An experimental determination of dynamic coefficients for the Basic Finner missile by means of the angular dynamic balance

Equipment developed in this Laboratory permits the determination of eight of the dynamic coefficients useful in describing the force and moment reactions on a submerged body moving in water. These coefficients comprise the partial derivatives of moment (about the yaw axis) and of force (in the horizontal plane, and perpendicular to the longitudinal axis) with respect to velocity and acceleration components in specified directions. So long as the instantaneous angles of attack are small and scale effects are absent, these coefficients have constant values. A complete list of coefficients is given in Ref. (1), as are definitions, sign conventions and formulas for making the coefficients nondimensional. The eight coefficients tabulated below are those pertinent to lateral translation and rotation about the yaw axis for a body of revolution: Nr' coefficient of rotary moment derivative Nr[dot]' virtual moment of inertia coefficient (angular acceleration) Nv' coefficient of static moment derivative Nv[dot]' virtual moment of inertia coefficient (lateral acceleration) Yr' coefficient of rotary force derivative Yr[dot]' virtual inertia coefficient (angular acceleration) Yv' coefficient of static force derivative Yv[dot]' virtual inertia coefficient (lateral acceleration) where the prime indicates that the coefficients are in dimensionless form. It is the purpose of the experimental program undertaken at this Laboratory to determine the numerical values of the above quantities for the Basic Finner missile (Fig. 1). Because of the required differences in the experimental methods, however, the program was divided into two parts. This report deals only with Part 1, and is restricted to the following quantities: Nr[dot]', Nv', Yr[dot]', Yv', and the linear combinations Nr' - Nv[dot]' and Yr' - Yv[dot]'. Remaining quantities will be the subject of another report

Superventilated flow past delta wings

Although delta wings have been known for some time in aeronautics (1)(2) their introduction into a hydrodynamic context has been quite recent. As in the flow of air, the delta wing provides a simple but useful configuration for investigating three-dimensional problems in cavity flows. At the start of the present work (1960), only one theoretical study on this subject was known (3). No information on flow patterns, force characteristics or other properties were available for these shapes. It was accordingly decided to embark on an experimental program with the aim of providing the basic characteristics of the cavitating flow past delta wings, to observe and outline any interesting features of these flows and, finally, to provide a physical basis for any mathematical analysis of the flow that might be undertaken. Measurements of lift, drag and pitching moment and pressure distributions were made on a family of simple flat plate delta shapes of varying apex angle; several configurations outside this family were also tested. These included a diamond plan form, reverse delta, and a delta with a 90 degree bottom. All were without camber and were tested with no yaw angle. After completion of this work, the exhaustive treatment of Reichardt and Sattler (4) appeared which also deals with cavitating delta wings. It is believed, however, that the current report and that of Reichardt are sufficiently different in scope and method to justify the presentation of the present results

A Preliminary Experimental Study of Vertical Hydrofoils of Low Aspect Ratio Piercing a Water Surface

Most types of problems which arise in connection with the use of a hydrofoil operating in water can be solved simply by treating it as an airfoil operating in air. For this purpose, use can be made of the great wealth of theoretical information and experimental data which can be found in the literature. There are, however, regimes of operation of the hydrofoil which are not duplicated by the airfoil excepting possibly under very special conditions. These regimes are identified by one of the following: (a) cavitation (b) ventilation (c) proximity to a free surface Cavitation is characterized by the presence of water vapor bubbles at regions in the flow where the pressure is less than the vapor pressure corresponding to the existing water temperature. Although most commonly observed on the blades of propellers or on the vanes of axial flow pumps, cavitation can also be present on fins used to stabilize high speed underwater missiles, on hydrofoils used as lifting surfaces, or on support struts of various kinds. Allied to this problem is ventilation, a condition which is like cavitation in that it results in discontinuities in density in the fluid surrounding the hydrofoil, although the initiating mechanism is fundamentally different and the lighter medium is air or gas instead of water vapor. A third type of flow regime which may be very important is that associated with a hydrofoil which approaches or intersects a water-vapor or water-gas interface. In this case the flow must satisfy the constant pressure boundary condition on that interface. The effect of gravity may or may not be important, and the hydrofoil can be oriented in any direction. A lifting hydrofoil would most likely be parallel, or nearly parallel, to the water surface, whereas a support strut or a stabilizing fin would inter sect the water surface nearly at right angles. It is this last mentioned type of ope ration which is investigated in this report, and which, as will be seen later, also implies a study of the effects of air ventilation. Among the specific fundamental questions which arise in considering a vertical hydrofoil piercing a flat water surface and which is at an angle of attack to the flow, are the following: (a) How does the presence of the air-water interface affect the apparent aspect ratio of the hydrofoil as compared with its geometrical value? (b) What is the effect of air ventilation on the value of cross-force developed by the hydrofoil, and what observations can be made regarding the inception of this phenomenon? Since no previous hydrofoil studies had been performed in the Free Surface Water Tunnel, it was also of interest to determine the suitability of that facility and its associated equipment for doing work of this kind. On the other hand, the investigation was intended only as a preliminary one and was, therefore, undertaken with limited resources

