This paper considers approximating unsteady aerodynamic forces acting on a plane swept wing in the time domain. Time responses of the aerodynamic forces caused by a step movement of a wing in incompressible flow are calculated by using the time domain vortex element method. It was found that transient characteristics of the step responses associated with a certain generalized aerodynamic force can be represented by one decreasing function regardless of wing motions. By approximating each decreasing function with a set of exponential functions and by calculating apparent mass coefficients and steady state forces, a mathematical model for the aerodynamic forces in the form of 1st-order linear time-invariant differential equations (the state equations) is obtained. The accuracy and the applicability of the method have been confirmed through the comparison between the approximated aerodynamic forces and the unsteady forces calculated directly in the time domain or measured experimentally.
This paper describes the dynamics of liquid driven by capillary force in a tube. The movement of a gas-liquid interface in a horizontal tube as a result of capillary action has been investigated. A theoretical analysis of the interface dynamics is presented where dimensionless numbers representing time and distance scales are introduced, and a unique functional relation is derived. Experiments were carried out with distilled water as the test liquid in glass tubes of inner diameter from 0.5mm to 4.0mm. The position of the gas-liquid interface as a function of time was observed. The experimental results agree well with theory.
The lift on an airfoil flying over a wavy wall surface is calculated using a finite difference method, which was developed by J. Nakamichi to improve LTRAN2 evolved by W. F. Ballhaus and P. M. Goorjian. Numerical computations include cases of a flat plate over a flat solid wall prior to the cases of a moving wavy wall. Modification of grid generating system is the major point for applying the LTRAN2 version to our problem. The weak compressibility (M∞=0.1-0.3) is considered but nonlinearity is neglected in our calculations. The calculated results are compared with those obtained by the lifting surface theory of M. Ichikawa et al. The agreements are quite satisfactory.