Asei Tezuka

Three-dimensional global linear stability analysis of flow around a spheroid

Computational study of flowfields around a spheroid at varied angles of attack is done using Chibas method, which is one of the methods of three-dimensional global linear stability analysis. It is clarified that in the case of a spheroid, nonoscillatory, nonaxisymmetric flow (in the case of zero angle of attack) and nonoscillatory asymmetric flow (in the case of nonzero angle of attack) are observed in a range of the freestream Reynolds number around 4 × 10 3 to 7 × 103, and angle of attack from 0 to 30 deg. The amplification factor of the nonoscillatory asymmetric (or nonaxisymmetric in 0-deg attack angle case) mode is the largest. The transition from nonoscillatory symmetric (or axisymmetric) flow, to nonoscillatory asymmetric (or nonaxisymmetric) flow, occurs when the amplification factor becomes zero. To ascertain the appearance of the nonoscillatory asymmetric flow in an attack angle case, a low-speed wind tunnel experiment was also conducted. The picture of flow visualization shows an asymmetric pattern when the Reynolds number is around 6.5 x 10 3 , whereas the pattern is symmetric at a Reynolds number around 3.5 × 103.

Surface pressure distributions on 4% circular arc airfoil at low Reynolds number

V ERY small aircraft, called micro air vehicles (MAVs), are of high interest because electronic equipment can be miniaturized to allow for the easy manufacture of a vehicle whose entire mass is only a few dozen grams. Small-sized MAVs operate at chord Reynolds numbers below 1:0 10. Because of the influence of viscosity, thin and sharp leading edge airfoils with thickness ratios less than about 5%offer better aerodynamic characteristics than thick and blunt edge airfoils with Reynolds numbers lower than 1:0 10 [1]. Mueller has measured the aerodynamic forces acting on a circular arc airfoil for MAVs; however, compared with thick and blunt edge airfoils, very little literature is available for thin and sharp leading-edge airfoils [1,2], which indicates that more research needs to be done for the low Reynolds number region. Cosyn and Vierendeels [3] numerically studied the low Reynolds number aerodynamics of a flat plate and an S5010 airfoil, which is an airfoil with a 10% thickness ratio. They have also pointed out that low Reynolds number flows exhibit complex flow phenomena, such as laminar separation, which was described by Mueller and DeLurier [4]. For the design and manufacture of MAVs, it is important to know the details of their aerodynamic characteristics, such as surface pressure distribution. However, there is no space inside of the circular arc airfoil for plumbing the pipes from the static pressure port to the pressure transducer. Thus, as far as the authors know, there are no experimental data measuring surface pressure distributions over a circular arc airfoil except for [2], which used luminescent, pressuresensitive paint. In this study, to measure the surface static pressure of the circular arc airfoil, wemade a 4% cambered-airfoil sectionmodel with a 1% thickness ratio by soldering copper pipes. We also conducted surface flow visualizations using the oil flow technique. The present experimental results at a chord Reynolds number of Re 62; 000 are expected to provide useful information for understanding the flowfield of the circular arc airfoil at a low Reynolds number aswell as for confirming the accuracy of numerical estimations concerning a circular arc airfoil.

Laminar Airfoil Modification Attaining Optimum Drag Reduction by Use of Airfoil Morphing

. Aerodynamic characteristics of the baseline and deformed airfoils have been investigated using a viscous–inviscid interaction method. It is shown that the leadingedge deformation is effective in reducing the drag at the offdesign angle of attack, in comparison with the baseline airfoil. The transition point has been estimated, using a numerical method based on a linear stability theory. The deformationisaneffectivemeanstomove thetransition pointaftontheairfoil,andtheextension ofthe laminar flow area results in a reduction in the drag at the offdesign angle of attack. Nomenclature Cd = drag coefficient Cl = lift coefficient Cp = pressure coefficient based on the freestream static and dynamic pressures c = airfoil chord length, m l = girth of the airfoil at the leading edge, m n = amplification factor Rx = Reynolds number based on ue and coordinate along the airfoil surface measured from the leading edge R� = Reynolds number based on ue and � Rec = Reynolds number based on the chord length t = airfoil half-thickness distribution, m U1 = freestream velocity, m=s ue = local velocity at the edge of the boundary layer, m=s x = Cartesian coordinate along the chord direction, measured from the leading edge of the baseline airfoil, m y = Cartesian coordinate perpendicular to x and measured from the leading edge, m ycamber = airfoil camber line, m Z = Cartesian coordinate parallel to x and

Global Stability Analysis of Two-Dimensional Incompressible Flows around an Elliptic Cylinder at Various Incidences

One of the most famous phenomena of transition from steady flow to unsteady flow is the onset of Karman vortices. In this study, the global stability analysis was made to investigate the stability of the flowfield around an elliptic cylinder at various incidences from 0 to 90 degrees. The variation of the critical Reynolds number with the incidence was clarified. The code validation is made by analyzing the critical Reynolds number for the circular cylinder.