Showing papers by "National Aerospace Laboratories published in 1993"

Effect of micron-sized roughness on transition in swept-wing flows

Abstract: Boundary-layer transition-to-turbulence studies are conducted in the Arizona State University Unsteady Wind Tunnel on a 45-degree swept airfoil. The pressure gradient is designed so that the initial stability characteristics are purely crossflow-dominated. Flow visualization and hot-wire measurements show that the development of the crossflow vortices is influenced by roughness near the attachment-line. Comparisons of transition location are made between a painted surface, a machine-polished surface, and a hand-polished surface. Then, isolated 6 micron roughness elements are placed near the attachment line on the airfoil surface under conditions of the final polish (0.25 micron rms). These elements amplify a centered stationary crossflow vortex and its neighbors, resulting in localized early transition. The diameter, height, and location of these roughness elements are varied in a systematic manner. Spanwise hot-wire measurements are taken behind the roughness element to document the enhanced vortices. These scans are made at several different chord locations to examine vortex growth.

Systematic error estimation in multisensor fusion systems

Abstract: For multisensor fusion systems it is a prerequisite to accurately estimate and correct all systematic errors. Adequate estimation methods only exist if all systematic errors are constant random variables, while in practice they may change with time. When the object states, the systematic errors and the observations vary according to a linear Gaussian system, then one large Kalman filter forms the optimal estimator for the combined state of all object states and all systematic errors. In general the numerical complexity of this Kalman filter prohibits practical application. In order to improve this situation we decouple the large Kalman filter into a number of separate filters: for each object one track maintenance Kalman filter, and for the estimation of all sensor related systematic errors one Kalman-like filter, which we call the Macro filter. The effectiveness of this approach is illustrated through simulations for a simple example.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Guidance and control law for automatic landing flight experiment of reentry space vehicle

Abstract: An automatic landing flight experiment with a sub-scale model is being prepared for a planned future reentry space vehicle by the National Aerospace Laboratory and the National Space Development Agency of Japan. The sub-scale model is dropped from a helicopter at a 1500m altitude, and, controlled by a n on-board navigation, guidance, and control system, it automatically lands on a lOOOm runway. This paper discusses preliminary study results obtained from numerical simulation by the National Aerospace Laboratory. The guidance and control law was designed using a multiple delay model and multiple design point approach (MDM/MDP). Control system robustness against uncertain and time varying dynamics is especially considered in this approach. The control performances are evaluated with appropriately defined quadratic indices of tracking error. Simple control structures are assumed and parameters are obtained with numerical optimization. The approach was successfully applied to the design, and feasibility of the experiment has been verified with numerical simulations.

Clebsch variable model for unsteady inviscid transonic flow with strong shock waves

Abstract: In comparison with Euler methods unsteady inviscid transonic full potential methods are known to suffer from limitations with respect to the modeling of shock waves. In this paper unsteady 2D and 3D full potential methods are extended with the Clebsch variable model. This model represents exactly the shockgenerated entropy and vorticity. The feasibility of the method is demonstrated for 2D and 3D applications at an overhead of about 10% computational time. Steady and unsteady results of 2D calculations compare favorably with results obtained by Euler methods. In general, the unsteady pressure coefficient distributions in the shock wave trajectories are strongly affected by the improved model.

Flow visualization studies on sidewall effects in two dimensional transonic airfoil testing

Abstract: The effects of sidewall boundary layers in two-dimensional transonic airfoil testing were investigated using oil-flow or liquid crystal visualization techniques. Three different chord models were tested in order to clarify the sidewall effects and to seek a suitable aspect ratio of the airfoil. The oil-flow visualization data systematically reveal the surface flow patterns affected by the sidewalls and suggest a minimum aspect ratio for conducting reliable two-dimensional tests. The results of the liquid crystal visualization also show the three dimensionality of the transition behavior and the necessity of the high aspect ratio. In addition, investigations on effects of the sidewall boundary-layer suction and application of a sidewall interference correction produce significant results for improvement of airfoil testing by removal of the sidewall effects.

View the PDF document PC Based Flight Path Reconstruction Using UD Factorisation Filtering Algorithm .

Abstract: The results of flight path reconstruction using UD factorisation-based Kalman filtering algorithm are presented. The algorithm was implemented using PC-MATLAB functions and validated for simulated as well as real flight data. It is of considerable relevance to analysis of aircraft accident data and general flight data for aerospace vehicles.

