Showing papers on "Aerodynamic force published in 1983"

Fundamentals of Flight

Abstract: 1 Conversion Factors Between SI Units and English Units 2 Nomenclature 3 A Brief History of Aeronautics 4 The Anatomy of the Airplane 5 The Nature of Aerodynamic Forces: Dimensional Analysis 6 Theory and Experiment Wind Tunnels 7 The Atmosphere 8 Incompressible One-Dimensional Flow 9 One-Dimensional Flow in a Compressible Fluid 10 Two-Dimensional Flow: Lift and Drag 11 The Finite Wing 12 Effects of Viscosity 13 Determination of Total Incompressible Drag 14 Compressibility Drag 15 Airfoils and Wings 16 High-Lift Systems 17 Aerodynamic Performance 18 Stability and Control 19 Propulsion 20 Structures 21 Hypersonic Flow 22 Rocket Trajectories and Orbits Appendix A: Characteristics of the Standard Atmosphere (SI units) Characteristics of the Standard Atmosphere (English Units) Appendix B: Derivation of the Compressible Fluid Bernoulli Equation Appendix C: Summary of State and One-Dimensional Flow Equations Index

Double multiple streamtube model with recent improvements

Abstract: The objective of the present paper is to show the new capabilities of the double multiple streamtube (DMS) model for predicting the aerodynamic loads and performance of the Darrieus vertical-axis turbine. The original DMS model has been improved (DMSV model) by considering the variation in the upwind and downwind induced velocities as a function of the azimuthal angle for each streamtube. A comparison is made of the rotor performance for several blade geometries (parabola, catenary, troposkien, and Sandia shape). A new formulation is given for an approximate troposkien shape by considering the effect of the gravitational field. The effects of three NACA symmetrical profiles, 0012, 0015 and 0018, on the aerodynamic performance of the turbine are shown. Finally, a semiempirical dynamic-stall model has been incorporated and a better approximation obtained for modeling the local aerodynamic forces and performance for a Darrieus rotor.

Friction damping of flutter in gas turbine engine airfoils

Abstract: This paper investigates the feasibility of using blade-to-ground friction dampers to stabilize flutter in blades. The response of an equivalent one mode model in which the aerodynamic force is represented as negative viscous damping is examined to investigate the following issues: the range of amplitudes over which friction damping can stabilize the response, the maximum negative aerodynamic damping that can be stabilized in such a manner, the effect of simultaneous resonant excitation on these stability limits, and the determination of those damper parameters which will be the best for flutter control.

Determination of airplane model structure from flight data using splines and stepwise regression

Abstract: A procedure for the determination of airplane model structure from flight data is presented. The model is based on a polynomial spline representation of the aerodynamic coefficients, and the procedure is implemented by use of a stepwise regression. First, a form of the aerodynamic force and moment coefficients amenable to the utilization of splines is developed. Next, expressions for the splines in one and two variables are introduced. Then the steps in the determination of an aerodynamic model structure and the estimation of parameters are discussed briefly. The focus is on the application to flight data of the techniques developed.

Aeroelastic control flap

Abstract: Auxiliary aeroelastic control flaps arranged on the leading edge of an aircraft's wings at or near the wing tips and ahead of the ailerons for actuation under control of the pilot. The aeroelastic control flaps operate with the ailerons to induce supplementary aerodynamic force to augment the effectiveness of lateral and directional control during high stress manuevers at high dynamic pressures, but do not rely on wing sensors such as accelerometers coupled with a computer for automatic operation.

Correlations between stationary measurable parameters of wing movement and aerodynamic force production in the blowfly ( Calliphora vicina R.-D.)

