Showing papers by "Langley Research Center published in 1972"

Interpolation using surface splines.

Abstract: A surface spline is a mathematical tool for interpolating a function of two variables. It is based upon the small deflection equation of an infinite plate. The surface spline depends upon the solution of a system of linear equations, and thus, will ordinarily require the use of a digital computer. The closed form solution involves no functions more complicated than logarithms, and is easily coded. Several modifications which can be incorporated are discussed.

The maximally achievable accuracy of linear optimal regulators and linear optimal filters

Abstract: A linear system with a quadratic cost function, which is a weighted sum of the integral square regulation error and the integral square input, is considered. What happens to the integral square regulation error as the relative weight of the integral square input reduces to zero is investigated. In other words, what is the maximum accuracy one can achieve when there are no limitations on the input? It turns out that the necessary and sufficient condition for reducing the regulation error to zero is that 1) the number of inputs be at least as large as the number of controlled variables, and 2) the system possess no right-half plane zeros. These results are also "dualized" to the optimal filtering problem.

Microstrip antennas

Abstract: Microstrip antennas consist of a planar resonant radiating element parallel to, but separated, from a ground plane by a thin dielectric substrate ( t \ll \lambda ). These antennas are very thin and consequently rugged and easy to mount. They may be fed from the back through the ground plane or from the edge by depositing microstrip lines on the dielectric substrate. Several varieties of microstrip antennas are discussed in this paper. Design procedures are given for both linearly and circularly polarized antennas. Measured patterns are presented for antennas from UHF through C band.

Remote measurements of the atmosphere using Raman scattering.

Abstract: Raman optical radar measurements of the atmosphere demonstrate that the technique may be used to obtain quantitative measurements of the spatial distribution of individual atmospheric molecular trace constituents (in particular water vapor) and of the major constituents. It is shown that monitoring Raman signals from atmospheric nitrogen aids in interpreting elastic scattering measurements by eliminating attenuation effects. In general, the experimental results show good agreement with independent meteorological measurements. Finally, experimental data are utilized to estimate the Raman backscatter cross section for water vapor excited at 3471.5 A.

Electrostatic-probe measurements of plasma parameters for two reentry flight experiments at 25000 feet per second

Abstract: Unique plasma diagnostic measurements at high altitudes from two geometrically similar blunt body reentry spacecraft using electrostatic probe rakes are presented The probes measured the positive ion density profiles (shape and magnitude) during the two flights The probe measurements were made at eight discrete points (1 cm to 7 cm) from the vehicle surface in the aft flow field of the spacecraft over the altitude range of 853 to 533 km (280,000 to 175,000 ft) with measured densities of 10 to the 8th power to 10 to the 12th power electrons/cu cm, respectively Maximum reentry velocity for each spacecraft was approximately 7620 meters/second (25,000 ft/sec) In the first flight experiment, water was periodically injected into a flow field which was contaminated by ablation products from the spacecraft nose region The nonablative nose of the second spacecraft thereby minimized flow field contamination Comparisons of the probe measured density profiles with theoretical calculations are presented with discussion as to the probable cause of significant disagreement Also discussed are the correlation of probe measurements with vehicle angle of attack motions and the good high altitude agreement between electron densities inferred from the probe measurements, VHF antenna measurements, and microwave reflectometer diagnostic measurements

Spreading of a turbulent disturbance.

Abstract: The presented paper shows the effect of local Mach number on the turbulent disturbance spreading angle relative to the wall and on lateral disturbance spreading angles. Almost all the disturbances angles relative to the wall were determined from investigations where hot-wire contours or hot-film surveys of a 'laminar' boundary layer were obtained. Lateral disturbance spreading angles were obtained from investigations of various conditions including turbulent bursts, reported observations of transverse contamination, and observed transitional flow. It is noted that the disturbance spreading angle relative to the wall seems to remain essentially invariant with Mach number, while the lateral spreading angle decreases sharply with increasing Mach number up to about 6. The good agreement between lateral disturbance spreading angle data and data for the variation of turbulent jet spreading angle with Mach number implies that in the lateral dimension, turbulence in a boundary layer may develop essentially free of wall constraints (similar to a free shear layer).