An Experimental Determination of Dynamics Coefficients for the Basic Finner Missile By Means of the Translational Dynamic Balance

Report number E -73.3, published by this Laboratory in June 1957, (Ref. 1) presents certain dynamic coefficients for a model of the Basic Finner Missile (Fig. 1) which had been measured on the angular dynamic balance in the High Speed Water Tunnel at this Laboratory. Several of the desired coefficients, specifically Y_r' coefficient of rotary force derivative Y_v' virtual inertia coefficient (lateral acceleration) N_r' coefficient of rotary moment derivative N_v' virtual moment of inertia coefficient (lateral acceleration) remained undetermined at that time. By employing the translational dynamic balance and its associated internal moment balance, it had been hoped that the missing values for these coefficients would be supplied. Only partial success has been achieved, insofar as numerical results are concerned, at contract expiration time. The coefficient of static force derivative, Y_v', and the virtual inertia coefficient, Y_v', have been measured as part of this investigation. These coefficients have been designated Z_w' and Z_ẇ' in this report to comply with the new direction of model motion with respect to the tunnel coordinate system. Since the first of these, Z_w', had already been determined in the angular dynamic measurements, only the presentation of a value for Z_ẇ' is new. This coefficient had appeared in linear combination with the coefficient of rotary force derivative; hence the latter important quantity also is now uniquely determined. In addition to the force reactions, the moments arising from transverse velocity and acceleration components were also measured, but under conditions of undetermined deflection of the model-spindle assembly. For this reason the moment coefficients have not been presented here, nor have the experimental procedures used to obtain them been included. Instead, a detailed discussion of both the apparatus and the experimental procedures has been planned for reference 3

Dynamic Coefficients of the MK-13 Torpedo

The forces and moments which act on a submerged body undergoing unsteady motion can be described in terms of selected dimensionless constant hydrodynamic coefficients if the instantaneous angles of attack are kept small. To determine the values of these coefficients a model of the body can be supported from the spindle of a dynamic balance (1) in the flowing stream of a water tunnel working section. This procedure was carried out for certain coefficients on a 2-inch diameter model of the Mk-13 torpedo (Fig. 1) using the Angular Dynamic Balance in conjunction with the High Speed Water Tunnel at the California Institute of Technology, Hydrodynamics Laboratory

A laboratory experiment on simulated wave-riding dolphins

[no abstract

Summary of Reports and Publications Issued on Contract N6onr-24424

This memorandum is to list technical reports prepared under Contract No. N6onr-24424 during its life, which extended from April 1, 1949 through April 30, 1954. As may be seen from the report titles listed below, the research dealt almost exclusively with the dynamics of underwater bodies running in open cavities. A major portion of the work dealt with the basic hydrodynamics of this type of flow, and hence was unclassified. However, part of the work which dealt with some of the more specialized aspects of the problem was, of necessity, classified. In all, eight unclassified reports and five classified reports were prepared. Mr. J. P. O'Neill was in charge of the studies during the active life of the project, and, as may be seen from the report authors, he was ably assisted by several active workers, principal among whom were the following: Messrs. Byrne Perry, Taras Kiceniuk, W. M. Swanson and Dr. E. Y. Hsu

Simulated Wave-Riding Dolphins

The explanation of the mechanism by which dolphins are able to ride bow waves of ships, or natural surf and wind-generated waves, has stimulated much discussion and controversy. Since an excellent summary of previous research on the wave-riding problem has been given by Fejer and Backus, only a few remarks by way of review will be given here