Abstract: With the aid of a mechanical aerodynamic two component balance, stroboscopes and photographic projections, the following dynamic and kinematic parameters were determined from short periods of stationary flight recorded in tethered blowflies which flew for several hours in a wind tunnel: weight, lift, flight speed, wing-beat frequency, nine angles characteristic for right and left wing-beat positions and a value characterizing the angle of the stroke plane. The data were subjected to a correlation analysis; the total correlation coefficients and the first order partial correlation coefficients were calculated with a significance of 5% and 1% respectively. The correlation between wing-beat frequency and lift was found to be strongly positive. Frequency, lift and flight speed are positively correlated with the sum of the wing-beat angles. Although under the given experimental conditions a significant tendency towards compatible adjustment has been demonstrated lift and thrust can be controlled independently in individual cases. Negative correlations of wing-beat angles of the right and left wing are generally caused by shifting the lower turning points and indicate a neuromotoric counter action of the two wings during turning reactions. A decreasing wing-beat amplitude is often coupled with an increase of the mean stroke plane angle. Numerous other correlations and detailed descriptions are given and compared to functional morphological and neuromotoric data.

Linear/nonlinear behavior in unsteady transonic aerodynamics

Abstract: The accurate calculation of the aerodynamic forces in unsteady transonic flow requires the solution of the nonlinear flow equations. The aeroelastician, on the other hand, seeks to treat his problems (flutter, for example) by means of linear equations whenever possible. He may do this, even when the underlying flow is nonlinear, if the perturbation forces are linear over some (perhaps small) range of unsteady amplitude of motion. This paper assesses the range of parameters over which linear behavior occurs. In particular calculations are made for an NACA 64A006 airfoil oscillating in pitch over a range of amplitudes, frequencies, and Mach numbers. The primary aerodynamic method used is the well known LTRAN2 code of Ballhaus and Goorjian that provides a finite-difference solution to the low frequency, small disturbance, two-dimensional potential flow equation. Comparisons are made with linear subsonic theory, local linearization, and, for steady flow, with the full potential equation code of Bauer, Garabedian, and Korn.

Fluidelastic Instability of an Infinite Double Row of Circular Cylinders Subject to a Uniform Cross-Flow

Abstract: This paper represents the first stage of a fundamental investigation of the vibration phenomena induced in heat exchanger bundles subject to a cross-flow. Using aerodynamic force coefficient data, obtained experimentally from a static wind tunnel model, a linearized quasi-static analysis is employed to analyze the stability of an infinite double row of circular cylinders in uniform cross-flow. From the analysis it is shown that the instability is a result of the negative fluid damping forces, resulting from the complex flow pattern in the row. A new expression is obtained relating the critical velocity for the onset of instability to the damping parameter, the mass parameter and the pitch ratio of the cylinders. The expression is compared with experimental data available in the literature, from dynamic laboratory results, and a good correlation is obtained. Using this stability analysis the effect of mechanical coupling and frequency detuning, both between modes in one cylinder and modes in adjacent cylinders, is examined. In general it is shown that mechanical coupling is destabilizing and frequency detuning stabilizing.

An exploratory study of finite difference grids for transonic unsteady aerodynamics

Abstract: Unsteady aerodynamic forces are calculated by the XTRAN2L finite difference program which solves the complete two dimensional unsteady transonic small perturbation equation. The unsteady forces are obtained using a pulse transfer function technique which assumes the flow field behaves in a locally linear fashion about a mean condition. Forces are calculated for a linear flat plate using the default grids from the LTRAN2-NLR, LTRAN2-HI, and XTRAN3S programs. The forces are compared to the exact theoretical values for flat plate, and grid generated boundary and internal numerical reflections are observed to cause significant errors in the unsteady airloads. Grids are presented that alleviate the reflections while reducing computational time up to fifty-three percent and program size up to twenty-eight percent. Forces are presented for a six percent thick parabolic arc airfoil which demonstrate that the transform technique may be successfully applied to nonlinear transonic flows.