An actuator extension transformation for a motion simulator and an inverse transformation applying Newton-Raphson's method

Abstract: A set of equations which transform position and angular orientation of the centroid of the payload platform of a six-degree-of-freedom motion simulator into extensions of the simulator's actuators has been derived and is based on a geometrical representation of the system. An iterative scheme, Newton-Raphson's method, has been successfully used in a real time environment in the calculation of the position and angular orientation of the centroid of the payload platform when the magnitude of the actuator extensions is known. Sufficient accuracy is obtained by using only one Newton-Raphson iteration per integration step of the real time environment.

Film-Cooling Effectiveness and Skin Friction in Hypersonic Turbulent Flow

Abstract: Experimental equilibrium temperatures and skin friction at the surface of a flat plate cooled by two-dimensional, tangential slot injection are presented for a Mach 6 mainstream. Effects of slot height, slot mass-flow rate, injection gas temperature, and heat conduction to the slot are investigated. Experimental skin friction and effectiveness data in general agree well with predictions from a finite-difference method. Film cooling at Mach 6 was found significantly more effective than at lower speeds, with large reductions in friction drag measured downstream of the slot These results indicate the necessity for a new evaluation of film-cooling systems for hypersonic vehicles.

Summary of transformation equations and equations of motion used in free flight and wind tunnel data reduction and analysis

Abstract: Basic formulations for developing coordinate transformations and motion equations used with free-flight and wind-tunnel data reduction are presented. The general forms presented include axes transformations that enable transfer back and forth between any of the five axes systems that are encountered in aerodynamic analysis. Equations of motion are presented that enable calculation of motions anywhere in the vicinity of the earth. A bibliography of publications on methods of analyzing flight data is included.

Numerical solutions of the Navier-Stokes equations for the supersonic laminar flow over a two-dimensional compression corner

Abstract: Numerical solutions have been obtained for the supersonic, laminar flow over a two-dimensional compression corner. These solutions were obtained as steady-state solutions to the unsteady Navier-Stokes equations using the finite difference method of Brailovskaya, which has second-order accuracy in the spatial coordinates. Good agreement was obtained between the computed results and wall pressure distributions measured experimentally for Mach numbers of 4 and 6.06, and respective Reynolds numbers, based on free-stream conditions and the distance from the leading edge to the corner. In those calculations, as well as in others, sufficient resolution was obtained to show the streamline pattern in the separation bubble. Upstream boundary conditions to the compression corner flow were provided by numerically solving the unsteady Navier-Stokes equations for the flat plate flow field, beginning at the leading edge. The compression corner flow field was enclosed by a computational boundary with the unknown boundary conditions supplied by extrapolation from internally computed points.

Effects of atmospheric irregularities on sonic-boom propagation.

Abstract: A review is given of information obtained in recent years concerning the effects on sonic-boom signatures of departures of the atmosphere from a perfectly stratified time invariant model. These effects include the observed random variations in boom overpressures from those expected for a stratified atmosphere, the anomalously large and variable rise times, and the occurrence of spiked or rounded waveforms rather than the characteristic N waves. The extent of the variability in data recorded during actual flight tests is summarized in the form of histograms, representing experimentally obtained probability density functions. The physical mechanisms believed to be responsible for the variations and the anomalous features in the signatures are described. These include refraction and subsequent wavefront rippling by turbulence, the possible focusing or defocusing of rays, the formation of caustics, and the phenomenon of wavefront folding, diffraction, and scattering. Recent statistical theories of shock propagation through a turbulent atmosphere proposed by Crow, George and Plotkin, Pierce, Horning, and others are reviewed.

