they give in practice an impairment of the flow uniformity, caused by nonconformity of the true flow in the transonic region assumed in the solution, as only the hypersonic flow region is usually calculated. In this paper, a method is proposed for calculating the ideal contours of aerodynamic nozzles with transition through the velocity of sound, which is free from these drawbacks. Cauchy's problem is solved numerically by the method in [1]. A specially corrected pressure distribution, obtained experimentally [2], is used as the initial distribution. Examples of the calculation are given for the ideal contours of plane, axisymmetrical and annular aerodynamic nozzles.     

Experimental investigation of the development of motion of liquid in conduits

Only a few studies have been devoted to the experimental study of the initial stage of the motion of a liquid from the state of rest in a closed delivery conduit [1]. It can be concluded on the basis of the results of these studies that at the beginning of the process the mechanical energy losses are smaller than in quasistationary flow. These studies also suggest that the laminar nature of the flow persists in the nonstationary flow. However, investigations are of an integral nature and therefore in them the flow structure is not determined. In the present study the development of the motion of the liquid in a delivery conduit from the state of rest is investigated. The tangential frictional stresses at the wall of the conduit, measured by the thermal anemometric method, show that the transitional Reynolds number, at which the laminar flow regime changes into turbulent, depends on the acceleration of the flow and far exceeds the critical value for the case of the stationary flow. At maximum acceleration of the flow equal to 11.78 m/sec² the transition of the laminar regime to the turbulent at the wall of the conduit occurs at Re = 234, 500. The loss coefficients of mechanical energy have been computed from experimental results, which show that the use of the corresponding coefficient of quasistationary turbulent flow in the computation leads to appreciable errors.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 79–85, November–December, 1977.     

Laval nozzle flow calculation

The inverse problem of the theory of the Laval nozzle is considered, which leads to the Cauchy problem for the gasdynamic equations; the streamlines and the flow parameters are found from the known velocity distribution on the axis of symmetry.The inverse problem of Laval nozzle theory was considered in 1908 by Meyer [1], who expanded the velocity potential into a series in powers of the Cartesian coordinates and constructed the subsonic and supersonic solutions in the vicinity of the center of the nozzle. Taylor [2] used a similar method to construct a flowfield which is subsonic but has local supersonic zones in the vicinity of the minimal section. Frankl [3] and Fal'kovich [4] studied the flow in the vicinity of the nozzle center in the hodograph plane. Their solution, just as the Meyer solution, made it possible to obtain an idea of the structure of the transonic flow in the vicinity of the center of the nozzle.A large number of studies on transonic flow in the vicinity of the center of the nozzle have been made using the method of small perturbations. The approximate equation for the transonic velocity potential in the physical plane, obtained in [3–6], has been studied in detail for the plane and axisymmetric cases. In [7] Ryzhov used this equation to study the question of the formation of shock waves in the vicinity of the center of the nozzle, and conditions were formulated for the plane and axisymmetric cases under which the flow will not contain shock waves. However, none of the solutions listed above for the inverse problem of Laval nozzle theory makes it possible to calculate the flow in the subsonic and transonic parts of the nozzles with large gradients of the gasdynamic parameters along the normal to the axis of symmetry.Among the studies devoted to the numerical calculation of the flow in the subsonic portion of the Laval nozzle we should note the study of Alikhashkin et al., and the work of Favorskii [9], in which the method of integral relations was used to solve the direct problem for the plane and axisymmetric cases.The present paper provides a numerical solution of the inverse problem of Laval nozzle theory. A stable difference scheme is presented which permits analysis with a high degree of accuracy of the subsonic, transonic, and supersonic flow regions. The result of the calculations is a series of nozzles with rectilinear and curvilinear transition surfaces in which the flow is significantly different from the one-dimensional flow. The flowfield in the subsonic and transonic portions of the nozzles is studied. Several asymptotic solutions are obtained and a comparison is made of these solutions with the numerical solution.The author wishes to thank G. D. Vladimirov for compiling the large number of programs and carrying out the calculations on the M-20 computer.