Flutter of Orthotropic Panels in Supersonic Flow Using Affine Transformations

Abstract: Affine transformations are used in analyzing the flutter problem of rectangular simply supported orthotropic panels subjected to supersonic flow over one surface. With the help of certain defined characteristic and bounded quantities a comprehensive solution, which has the isotropic panels solution as a subset, is found to this problem. The physics of this very important aeroelastic problem which has been so obscure for a long time because of the presence of so many parameters is thus clearly exposed by showing how the aerodynamic and the elastic forces interact to produce the panel flutter phenomenon. Both the aerodynamic strip (Ackeret) theory and lifting surface theory are compared and found to agree very well in the analysis. Hence, complete stability boundaries are determined for both flat and buckled panels using the aerodynamic strip theory, the simpler of the two theories.

Nonlinear aerodynamic modeling of flap oscillations in transonic flow - A numerical validation

Abstract: The regime of validity of a nonlinear aerodynamic force and moment formulation, based on concepts from nonlinear functional analysis and applicable to a transonic airfoil with a deflecting flap, is investigated. A time-dependent finite difference technique is used to evaluate the aerodynamic data of the formulation in terms of specified, characteristic motions. Flap-motion histories are generated from the flap inertial equations of motion, with aerodynamic reactions specified by the moment formulation. The motion histories depicting the cases of decaying and growing flap oscillations are compared with histories generated through simultaneous, coupled solution of the fluid-dynamic equations and flap inertial equations of motion. The range of applicability of the formulation is discussed.

A review of preflight estimates of real-gas effects on space shuttle aerodynamic characteristics

Abstract: Preflight estimates of the hypersonic aerodynamic characteristics of the Shuttle orbiter were based on a diverse series of research studies using state of the art techniques developed by basic research in the 60's and 70's. Real-gas viscous calculations on simple shapes that were used to evaluate correlation parameters indicated that real-gas effects reduce aerodynamic forces and moments. Inviscid calculations on winged lifting shapes indicated reduced forces and a slight nose-up pitch resulted because of real-gas effects. Analysis of the extensive wind tunnel data base indicated viscous correlation parameters provided the most appropriate extrapolation technique for estimating flight aerodynamics. Variations because of changes in the ratio of specific heats, which was the only available experimental tool for evaluating real-gas effects, indicated that reduced loads and nose-up pitching moments would occur at high altitudes and Mach numbers but that the values would not exceed the tolerances and variations established about the aerodynamic design data book values derived from viscous correlations. During STS-1, nose-up pitching moments exceeded the established variations.

Transonic Time-Response Analysis of 3-Degree-of-Freedom Conventional and Supercritical Airfoils

Abstract: Aeroelastic time-response analyses are performed for two conventional airfoils, NACA 64A006 and NACA 64A010, and one supercritical airfoil, MBB A-3, in small-disturbance transonic flow. Response results for forces and displacements were obtained by simultaneousl y integrating the structural equations of motion with the unsteady aerodynamic forces computed using two transonic codes: LTRAN2-NLR and USTS. Three-degreesof-freedom—plunge, pitch, and aileron pitch—are considered. Flutter analyses are first performed, with the results used as a guideline for time-response parameter selection. Time-response results are presented showing that for each case the flight speed used to obtain neutrally stable responses is either exactly or nearly the same as the flutter speed determined in the separate flutter analysis. Effect of response amplitudes is investigated. Applicability and limitations of the two transonic codes are evaluated, compared, and discussed. Transonic time-response behavior of these airfoils is physically interpreted and discussed, and comparisons are made.

Aerodynamic atomization of polymeric solutions

Abstract: A helium activated firing device was used to propel viscoelastic fluid slugs (350 cc) to Mach I velocities. Aerodynamic forces disrupt the slug which eventually transforms into a cloud of droplets that fall on the ground below. Various concentrations and types of polymethyl methacrylate (PMM A) in diethylmalonate (DEM) were disseminated. The resultant average drop size for each trial was measured and shown to significantly increase with the addition of polymer. A correlation between average drop size and fluid viscosity was not observed. Both a relative relaxation time deduced from a simple die swell experiment and the first normal stress difference N 1correlated dissemination trials conducted at ambient temperatures. However, only the relative relaxation time correlation was consistent with breakup trials using heated fluids. Use of N 1, for predicting particle size from dissemination tests employing heated viscoelastic fluids can produce considerable error.

