Showing papers in "Journal of Fluids Engineering-transactions of The Asme in 1977"

The calculation of turbulent boundary layers on spinning and curved surfaces

Abstract: The development of turbulent shear layers on rotating or curved surfaces is usually characterized by strong effects of streamline curvature on the turbulence structure. The present contribution deals with the calculation of these effects with a model of turbulence which solves transport equations for the turbulence kinetic energy and its local rate of dissipation. The direct effect of curvature in the model is limited to a single empirical coefficient whose magnitude is directly proportional to a Richardson number based on a time scale of the energy-containing eddies. (In the absence of significant streamline curvature the model reduces to a form that has earlier been extensively tested in various thin shear flows.) Finite difference computations are reported of the following turbulent flows: the boundary layer on concave and convex surfaces; fully developed flow in a curved channel; axisymmetric flow over a spinning cylinder; and heat and mass transfer due to spinning cones of various vertex angles. Agreement with experiment is satisfactorily close in all these cases.

On the Growth of Steam Droplets Formed in a Laval Nozzle Using both Static Pressure and Light Scattering Measurements

Abstract: : A series of experiments on steam condensation have been made in a Laval nozzle over a variety of starting conditions such that the onset of condensation occurs in the range -40 to 40 C. The homogeneous nucleation and growth of the new phase is documented with both static pressure and laser light scattering. Since even at onset the majority of the condensed phase is due to droplet growth the nucleation and growth are coupled and the availability of two measured quantities is helpful in comparing a particular combination of nucleation rate and growth law. For detailed calculations on one of the experiments there is excellent agreement with both measurements throughout the condensation zone and a theoretical calculation using the classical nucleation rate expression due to Volmer and a droplet growth law due to Gyarmathy.

Influence of Inlet Flow Conditions and Geometries of Centrifugal Vaneless Diffusers on Critical Flow Angle for Reverse Flow

Abstract: The authors’ preceding analysis on centrifugal vaneless diffusers is used to examine the influences of diffuser geometries and of flow inlet conditions on the critical flow angle for reverse flow, and the results are presented in graphs. The diffuser width to radius ratio, the inlet Mach number, and the distortion of the inlet velocity distribution have significant influences on the critical flow angle, while the Reynolds number and the boundary layer thickness at the inlet have minor influences.

Design of Two-Dimensional Wind Tunnel Contractions

Abstract: Design charts for 2-D wind tunnel contractions have been developed using inviscid flow analysis, in which a one-parameter family of wall shapes, based on two cubic arcs, was investigated in detail. The design chart parameters are the maximum wall pressure coefficients at the inlet (as an indicator of the danger of separation at the inlet end) and at the exit (which is related to the exit velocity non-uniformity as well as to separation). For any choice of these two parameters the charts yield the shape parameter and the nozzle length for this particular family of shapes. The charts may be used to design nozzles with no flow separation and with any desired exit velocity uniformity. When the two pressure coefficients are chosen so that separation at both ends is just avoided, the exit boundary layer thickness should be near its minimum. Simple working forms of Stratford’s separation criteria are suggested for the prediction of separation. The results of this study are compared to those obtained earlier for axisymmetric geometries.

Vortex Excited Oscillations of Yawed Circular Cylinders

Abstract: Yawed cylinders are cylinders inclined forward or backwards in the plane of the flowing fluid. They are used in many practical situations such as braced frame members and raked marine piles. This paper describes an examination of three aspects of the yawed cylinder-fluid interactions over a range of yaw angles ±45° from the vertical for the Reynolds number range 2,000 < Re < 20,000. viz. 1. Establishment of the stability criteria of vortex-excited oscillations. 2. Measurement of ‘steady’ drag forces and equivalent drag coefficients. 3. Visualization of the local flow over stationary and oscillating cylinder. After a brief review of previous experimental and theoretical work, the results of the three items listed above are presented and discussed. Vortex-excited oscillations were recorded in the in-line and crossflow directions throughout the range of yaw angles and the results of items 2, 3 were used to justify the forms of the stability criteria proposed for these oscillations.

Numerical Computation of Flow in Rotating Ducts

Abstract: A finite-difference procedure is employed to predict the turbulent flaw in ducts of rectangular cross-section, rotating about an axis normal to the longitudinal direction. The flows were treated as “parabolic”; and the turbulence model used involved the solution of two differential equations, one for the kinetic energy of the turbulence and the other for its dissipation rate. Agreement with experimental data is good for a constant-area duct at low rotation, but less satisfactory for a divergent duct at larger rotation. It is argued that a “partially-parabolic” procedure will be needed to predict the latter flow correctly.

Experimental Study of Error Sources in Skin-Friction Balance Measurements

Abstract: An experimental study has been performed to determine potential error sources in skin-friction balance measurements. A floating-element balance, large enough to contain the instrumentation needed to systematically investigate these error sources has been constructed and tested in the thick turbulent boundary layer on the sidewall of a large supersonic wind tunnel. Test variables include element-to-case misalignment, gap size, and Reynolds number. The effects of these variables on the friction, lip, and normal forces have been analyzed. Results indicate that some of the intuitive assumptions generally held by designers and users of skin-friction balances may not be valid. For example, it was found that larger gap sizes were preferable to smaller ones; that small element recession below the surrounding test surface produced errors comparable to the same amount of protrusion above the test surface; and that normal forces on the element were, in some cases, large compared to the friction force. The principle contributions of this paper are (1) that users of skin-friction balances can use the data contained in this paper to estimate the errors involved in their measurements, and to make corrections if necessary, and (2) that the results of this study may lead to the development of new and improved devices for direct skin-friction measurement.

Investigations on Axial Flow Fan Impellers With Forward Swept Blades

Abstract: The forward swept blades are expected to reduce the accumulation of boundary layer fluid resulting from the effect of centrifugal forces, near the tip region of an axial flow impeller blade. An experimental study was carried out on three sets of impeller blades with different forward sweep, keeping the blade element profile geometry the same. It is seen from the comparison of the overall performance of the impellers with swept and unswept blades that the swept blades operate more efficiently than the unswept blades, especially at low volume flows. Moreover, the blade element stall is delayed, if the blades are swept forward. An analysis of the experimental results shows that forward sweep effectively reduces the deteriorating effects of the radially outward boundary layer flow in the tip region.

Dynamics of Heat Exchanger Tube Banks

Abstract: Flow-induced vibration in heat exchanger tube banks is of great concern, particularly in high performance heat exchangers used in nuclear reactor systems. The dynamic characteristics of tube banks in stationary liquid are studied. A method of analysis is presented for free and forced vibrations of tube banks including tube/fluid interaction. Numerical results are given for tube banks subjected to various types of excitations.