Recent results on the mass, gravitational field and moments of inertia of the moon

Abstract: Doppler tracking data from the Lunar Orbiter series of spacecraft have been used in a more complete analysis of the spherical harmonic coefficients of the lunar gravitational field through thirteenth degree and order. The value obtained for the mass of the Moon,GM = 4902.84 km3 s−2, is in good agreement with previous results and with results obtained by alternate procedures. Acceleration contour plots, derived from the gravitational coefficients, show correlations with surface features on the near side of the Moon, but are of questionable validity for the far side because of the lack of direct tracking data on the far side. Based on the most recent gravitational field data, the current estimate for the polar moment of inertia of the Moon isC/Ma 2 = 0.4019-0.002 +0.004. This value indicates that the interior of the Moon can be homogeneous, but some results presented strongly suggest that the Moon is differentiated, with an excess of mass in the direction toward the Earth.

Asymmetric lateral-directional characteristics of pointed bodies of revolution at high angles of attack

Abstract: A low-speed wind-tunnel investigation was conducted in order to determine the cause of asymmetric yawing moments produced by long pointed fuselage nose shapes at high angles of attack. Force tests were conducted with a cone, tangent-ogive model, and a paraboloid of revolution over a range of Reynolds numbers from 0.15 million to 0.35 million for an angle-of-attack range from 0 deg to 75 deg and an angle-of-sideslip range of plus or minus 30 deg. Tuft and smoke flow-visualization tests were also conducted to aid in the analysis. Large asymmetric yawing moments were obtained for the cone and tangent-ogive body at high angles of attack (of the order of 40 to 60 deg). These large moments were caused by asymmetric shedding of vortex sheets off the long pointed nose. The asymmetric moments could be eliminated by use of symmetrically arranged strikes on the nose. The paraboloid of revolution did not produce a strong asymmetric flow field at high angles of attack and did not exhibit asymmetric moments.

The effect of injection angle on the interaction between sonic secondary jets and a supersonic free stream

Abstract: An experimental investigation, as part of a research program on the development of technology for the design of supersonic combustion ramjets, has been conducted to determine the effect of injection angle on the jet penetration, mixing rate, and airstream total-pressure recovery downstream of five laterally spaced sonic hydrogen jets flush mounted on a flat plate. Results of this investigation indicated that at lower injection angles less free-stream momentum loss was required to turn and accelerate the injected gas downstream and, thereby, less flow disturbance and total-pressure loss were produced. In addition, lower injection angles resulted in improved fuel distribution and faster mixing of the injected gas with the free stream. A correlating parameter, developed from considerations of the effective-momentum-flux differences between the injected gas and the free-stream air, predicted greater penetration and faster mixing for the lower injection angles.

The Inference of Atmospheric Ozone Using Satellite Horizon Measurements in the 1042 cm−1 Band

Abstract: A description and detailed analysis of a technique for inferring atmospheric ozone information from satellite nadir measurements in the 1042 cm band are presented. A method is formulated for computing the emission from the lower boundary under the satellite which circumvents the difficult analytical problems caused by the presence of atmospheric clouds and the watervapor continuum absorption. The inversion equations are expanded in terms of the eigenvectors and eigenvalues of a least-squares-solution matrix, and an analysis is performed to determine the information content of the radiance measurements. Under favorable conditions there are only two pieces of independent information available from the measurements: (1) the total ozone and (2) the altitude of the primary maximum in the ozone profile.

Second derivatives of the flutter velocity and the optimization of aircraft structures.

Abstract: Equations for the second partial derivatives of the eigenvalues of the flutter equation along with the equations for finding the second partial derivatives of the flutter velocity of an aircraft structure with respect to the structural parameters are derived. These partial derivatives are used to develop expressions for the step size in a projected gradient search along a constant mass hyperlane. A projected gradient search along with a gradient mass and a gradient velocity search is used to minimize the mass of a box beam which supports a lifting surface.

A Mixed Optimization Method for Automated Design of Fuselage Structures

Abstract: A procedure for automating the design of transport aircraft fuselage structures has been developed and implemented in the form of an operational program. The structure is designed in two stages. First, an over-all distribution of structural material is obtained by means of optimality criteria to meet strength and displacement constraints. Subsequently, the detailed design of selected rings and panels consisting of skin and stringers is performed by mathematical optimization accounting for a set of realistic design constraints. As a result one obtains a procedure whose practicality and computer efficiency is demonstrated on cylindrical and area-ruled large transport fuselage.