Air spoiler for car

Abstract: PURPOSE:To improve brake performance by installing a body installed onto the outside surface of a chassis and an attack-angle adjusting mechanism which increases and reduces the attack angle of the body by a brake signal and setting the resistance and the lift coefficient in high-speed traveling within an optimum range, thus sharply increasing the resistance coefficient on brake application. CONSTITUTION:When a brake pedal 16 is stepped-in by a set amount or less, a body 30 is fixed in the state where the undersurface of the body 30 contacts with the body seat surfaced 31D-33D of the wing spars 31-33, and the forward and downward aerodynamic force is generated at the rear part of a chassis during traveling, and the floating-up due to the lift at the rear part of the chassis is prevented, and driving performance is improved. On brake application where the pedal 16 is stepped-in by a set amount or more, a microswitch 15A is turned ON to put a coil into electric conduction. Then, the contact is set to the position shown by the broken line, and a servo motor 53 is put into electric conduction in the reverse direction and is revolved in the reverse direction, and the rear edge of the body 30 is shifted to the position where a hook 52B contacts with a microswitch 55B. Therefore, the negative angle alpha of attack of the body 3 with respect to air stream increases, and the air stream is exfoliated from the undersurface, and the resistance coefficient increases to apply air brake.

Rotor/body aerodynamic interactions

Abstract: A wind tunnel investigation was conducted in which independent, steady state aerodynamic forces and moments were measured on a 2.24 m diam. two bladed helicopter rotor and on several different bodies. The mutual interaction effects for variations in velocity, thrust, tip-path-plane angle of attack, body angle of attack, rotor/body position, and body geometry were determined. The results show that the body longitudinal aerodynamic characteristics are significantly affected by the presence of a rotor and hub, and that the hub interference may be a major part of such interaction. The effects of the body on the rotor performance are presented.

Control of aeroelastic divergence

Abstract: On forward-swept-wing aircraft, aerodynamic destiffening of the primary wing-bending mode can cause coupling with the short-period mode, potentially resulting in a low-frequency dynamic instability. For a clamped wing this coupled mechanism degenerates into conventional static wing divergence. Studies of a fundamental analytical model of this mechanism show that active control of the clamped wing is possible only through the use of displacement feedback. Control laws for the clamped wing are evaluated and also assessed when body freedom is restored. Additionally, control laws are synthesized directly for a more refined representation of the unrestrained vehicle. Control configured vehicles (CCVs) are not considered.

The effect of handlebar fairings on motorcycle aerodynamics

Abstract: A series of wind tunnel experiments were used to quantify the mean and unsteady aerodynamic forces on a motorcycle fitted with a handlebar fairing and a handlebar windshield. The results have shown that the positive aerodynamic yaw damping of the steerable front frame tends to stabilize wobble mode when a handlebar device is present. The mean front-frame yawing moments as a function of yaw angle were harder to interpret without use of a dynamic simulation. Static arguments were advanced to suggest that cross-wind response may be reduced with a fairing or windshield mounted.

Airfoil shape and thickness effects on transonic airloads and flutter

Abstract: A transient pulse technique is used to obtain harmonic forces from a time-marching solution of the complete unsteady transonic small perturbation potential equation. The unsteady pressures and forces acting on a model of the NACA 64A010 conventional airfoil and the MBB A-3 supercritical airfoil over a range of Mach numbers are examined in detail. Flutter calculations at constant angle of attack show a similar flutter behavior for both airfoils, except for a boundary shift in Mach number associated with corresponding Mach number shift in the unsteady aerodynamic forces. Differences in the static aeroelastic twist behavior for the two airfoils are significant.

Aeroelastic Response of an Aircraft Wing to Random Loads (Reponse Aeroelastique d'une Aile D'Aeronef a des Charges Aleatoires).

