Effect of strakes on the autorotational characteristics of noncircular cylinders

Abstract

An experimental investigation is conducted to evaluate the effects of windward strakes on the autorotational characteristics of a typical noncircular cylinder. The results indicate that autorotational speeds are very sensitive to strake height and, more particularly, to their location. Reductions in autorotational speeds by as much as 75% were obtained for a strake height of h/b$ = 0.3 located at r/b Q = 0.2. Exploratory two-dimensional pressure measurements indicated that the strakes themselves develop significant, pro-or antiautorotational side forces depending on their location. A strip theory analysis showed that a reduction in ^c/ is mainly responsible for this phenomenon. -yO ys2 h t *i 'i N P r V a. P Nomenclature = width of the model = moment coefficient about axis of rotation, = moment/ Vip V 2 b 0 f = pressure coefficient, = (p -p^ )/ l /2p V 2 -sectional side force coefficient, = side force per unit length/ VtpV^bQ = sectional side force coefficient of the basic crosssectional shape only = maximum positive value of C y -net side force on strake assembly, C ysl + C ys2 = side force coefficient of left strake = side force coefficient of right strake = strake height = length of the autorotation model = axial distance between the leading edge of the autorotation model and its center of gravity =v/ = axial distance between the center of gravity and trailing edge of the autorotation model = V* = moment about axis of rotation = pressure = distance measured along the bottom surface from corner to strake location (Fig. 3) = coordinate measured from center of gravity along autorotation model axis (Fig. Al) = freestream velocity = angle of attack = density of air = cross-flow angle = value of <t > when C y = autorotational speed angular velocity Subscript oo = freestream

Control of autorotational characteristics of light-airplane fuselages

“…In Ref. 6, detailed two-dimensional (crossflow) pressure tests over the noncircular section of model A were carried out with several strake configurations. Similar two-dimensional pressure distribution tests for model B were carried out in Ref.…”

“…In Ref. 6, the effect of strakes on the autorotational characteristics of a sharp-cornered, noncircular cylinder at low speeds and low Reynolds number was systematically investigated through single-degree-of-freedom, free-to-roll autorotational tests and pressure measurements on the corresponding twodimensional cylinder in crossflow. The results of this study indicated that the autorotational speeds are very sensitive to strake height and their location on the underside.…”

Estudio experimental del efecto Magnus en cuerpos cilíndricos de secciones transversales diversas

“…Se han realizado estudios de cuerpos no cilíndricos circulares con aletas [17] sometidos a una corriente libre y se ha estudiado el efecto de autorrotación en función de la posición y geometría de dichas aletas. Dichos estudios experimentales han permitido determinar los patrones de flujo para diferentes ángulos de inclinación del cuerpo ensayado y la distribución de presiones alrededor del mismo.…”