Calculations Showing the Influence of Aerodynamic Damping on Binary Wing Flutter
The influence of damping is examined by comparing the flutter critical speeds and frequencies obtained using the complete equations of motion and those obtained when all the damping terms are omitted. The calculations are made for binary flexure-torsion flutter of a wing in incompressible flow and the comparisons extend over ranges of values of the principal parameters. When the ratio of air density to wing density is high, the damping terms are found to raise the flutter speed by a large amount. But when the ratio of air density to wing density is low, a condition often occurring in practice, it appears that, over a wide range of parameter variation, the flutter speed obtained in the absence of damping is reasonably close to that obtained from the complete equations. Further experience is obviously needed before any general conclusions can be re~¢hed, but the present results offer some hope of reducing either the extent of, or the accuracy needed in, the aerodynamic information used for wing flutter calculations. It is pointed out that with constant aerodynamic coefficients the flutter speed for an undamped system is independent of the wing density.
Some general considerations concerning the destabilizing effect in nonconservative systems
ZusammenfassungEs wird ein lineares System mitN Freiheitsgraden untersucht, beansprucht durch eine Gruppe nichtkonservativer Kräfte, welche linear von den verallgemeinerten Koordinaten abhängen. Mehrere Sätze bezüglich die labilisierende Wirkung von kleinen Kräften, die von den verallgemeinerten Geschwindigkeiten abhängen, werden aufgestellt. Diese Kräfte können von der Dämpfung oder von gyroskopischen Einflüssen herrühren.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.