Abstract: : A method for the prediction of the response of an elastic wing to random loads at flight conditions using rigid model wind tunnel pressure fluctuation measurements is presented The wing is divided into panels or elements, and the load is computed from measured pressure fluctuations at the centre of each panel A series representation with terms of the correlated noise type is used to curve fit the experimentally determined pressure power spectra Two methods are used to calculate the random load spectrum: a constant correlation approximation, and an exponential spatially decaying cross-power spectrum model for the pressure The coupling between the structural dynamics and aerodynamics of a vibrating wing is taken into consideration using the doublet-lattice method for computing the unsteady aerodynamic forces The acceleration and displacement response spectra have been computed for the F-4E aircraft for various Mach numbers, dynamic pressures and flight altitudes The importance of the unsteady aerodynamic loads induced by the vibration of the wing and input load representation is illustrated by comparing the theoretical predictions with results from flight tests (Author)

Apparent-mass coefficients for isosceles triangles and cross sections formed by two circles

Abstract: In applying inviscid slender-body theory to the calculation of aerodynamic forces on two special types of fuselage, conformal mapping techniques are used to find the exact expressions for the apparent-mass coefficients of their cross sections. The fuselage cross sections considered here either are formed by two circular arcs or have the shape of isosceles triangles. The exact solutions are used to check the applicability of approximating methods using area-equivalence, width-equivalence, and height-equivalence rules. It is found that the areaequivalence rule can hardly be used to estimate the normal forces on all of the cross sections considered in this paper.

Unsteady aerodynamic loading of a tension leg platform

Abstract: A model study has been made of the aerodynamic loads experienced by a typical TLP superstructure. Details are given of extreme quasi-static aerodynamic loads induced under extreme conditions and the aerodynamic admittance function relating the spectrum of drag force to the wind gust spectrum.

Propeller type wind turbine with air stabilizing vane

Abstract: PURPOSE:To enable to operate a wind turbine at the maximum efficiency as against a given speed of wind, by supporting blades in a freely rotatable manner at the boss of a propeller type wind turbine, and changing the pitch angle of the blades by the aerodynamic force acted to an air stabilizing vane fixed to the blades. CONSTITUTION:Support rods 6 are fixed to each blade 5 to project backward with respect to the direction of rotation of the blades 5, i.e., toward the downstream side of wind, and the air stabilizing vane 7 is fixed to the tops of the support rods 6. These vane 7 function like a tail unit of an airplane to the direction W of air flow to hold the assembly of the blade 5 and the vane 7 in a required positional relationship. Here, since arrangement is such that the angle made by the chord line of the blade 5 to the direction W of air flow, i.e., the angle alpha of incidence is equal to an angle alpham at which the lift/drag ratio of the blade becomes maximum, the blade 5 is always turned around the axis O to a position where the efficiency is the maximum.

A study of the aerodynamic interaction between a main rotor and a fuselage

Abstract: The wake of a helicopter rotor can have a significant effect on a fuselage. Results from a recent wind-tunnel investigation show that certain fuselage characteristics, normalized by rotor thrust, scale proportionally to a rotor-wake-induced velocity parameter. Effects on the body of changes in velocity, thrust, tip-path-plane angle of attack, and rotor/body position are discussed. These results show that the rotor can have a favorable or unfavorable influence on the body, depending upon the operating condition.

An aeroelastic analysis of the Darrieus wind turbine

Abstract: The flutter stability of a single Darrieus wind turbine blade spinning in still air is investigated. The blade is modeled as a thin, uniform beam pinned to the rotor shaft, with aerodynamic forces accounted for using strip theory. Eliminating the spatial dependence using cubic B-splines results in a system of algebraic characteristic equations from which the stability of linear motions of the blade at any rotation rate may be inferred. The two most dangerous flutter modes are characterized for a one-parameter family of blades, and the flutter mechanism is shown to be dominated by gyroscopic coupling between motions in the plane of the blade and normal to the plane of the blade.