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A number of studies have examined the potential efficacy of global flow rate and edge rate for specifying changes in self-motion. These have ranged from passive judgements of simulated accelerating self-motion to the active control of altitude in the presence of changes in flow and edge rates. A number of these studies are summarized and an attempt is made to reconcile their respective findings.
Systematic experimental studies were performed to establish the aerodynamic impact of very small leading-edge simulated ice (roughness) formations on lifting surfaces. The geometries studied include single element configurations (airfoil and 3-D tail) as well as multi-element high-lift airfoil geometries. Emphasis in these studies was placed on obtaining results at high Reynolds numbers to insure the applicability of the findings to full-scale situations. It was found that the well-known Brumby correlation for the adverse lift impact of discrete roughness elements at the leading edge is not appropriate for cases representative of initial ice build up (i.e., distributed roughness). It was also found that allowing initial ice formations of a size required for removal by presently proposed deicing systems could lead to maximum lift losses of approximately 40 percent for single-element airfoils. Losses in angle-of-attack margin to stall are equally substantial - as high as 6 degrees. Percentage losses for multi-element airfoils are not as severe as for single-element configurations, but degradations of the angle-of-attack-to-stall margin are the same for both.
Boundary-layer receptivity in the leading edge region for bodies with blunt leading edges is investigated in this research program. Receptivity theory provides the link between the unsteady disturbance environment in the freestream and the initial amplitudes of instability waves in the boundary layer. This is a critical problem which must be addressed in order to develop more accurate prediction methods for boundary-layer transition.
Edge enhancement of an input image by four-wave mixing a first write beam with a second write beam in a photorefractive crystal, GaAs, was achieved for VanderLugt optical correlation with an edge enhanced reference image by optimizing the power ratio of a second write beam to the first write beam (70:1) and optimizing the power ratio of a read beam, which carries the reference image to the first write beam (100:701). Liquid crystal TV panels are employed as spatial light modulators to change the input and reference images in real time.
Results are presented, at a resolution of 20 arcsec, of observations of the distribution of radio continuum intensity and linear polarization with the VLA in two nearby edge-on spiral galaxies, NGC 891 and NGC 4565, at 6 and 20 cm, respectively. A unified model is presented to account for the main features of the radio polarization in these two galaxies. The model geometry is determined from recent observations of face-on galaxies where the polarized emission is found to be strongest in the dark inter-arm and outer parts of the disks. A substantial Z-thickness is ascribed to this polarized emission. It is shown that the exceptionally strong wavelength dependence of this type of Faraday depolarization can result in edge-on galaxies becoming rapidly 'Faraday thick' at decimeter wavelengths, thereby obliterating the polarization from regions on the dark side of the disk. The degree of polarization observed in both galaxies increases strongly with increasing Z-distance from the plane.
The flow around blunt trailing edge airfoils was studied by solving the Reynolds-averaged Navier-Stokes equations. The solution procedure combines a grid around the airfoil with a second grid for the wake so that the time advancement over the domain is fully implicit. This is not only very efficient for the algorithm but also allows implicit solutions of a one equation turbulence model appropriate for both boundary layers and wakes. An algebraic and two one-equation turbulence models are tested for a blunt RAE 2822 airfoil section and detailed comparisons with experimental data are presented in the trailing edge region.
A mechanically operated leading edge flap system was used to perturb leading edge vortex position on a free-to-roll double-delta wing. The motion of the flaps was synchronized with the wing rolling oscillations and the effect of the phase shift between the oscillations of the wing and the flaps was investigated. Experimental results indicated that this simple approach was effective in reducing the amplitude of the unintended rolling motion and its implementation to actual airplane configurations is rather simple.
A finite element thermoviscoplastic analysis method, which employs a unified constitutive model proposed by Bodner and Partom, is used to predict rate-dependent nonlinear structural behavior. The method is evaluated by predicting stress-strain behavior of a uniaxially loaded bar of nickel-based superalloy (B1900 + Hf) material. The method is used to predict the time-dependent thermoviscoplastic response of a B1900 + Hf leading edge subjected to oscillating shock-shock interaction loading. Viscoplastic analysis shows that the leading edge experiences significant plastic straining. The plastic region increases with cyclic loading in the high heat flux area.
An experimental study of the generation of Tollmien-Schlichting waves and wave packets in a flat-plate boundary-layer by weak freestream turbulence has been conducted with the intent of clarifying receptivity mechanisms. Emphasis was placed upon the properties of such waves at stations as far forward as the minimum critical Reynolds number. It was found that alteration of the flow about the leading edge, due either to an asymmetry associated with lift, or due to a change of the fineness ratio of the leading edge, altered the T-S wave amplitude at early stations. The subsequent growth of the waves proceeded faster than expected according to certain stability theory results. Speculation regarding receptivity mechanisms is made.