A method of wind shear detection for powered-lift STOL aircraft

Abstract: A new wind shear warning system for powered-lift STOL aircraft was evaluated by using a flight simulator. Wind shear warning systems for CTOL aircraft have been designed to detect horizontal shear only. Because the approach air speed of STOL aircraft is lower than that for CTOL aircraft, STOL aircraft are more vulnerable to vertical wind due to (1) a gradient of horizontal shear that is smaller for STOL than for CTOL aircraft because of slower airspeed; (2) STOL aircraft spend longer time in a downdraft; and (3) vertical wind causes a more radical change in the STOL aircraft's flight path because of its lower airspeed. In order to detect the vertical wind, the wind shear warning system proposed calculates the difference between potential flight path measured on-board during shear traversal and trimmed flight path estimated from aircraft status. The most characteristic feature of this new system is that it utilizes only inertial information and pitot-static airspeed data; this yields a convenient means of on-board implementation. Simulation test results confirm that the new system can detect the vertical shear.

Optimal thresholding in wavelet image compression

Abstract: Wavelet transform coding has the potential to offer a lot of benefits with respect to image compression and image filtering as well. The later aspect is of importance in machine processing of high entropy images such as Synthetic Aperture Radar images obtained by the European Remote sensing Satellite (ERS-1). A mathematical model is developed to study the relation between a specified Mean Square Error, the value of the wavelet coefficient threshold and the maximum number of resolutions used. The wavelet compression method is compared with other compression methods like JPEG standard and Vector Quantization for a number of different (in a statistical sense) images amongst others LENA.

The application of an Euler method and a Navier Stokes method to thevortical flow about a delta wing

Abstract: Results :re presented of the numerical simulation of the transonic flow about a 65 deg sharp-edged cropped delta wing ernploying an Euler method as well as a Thin-Layer Navier-Stokes (TLNS) method, both based on a cellcentered central-difference finite-volume scheme. The Euler and TLNS solutions for the configuration at a transonic Mach number of 0.85 are compared in detail with experimental results available from NLR experiments for two incidences, a = 10 deg and a = 15 deg. The viscous flow computations have been performed at a Reynolds number of 9 million, identical to the one of the experiment. employing a slightly adapted form of the algebraic turbulence rnodel of Baldwin and Lomax. Comparison of the computed results and results from the experiment indicate that the Euler method captures the global flow features, i.e. separation from the sharp leading edge, and the formation of the leading-edge and trailingedge vortices, reasonably well except for the still substantial discrepancies in the predicted spanwise pressure distributions. The Navier-Stokes results show a much improved correlation with the experimental data on that point because the method yields, in addition to the flow features already captured by the Euler method, also the boundary layer effects and specifically the secondary separation induced by the leading edge vortex on the wing upper surface.

Study of bubble behavior in weightlessness (effects of thermal gradient and acoustic stationary wave) (M-16)

Abstract: The aim of this experiment is to understand how bubbles behave in a thermal gradient and acoustic stationary wave under microgravity. In microgravity, bubble or bubbles in a liquid will not rise upward as they do on Earth but will rest where they are formed because there exists no gravity-induced buoyancy. We are interested in how bubbles move and in the mechanisms which support the movement. We will try two ways to make bubbles migrate. The first experiment concerns behavior of bubbles in a thermal gradient. It is well known than an effect of surface tension which is masked by gravity on the ground becomes dominant in microgravity. The surface tension on the side of the bubble at a lower temperature is stronger than at a higher temperature. The bubble migrates toward the higher temperature side due to the surface tension difference. The migration speed depends on the so-called Marangoni number, which is a function of the temperature difference, the bubble diameter, liquid viscosity, and thermal diffusivity. At present, some experimental data about migration speeds in liquids with very small Marangoni numbers were obtained in space experiments, but cases of large Marangoni number are rarely obtained. In our experiment a couple of bubbles are to be injected into a cell filled with silicon oil, and the temperature gradient is to be made gradually in the cell by a heater and a cooler. We will be able to determine migration speeds in a very wide range of Marangoni numbers, as well as study interactions between the bubbles. We will observe bubble movements affected by hydrodynamical and thermal interactions, the two kinds of interactions which occur simultaneously. These observation data will be useful for analyzing the interactions as well as understanding the behavior of particles or drops in materials processing. The second experiment concerns bubble movement in an acoustic stationary wave. It is known that a bubble in a stationary wave moves toward the node or the loop according to whether its diameter is larger or smaller than that of the main resonant radius. In our experiment fine bubbles will be observed to move according to an acoustic field formed in a cylindrical cell. The existence of bubbles varies the acoustic speed, and the interactive force between bubbles will make the bubble behavior collective and complicated. This experiment will be very useful to development of bubble removable technology as well as to the understanding of bubble behavior.