Effect of a circular hole on the buckling of cylindrical shells loaded by axial compression.

Abstract: An experimental and analytical investigation of the effect of a circular hole on the buckling of thin cylindrical shells under axial compression was carried out. The experimental results were obtained from tests performed on seamless electroformed copper shells and Mylar shells with a lap joint seam. These results indicated that the character of the shell buckling was dependent on a parameter which is proportional to the hole radius divided by the square root of the product of the shell radius and thickness. For small values of this parameter, there was no apparent effect of the hole on the buckling load. For slightly larger values of the parameter, the shells still buckled into a general collapse configuration, but the buckling loads were sharply reduced as the parameter increased. For still larger values of the parameter, the buckling loads were further reduced, and the shells buckled into a stable local buckling configuration.

Study of beryllium and beryllium-lithium complexes in single-crystal silicon.

Abstract: When beryllium is thermally diffused into silicon, it gives rise to acceptor levels 191 MeV and 145 meV above the valence band. Quenching and annealing studies indicate that the 145-MeV level is due to a more complex beryllium configuration than the 191-MeV level. When lithium is thermally diffused into a beryllium-doped silicon sample, it produces two acceptor levels at 106 MeV and 81 MeV. Quenching and annealing studies indicate that these levels are due to lithium forming a complex with the defects responsible for the 191-MeV and 145-MeV beryllium levels, respectively. Electrical measurements imply that the lithium impurity ions are physically close to the beryllium impurity atoms. The ground state of the 106-MeV beryllium level is split into two levels, presumably by internal strains. Tentative models are proposed.

Theoretical and measured electron-density distributions for the ram vehicle at high altitudes.

Abstract: Application of a viscous shock-layer analysis to the calculation of nonequilibrium-flow species distributions in the plasma layer of a blunt-nosed vehicle at high altitudes. The theoretical electron-density results obtained are in good agreement with those measured in flight for a hemisphere-9 deg cone entry vehicle. The flight measurements were obtained using electrostatic probes that protruded well into the shock layer. In addition, the theoretically obtained heavy-particle translational temperatures appear to agree fairly well with the electron temperatures that were measured in the flight experiments using voltage-swept thin-wire electrostatic probes. The influence of the reaction rate coefficients on the calculated electron densities has been assessed and shown to be within the uncertainty in the flight data. The theoretical results demonstrate the importance of including in the chemical model the positive ions N2(+), O2(+), N(+), and O(+), in addition to NO(+), for the high altitudes and velocities considered.

A comparison of disturbance levels measured in hypersonic tunnels using a hot-wire anemometer and a pitot pressure probe.

Abstract: Disturbance levels were measured in the test section of a Mach 5 blowdown jet using a constant-current, hot-wire anemometer and a pressure transducer. The disturbance levels, measured by the two instruments and normalized by local mean values, agreed within about 30%, with the pitot data higher than the hot-wire data. The rms disturbance levels measured with the hot-wire anemometer and converted to pitot pressures using a quasi-steady flow analysis, were about two-thirds the levels measured with the pitot probe. The variation of the normalized rms disturbance levels with stagnation pressure indicated that transition occurred in the boundary layer on the nozzle wall and influenced the outputs of the instruments located at the exit of the nozzle when the total pressure was about 35 N/sq cm. Below this pressure the disturbance levels decreased markedly. At higher pressures the disturbances were predominantly aerodynamic noise generated by the turbulent boundary layer on the nozzle wall.

Cone Transitional Boundary-Layer Structure at Me = 14

Abstract: Experimental results suggest that the boundary-layer mean profiles in hypersonic flows may be highly transitional in the outer part of the boundary layer before the transition process is detected at the surface. Means of determining the initial location where the transition process begins in the outer part of the boundary layer are considered.

