Heat transfer in film-cooled turbulent boundary layers at different blowing ratios as affected by longitudinal vortices

Effects of embedded longitudinal vortices on heat transfer in film-cooled turbulent boundary layers at different blowing ratios are discussed. These results were obtained in boundary layers at free-stream velocities of 10 and 15 m/s. Film coolant was injected from a single row of holes at blowing ratios of 0.47–1.26. A single longitudinal vortex was induced upstream of the film-cooling holes using a half-delta wing attached to the wind tunnel floor. Heat transfer measurements were made downstream of injection using a constant heat flux surface with 126 thermocouples for surface temperature measurements. For all blowing ratios examined, the embedded vortices cause significant alterations to wall heat transfer and to film cooling distributions. Measurrments of mean temperatures and mean velocities in spanwise planes show that high wall heat transfer regions are associated with regions of high near-wall longitudinal velocity where very little film coolant is present. In addition to high heat transfer regions associated with the vortex downwash, there are also secondary heat transfer peaks. These secondary peaks develop due to shear layer mixing and interaction between the vortex and cooling jets and become higher in magnitude and more persistent with downstream distance as the blowing ratio increases from 0.47 to 1.26.     

Vibrations of asymmetric rotors supported by asymmetric bearings

Summary In this paper the vibrations of an asymmetric flexible rotor supported by asymmetric bearings is theoretically analyzed by using Galerkin's method and the perturbation method, and numerically calculated. The effects of the asymmetries of the rotor and the bearings and the changes of the main instability regions and the ultraharmonic resonance due to the external and internal dampings are investigated. The experimental tests are performed on a smaller laboratory model in order to verify the validity of the theoretical results.The following results are obtained; the instability regions divide into two ones by the lack of the symmetries in the rotor and the bearings. The ultraharmonic resonances appear at fractional values of the main critical speed. The character of the internal damping is changed by the magnitude of the asymmetries of the rotor and the bearings.

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Übersicht Es werden die Schwingungen eines unsymmetrischen Rotors in unsymmetrischen Lagern analysiert. Dabei wird sowohl das Galerkin-Verfahren als auch eine Störungs-Methode angewendet. Untersucht werden die durch die Unsymmetrien von Rotor und Lagerung entstehenden Effekte sowie die durch äußere und innere Dämpfung entstehenden Änderungen der wichtigsten Instabilitätsbereiche und der ultraharmonischen Resonanzen. Zur Stützung der theoretischen Ergebnisse wurden Versuche an einem Laboratoriumsmodell durchgeführt.Die wichtigsten Ergebnisse sind folgende: Die Instabilitätsbereiche werden durch die Unsymmetrie von Rotor und Lagerung aufgespalten; ultraharmonische Resonanzen treten bei gebroochenen Werten der Hauptkritischen auf; der Charakter der inneren Dämpfung wird durch die Größe der Unsymmetrien von Rotor und Lagerung verändert.

     

The existence of periodic solutions for nonlinear systems of first-order differential equations at resonance

ＩｎｔｒｏｄｕｃｔｉｏｎａｎｄＰｒｏｂｌｅｍｉｎｔｈｅＲｅｓｅａｒｃｈｏｆＴｏｒｏｉｄＴｈｉｓｐａｐｅｒｄｅａｌｓｗｉｔｈｔｈｅｅｘｉｓｔｅｎｃｅｏｆ2π＿ｐｅｒｉｏｄｉｃｓｏｌｕｔｉｏｎｓｔｏｔｈｅｎｏｎｌｉｎｅａｒｓｙｓｔｅｍｏｆｆｉｒｓｔ＿ｏｒｄｅｒｄｉｆｆｅｒｅｎｔｉａｌｅｑｕａｔｉｏｎｓｗｉｔｈａｄｅｖｉａｔｉｎｇａｒｇｕｍｅｎｔ ｘ(ｔ) =Ｂｘ(ｔ) Ｆ(ｘ(ｔ-τ) ) ｐ(ｔ) ,( 1 )ｗｈｅｒｅｘ(ｔ)∈Ｒ2 , ｘ(ｔ) =ｄｄｔｘ(ｔ) ,τ∈Ｒ ,Ｂ∈Ｒ2×2 ,Ｆ :Ｒ2 →Ｒ2 ｉｓｂｏｕｎｄｅｄａｎｄｐ∈Ｃ(…     