Vortex simulation of turbulent mixing layers

Abstract: We present here a brief survey of vortex-dynamical simulations of the plane mixing layer using different forms of vortex elements. Points and blobs, which have been widely used in the past, suffer from irregular evolution of the vortex sheet approximating the shear layer, and the rather long time-averaging required to obtain meaningful statistics. A technique recently proposed by the authors, using vortex arcs or sheet elements, has been found to be helpful in avoiding these difficulties. In particular, this technique avoids the singularity in induced velocity associated with point vortex techniques, and is therefore in no need of any form of the “desingularization” that is often introduced in the latter. New results for excited mixing layers using the vortex sheet element model are presented, and are shown to be in good agreement with experimental observations.

End-to-end delay reduction in narrow bandwidth real-time multimedia tele-education applications

Abstract: The transmission of multimedia page sequences in real-time tele-education presentations via narrowband linksresults in unacceptable end-to-end delays This paper proposes a time-shifting method referred to as pretransferwhich transfers presentation data in background during the session, without user involvement Point-to-point and multipoint protocols are discussed For multicast situations an effective page-scheduling method is developed1 INTRODUCTION Real-time tele-education by means of multimedia technology enables universities to extend their educationalfacilities to 'remote' students Using standard PC networks and equipment to implement multimedia terminalsoffers the possibility to produce and control educational materials in a cost-effective way The teacher usuallysupports his lecture by a number of 'screens' or 'pages', prepared in advance These may indeed resemble corn-pound pages, ie consisting of various data types like graphical and text objects, pictures, scanned overheads,animations and even audio or video-tracks During the session these pages are presented in a way similar to aconventional presentation of overhead sheets or slides as in use with face-to-face education Moreover, the teacheris able to add or correct the presented items on-line Beside the processing and transmission of these types of infor-mation, a tele-education systern should provide two-way audio communication and in certain situations even

NASA/DoD Aerospace Knowledge Diffusion Research Project. XXXIII - Technical communications practices and the use of information technologies as reported by Dutch and U.S. aerospace engineers

Abstract: As part of Phase 4 of the NASA/DOD Aerospace Knowledge Diffusion Research Project, two studies were conducted that investigated the technical communications practices of Dutch and U.S. aerospace engineers and scientists. A self-administered questionnaire was distributed to aerospace engineers and scientists at the National Aerospace Laboratory (The Netherlands), and NASA ARC (U.S.), and NASA LaRC (U.S.). This paper presents responses of the Dutch and U.S. participants to selected questions concerning four of the seven project objectives: determining the importance of technical communications to aerospace engineering professionals, investigating the production of technical communications, examining the use and importance of computer and information technology, and exploring the use of electronic networks.

Estimation of neutral and maneuver point of aircraft by dynamic maneuvers

Abstract: The Neural point (N[o]) and Maneuver point (N[m]) are important longitudinal stability parameters which critically determine the Aft CG limit of an aircraft. Since these parameters are a function of speed, angle of attack, external store configuration, control surface deployment(slats) etc., extensive flight tests are conducted to accurately deEermine these critical stability parameters. Exisiting methods based on steady state trim flights turn out to be time consuming and are error prone due to the results being dependent on air data and aircraft weight data. In this present report an alternative flight test methodology, based on dynamic maneuver followed by modern aircraft parameter estimation analysis method is proposed to determine N[0] and N[m] simultaneous1y. This results in substantial reduction of flight test time. Further the estimation of stability parameters are independent of air data, mass or inertia data of the aircraft and depend only on the accuracy of CG position of the aircraft and the accuracy of inertial sensors (pitch rate and normal accelerations).

The fluid mechanics of phase change

Abstract: The phenomena of evaporation and condensation are subject to the laws of fluid mechanics. While the usual continuum equations hold in the bulk of the vapour, the exchange processes near the interfaces have to be modelled more accurately by the laws of molecular dynamics. When an inert gas is present, the mass fluxes are diffusion-controlled and tend to be small; the fluxes are much greater in the kinetic-controlled pure vapour case. Strange phenomena, namely, jumps in the temperature and possible inversion in the temperature field, are predicted by the theory for the pure vapour case. While the jumps have been found experimentally, the whole phenomenon has yet to be fully understood and remains an interesting field for fluid mechanical investigations.