Shock Interference Bell Aerospace, Heating in Hypersonic Flows

Abstract: A theoretical and experimental study is made of shock interference heating on a variety of basic body shapes and flow conditions. Measurements of pressure and heat transfer are obtained in four wind tunnels at NASA Langley Research Center. These data cover a Mach number range from 6 to 20, and specific heat ratios from 1.20 to 1.67. Peak heating measurements up to 17 times ordinary stagnation point rates and pressure peaks up to 8 times freestream pitot pressure are recorded. Numerical results from computer codes developed for each of the six types of interference compare favorably with most of the experimental data. A theoretical parametric study determined the effects of Mach number, specific heat ratio, and impinging shock strength on amplification of pressure and heat transfer. The results of this study show that a knowledge of heating can be important for the design of hypersonic vehicles such as the space shuttle. The problem is intensified by the fact that the particular type of interference and the location of peak heating regions on the vehicle will vary along the flight trajectory.

Transition in Compressible Free Shear Layers

Abstract: The transition Reynolds number for shear layers produced by interactions between weak and strong shock waves is determined on the basis of experiments performed in a 20-in. (Mach 6) and an 11-in. (Mach 6.9) hypersonic tunnel. A variable angle wedge was used to generate a planar shock wave which interacted with the bow wave of a blunt body. An average value of the transition length (defined as the length along the shear layer from the shock interaction to the point where turbulence became visible on schlieren photographs) was used to determine the transition Reynolds number.

Correlations of Peak Heating in Shock Interference Regions at Hypersonic Speeds

Abstract: Correlations are given of measured pressure and heat-transfer peaks for shock/boundary-layer interactions and shear layer attachment on configurations with both two- and three-dimensional interactions. The peak values were obtained from an investigation of shock interference heating on hemispheres, a 30-deg included angle wedge, and a 2.54-cm-diam cylindrical leading-edge fin model. The investigation covers data for Mach numbers of 6 and 20 over freestream Reynolds numbers ranging from (3.3 to 25.6) million per meter, and specific heat ratios of 1.4 and 1.67.

Procedure for estimating stability and control parameters from flight test data by using maximum likelihood methods employing a real-time digital system

Abstract: A maximum likelihood parameter estimation procedure and program were developed for the extraction of the stability and control derivatives of aircraft from flight test data. Nonlinear six-degree-of-freedom equations describing aircraft dynamics were used to derive sensitivity equations for quasilinearization. The maximum likelihood function with quasilinearization was used to derive the parameter change equations, the covariance matrices for the parameters and measurement noise, and the performance index function. The maximum likelihood estimator was mechanized into an iterative estimation procedure utilizing a real time digital computer and graphic display system. This program was developed for 8 measured state variables and 40 parameters. Test cases were conducted with simulated data for validation of the estimation procedure and program. The program was applied to a V/STOL tilt wing aircraft, a military fighter airplane, and a light single engine airplane. The particular nonlinear equations of motion, derivation of the sensitivity equations, addition of accelerations into the algorithm, operational features of the real time digital system, and test cases are described.

Effects of wind-tunnel disturbances on hypersonic boundary-layer transition. I, II.

Abstract: An experimental investigation of the dependence on facility disturbance of transition on sharp cones has been made. In Part I, the sound radiated from the turbulent boundary layer on the walls of several facilities was measured with pressure transducers mounted flush with the cone surface. In Part II, a constant current hot-wire anemometer measured free-stream and cone shock layer disturbances in two hypersonic helium tunnels. Comparison of hot-wire results with surface pressure measurements in one of the helium tunnels indicate the latter data provide an accurate indication of the facility disturbance levels. Both studies show that transition Reynolds numbers correlate in terms of facility rms sound disturbance levels provided the laminar boundary layers on the models are similar.

Lee-side vortices on delta wings at hypersonic speeds.

Abstract: A fluid-dynamic investigation was carried out to determine the cause of intense heating observed on the lee meridian of hypersonic delta wings and also to derive means for its suppression. Several experimental techniques were combined with analysis of extensive heat-transfer measurements at a freestream Mach number of six in a range of Reynolds number to acquire a general description of the lee-flow structure. With attached leading-edge flow on the delta wings, the dominant feature is a pair of embedded vortices on the lee meridian whose interaction with the boundary-layer is responsible for the observed local heating. On the basis of flow visualization results and heat-transfer correlations, a qualitative vortex flow model is proposed which differs essentially from the conventional inboard separation vortex model.