THEORETICAL MODEL OF VIBRATING OBJECT TRANSMITTING NOISE TOWARDS EXTERNAL SOUND

ＩｎｔｒｏｄｕｃｔｉｏｎＶｉｂｒａｔｉｎｇｏｂｊｅｃｔｓｕｎｄｅｒｗａｔｅｒ,ｓｕｃｈａｓｓｕｂｍａｒｉｎｅａｎｄｔｏｒｐｅｄｏ ,ｔｒａｎｓｍｉｔｎｏｉｓｅｔｏｗａｒｄｓｅｘｔｅｒｎａｌｓｏｕｎｄｆｉｅｌｄ ,ｆｏｒｍａｃｈｉｎｅｒｙｖｉｂｒａｔｉｏｎｏｆｉｎｓｉｄｅｐｏｗｅｒａｐｐａｒａｔｕｓ.Ｉｔｗｉｌｌｅｎｈａｎｃｅｇｒｅａｔｌｙｔｈｅｃｏｎｃｅａｌｍｅｎｔｏｆｓｕｂｍａｒｉｎｅａｎｄｔｏｒｐｅｄｏａｎｄｅｎｆｏｒｃｅｆｉｇｈｔｉｎｇｐｏｗｅｒｂｙｃｏｎｔｒｏｌｌｉｎｇｎｏｉｓｅｏｆｓｕｂｍａ…     

Heat transfer and pressure loss of a very shallow fluidized-bed heat exchanger Part 2. Experiment with multirow tube banks

Experiments were carried out on heat transfer and pressure-loss characteristics of a low-pressure-loss fluidized-bed heat exchanger with an extremely small ststic bed height of glass beads. This heat exchanger was composed of a tube bankd in a staggered arrangement and a multislit distributor designed especially to reduce the pressure loss. The effect of the cross-sectional shape of the distributor, the particle size of the glass beads, the static bed height, and the number of rows on heat transfer performance were examined. The heat transfer and pressure-loss characteristics are compared with experimental data in terms of fan power consumption and the compactness of the heat exchanger.     

BOUNDARY ELEMENT METHOD FOR BUCKLING EIGENVALUE PROBLEM AND ITS CONVERGENCE ANALYSIS

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｂｕｃｋｌｉｎｇｅｉｇｅｎｖａｌｕｅｐｒｏｂｌｅｍｈａｓｉｍｐｏｒｔａｎｔｓｉｇｎｉｆｉｃａｎｃｅｉｎｔｈｅｓｔａｂｉｌｉｔｙａｎａｌｙｓｉｓｏｆｅｎｇｉｎｅｅｒｉｎｇｓｔｒｕｃｔｕｒｅ.Ｈｅｎｃｅｔｈｅｎｕｍｅｒｉｃａｌｃａｌｃｕｌａｔｉｏｎｆｏｒｔｈｅｓｅｐｒｏｂｌｅｍｓｉｓｅｘｔｒｅｍｅｌｙｍｅａｎｉｎｇｆｕｌｉｎｃｏｍｐｕｔａｔｉｏｎａｌｍｅｃｈａｎｉｃｓ.ＴｈｅｐｒｅｓｅｎｔｃｏｍｐｕｔａｔｉｏｎａｌｍｅｔｈｏｄｓｆｏｃｕｓｏｎＦＥＭ ,ｄｉｆｆｅｒｅｎｃｅｍ…     