The separation bubble formed on an airfoil at low Reynolds number behind a simulated leading-edge glaze ice accretion is studied experimentally. Surface pressure and split hot-film measurements as well as flow visualization studies of the bubble reattachment point are reported. The simulated ice generates an adverse pressure gradient that causes a laminar separation bubble of the long bubble type to form. The boundary layer separates at a location on the ice accretion that is independent of angle of attack and reattaches at a downstream location 5-40 percent chord behind the leading edge, depending on the angle of attack. Velocity profiles show a large region of reverse flow that extends up from the airfoil surface as much as 2.5 percent chord. After reattachment, a thick distorted turbulent boundary layer exists. The separation bubble growth and reattachment are clearly seen in the plots of boundary-layer momentum thickness vs surface distance. Local minima and maxima in the boundary-layer momentum thickness development compare well with the shear layer transition point as indicated by the surface pressures and the reattachment point as measured from surface oil flow, respectively.
The effect of a thin tangential jet located at the leading edge of the wing of a tilt rotor configuration in hover is computed using the thin-layer Navier-stokes equations. Computations showed that leading edge tangential blowing is effective in reducing the download caused by the impingement of the rotor download caused by the impingement of the rotor downwash on the wing. Results from the numerical model support previous experimental findings that download reduction is due mainly to a decrease in upper surface pressure and not an increase in pressure on the lower surface. The numerical solution clearly shows that because of the three-dimensionality of the flow field, the download could be reduced further by allowing a spanwise variation in blowing strength.
Model atmosphere calculations of the spectrum of a neutron star cooling after an X-ray burst show that the photoelectric edge of iron should be prominent. No clear evidence for such a redshifted feature in the spectrum of a burst from X1636 - 53 is found, and it is concluded that the iron abundance there must be less than 0.3 solar. Unless the iron abundance of the surface matter on the neutron star is highly time-dependent, the present result argues against the 4.1-keV absorption line seen in some bursts from X1636 - 53 by Waki et al. (1984) being due to iron. The iron edge will be a powerful diagnostic of the surface redshift of the neutron star in burst sources where the iron abundance is more nearly solar.
An edge-emitting monolithically integrated master oscillator power amplifier (M-MOPA) has been fabricated by integrating a distributed Bragg reflector laser with a 500 microns long single mode amplifier. The M-MOPA contains a strained InGaAs quantum well in the active region and operates at about 981.5 nm in an edge-emitting fashion with maximum powers in excess of 175 mW. Single longitudinal and transverse mode operation is maintained to powers in excess of 110 mW CW.
Superconductor/normal-conductor/superconductor (SNS) devices in which electronically active layers consist solely of materials in Y/Ba/Cu/O system fabricated in edge geometry. Made of different materials described in "SNS Device Made With Edge-Defined Geometry" (NPO-18303). Advantages include desirable electrical characteristics and less difficulty in fabrication. Attractive for development into high-frequency oscillators, magnetic-field sensors, and submillimeter-wave mixers.
This report discusses progress made on NASA Cooperative Agreement NCC2-545, 'An Experimental Study of a Turbulent Boundary Layer in the Trailing-Edge Region of a Circulation-Control Airfoil' during the period 9/1/91 through 9/30/92. The study features 2-component laser Doppler velocimeter (LDV) measurements in the trailing edge and wake regions of a generic 2-dimensional circulation-control model. The final experimental phase of the study will be carried out in the Ames High Reynolds Number Channel 2 (HRC2) transonic blow-down-facility. During the 13-month period covered by this report, work continued on the development of the near-wall laser Doppler velocimeter (LDV) described in previous reports.
A numerical analysis of the flowfield characteristics and the performance degradation of an airfoil with leading edge ice accretions was performed. The important fluid dynamic processes were identified and calculated. Among these were the leading edge separation bubble at low angles of attack, complete separation on the low pressure surface resulting in premature shell, drag rise due to the ice shape, and the effects of angle of attack on the separated flow field. Comparisons to experimental results were conducted to confirm these calculations. A computer code which solves the Navier-Stokes equations in two dimensions, ARC2D, was used to perform the calculations. A Modified Mixing Length turbulence model was developed to produce grids for several ice shape and airfoil combinations. Results indicate that the ability to predict overall performance characteristics, such as lift and drag, at low angles of attack is excellent. Transition location is important for accurately determining separation bubble shape. Details of the flowfield in and downstream of the separated regions requires some modifications. Calculations for the stalled airfoil indicate periodic shedding of vorticity that was generated aft of the ice accretion. Time averaged pressure values produce results which compare favorably with experimental information. A turbulence model which accounts for the history effects in the flow may be justified.
We are completing a project designed to realistically assess the global/cosmological significance of superwinds by attempting to systematize our understanding of them (determine their incidence rate and the dependence of their properties on the star-formation that drives them). Specifically, we are analyzing data from an optical spectroscopic and narrow-band imaging survey of an infrared flux-limited sample of about 50 starburst galaxies whose stellar disks are viewed nearly edge-on. This edge-on orientation is crucial because the relevant properties of the superwind can be far more easily measured when the flow is seen in isolation against the sky rather than projected onto the much brighter gas associated with the starburst galaxy itself.
A procedure is developed for the numerical simulation of stagnation-free inviscid supersonic and hypersonic flows about waveriders with sharp leading edges. The numerical approach involves the development of a specialized grid generator (named HYGRID), an algebraic solution-adaptive grid scheme, and a modified flow solving method. A comparison of the results obtained for several waverider geometries with exact solutions, other numerical solutions, and experimental results demonstrated the ability of the new procedure to produce stagnation-free Euler solutions about sharp-edged configurations and to describe the physics of the flow in these regions.