PRELIMINARY ANALYSIS OF SKATING MOTION

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｓｌｅｉｇｈｐｒｏｂｌｅｍｉｓａｃｌａｓｓｉｃｏｎｅｉｎｎｏｎｈｏｌｏｎｏｍｉｃｄｙｎａｍｉｃｓ.ＴｈｅｓｏｌｕｔｉｏｎｓｔｏｔｈｅｐｒｏｂｌｅｍｗｅｒｅｏｂｔａｉｎｅｄｂｙС .А .Чаплыгин( 1 898)ａｎｄＣ .Ｃａｒａｔｈｏｄｏｒｙ( 1 93 3 ) [1].Ｔｈｅｒｅｆｅｒｅｎｃｅ [2 ]ｐｒｅｓｅｎｔｅｄａｆｅｗｑｕｅｓｔｉｏｎａｂｌｅｐｏｉｎｔｓｉｎｔｈｅｓｏｌｕｔｉｏｎｓ .Ａｎｏｔｈｅｒｓｏｌｕｔｉｏｎｗａｓｏｆｆｅｒｅｄｉｎｔｈｅｒｅｆｅｒｅｎｃｅ[3 ] .Ｂｕｔｔｈｅ…     

In-Plane vibration of Timoshenko arcs with variable cross-section

Summary This paper studies in-plane vibrations of Timoshenko arcs with variable cross-section by the transfer matrix approach. For this purpose, the equations governing the in-plane vibration of the arcs are written in a coupled set of first-order differential equations by use of the transfer matrix. Once the transfer matrix has been determined by numerical integration of the equations, the natural frequencies (the eigenvalues) and the mode shapes are calculated in terms of the elements of the matrix for a given set of boundary conditions. This method is applied to arcs with linearly, parabolically and exponentially varying cross-section, and the effects of the varying cross-section and slenderness on the free vibrations of the arcs are studied.

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Übersicht Diese Abhandlung untersucht die ebenen Schwingungen von Timoshenkoskreisbogenträgern mit veränderlichem Querschnitt mit Hilfe einer Transfermatrix-Methode. Zu diesem Zweck werden die linearen Differentialgleichungen, die die ebenen Schwingungen der Kreisbogenträger beherrschen, durch Anwendung einer Transfermatrix umgeschrieben. Sobald die Transfermatrix durch numerische Integration der Gleichungen bestimmt ist, lassen sich die Eigenwerte und Schwingungsformen aus den Matrixelementen für beliebige Randbedingungen berechnen. Diese Methode wird auf die Analyse von Kreisbogenträgern mit linear, parabolisch und exponentiell veränderlichen Querschnitt angewandt. Die Einwirkungen des veränderlichen Querschnittes und der Schlankheit der Kreisbogentr äger auf die freien Schwingungen werden diskutiert.

     

SINGULAR ANALYSIS OF BIFURCATION OF NONLINEAR NORMAL MODES FOR A CLASS OF SYSTEMS WITH DUAL INTERNAL RESONANCES

ＩｎｔｒｏｄｕｃｔｉｏｎＡｎｉｎｔｅｒｅｓｔｉｎｇｆｅａｔｕｒｅｉｎｔｈｅｆｒｅｅｖｉｂｒａｔｉｏｎｏｆａｎｏｎｌｉｎｅａｒｓｙｓｔｅｍｉｓｔｈｅｆａｃｔｔｈａｔｔｈｅｎｕｍｂｅｒｏｆｅｘｉｓｔｉｎｇｎｏｒｍａｌｍｏｄｅｓｍａｙｅｘｃｅｅｄｔｈｅｎｕｍｂｅｒｏｆｄｅｇｒｅｅｓｏｆｆｒｅｅｄｏｍ ,ａｐｈｅｎｏｍｅｎｏｎｎｏｔｅｎｃｏｕｎｔｅｒｅｄｉｎａｌｉｎｅａｒｓｙｓｔｅｍａｎｄｃａｕｓｅｄｂｙｍｏｄｅｂｉｆｕｒｃａｔｉｏｎ .Ｔｈｅｒｅｆｏｒｅｍｕｃｈｗｏｒｋｈａｓｂｅｅｎｄｏｎｅｏｎｔｈｅｓｔ…