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Viewing 70801 to 70830 of 107816
1990-09-01
Technical Paper
901856
S. W. Singer, E. A. Mattson
A computational method based on a cell-centered, finite-volume spatial discretization and explicit time-stepping algorithm for solving the Euler and Navier-Stokes equations is used to simulate inviscid and viscous flow about configurations including a diverging nozzle, a 74 degree delta wing, and a Mach 6 Waverider. Solutions are obtained using patched multizone grids with both matching and different grid densities across zonal interfaces and are correlated with analytical solutions and experimental data. The computational results increase the confidence in applying Euler and Navier-Stokes solvers to the more complex mixed internal/external flows associated with complete aircraft configurations.
1990-09-01
Technical Paper
901855
Dong-Ho Lee, Oh-Hyun Rho, Chang-Joo Kim
A fast explicit multi-grid scheme proposed by NI has been applied to steady transonic flows around eight bladed SR-3 advanced turbo-prop. FVI(Finite Volume Integral) used in one step distribution formula was implemented more easily by representing Euler equations in cartesian coordinate system. One step distribution formula obtained from Lax-Wendroff type differencing were used only for coarse grid calculations without FVI, so the increase in computational work per iteration was about only 10% compared with 25% in full approximation scheme. And by using standard coarsening and straight injecton for restriction, no additional memory was needed. Artificial viscosity and boundary conditions were applied only in the finest grid level, so the efficiency of multi-grid scheme was nearly independent of them. About 60% saving in computing time was obtained with 4 levels of coarse grid.
1990-09-01
Technical Paper
901854
G. A. Miller, S. Agrawal
A computational analysis of the external flowfield about a fighter configuration was conducted to evaluate an Euler solver and to investigate a hybrid combination of an Euler solver and a panel method. The analysis demonstrated the usefulness of Computational Fluid Dynamics (CFD) as a configuration design tool. The configuration selected for the study involved complex flowfields for which substantial wind tunnel test data were available. The Euler code provided good estimates for the incremental effects of aileron deflections using both wing-alone and wing-fuselage modeling. In general, the addition of the fuselage to the wing-alone model improves estimates of the effects of leading edge and trailing edge flap deflections. Using a hybrid combination of Euler code results with incremental effects of the tails from a subsonic panel method provides good estimates of trimmed drag changes for small flap/aileron deflections.
1990-09-01
Technical Paper
901852
T. W. Purcell, C. J. Borland, E. N. Tinoco
Abstract A loosely coupled method for aeroelastic predictions of aircraft configurations is shown. This method couples an advanced structural analysis method with a CFD aerodynamics code in a modular fashion. This method can use almost any CFD code, so a validation of several such codes is shown to establish regions of validity for each code. Results from potential codes, an Euler code, and a Navier-Stokes code are shown in comparison with experiment. Viscous effects are included in most cases through a coupled boundary-layer solver or a turbulence model as appropriate.
1990-09-01
Technical Paper
901812
Ohyun Rho, Won Wook Kim, Chong Am Kim, Dong Ho Lee
The existing two-dimensional Euler code is extended to the three-dimensional flow problem in which the transonic flow around the double fin-body combinations was analysed. Ni's two-dimensional formulas are extended to the three-dimensional case and applied to the supersonic flow calculation over the double fin-body combinations. The numerical results have proved to be very accurate in predicting the pressure distribution and capturing the shock. The code extended to the three-dimensional flow analysis in the paper can be consequently used to estimate the aerodynamic characteristics of the complicated body.
1990-09-01
Technical Paper
901811
M. H. Lin, M. J. Sheu
A numerical method is developed to analyse the flow around an axisymmetric ogive-cylinder and an ellipsoid-cylinder bodies undergoing harmonic pitching motion in an uniform air free stream. The pressure distributions along the lengthwise and over the circumference of the body are calculated with fineness ratio of 3:1 at mean angle of incidence 0° and 5°. Results are presented for a range of frequency parameters and various mean angle of incidence in order to show the influence of the frequency parameter and the mean angle of incidence on the aerodynamic properties.
1990-09-01
Technical Paper
901810
Kevin W. Whitaker
A study was undertaken to improve the prediction of external (gas-to-blade) heat transfer coefficients in gas turbine engines. The study specifically investigated the effects of improved modeling of the eddy diffusivity of heat in the turbulence model. A two- dimensional boundary layer code, STAN5, was selected and modified by incorporating several different turbulent Prandtl number models. Results indicated that slight effects were attributable to the modified turbulence model. Boundary layer character (laminar, turbulent or transitioning) appeared to be much more significant.
1990-09-01
Technical Paper
901809
Clifford J. Obara, Paul M.H.W. Vijgen, Cynthia C. Lee, Michael S. Wusk
Correlation of in-flight boundary-layer transition experiments with linear boundary-layer stability theory contributes both to the validation of the numerical methods as well as the analysis of the measured transition process. Transition results obtained in a recent flight experiment, in which the extent of laminar flow and the transition process on the wing of a business-jet fitted with an instrumented glove section were determined, are analyzed. The experiment was conducted at freestream Mach numbers from 0.55 to 0.82, chord Reynolds numbers from 10 to 20x106, and leading-edge sweep angles of 17° to 20°. The growth of both Tollmien-Schlichting and crossflow instabilities are predicted using the en method for several flight conditions and the calculated “n-factors” at transition onset are correlated. Comparison of the measured dominant boundary-layer disturbance frequencies and the predicted unstable frequencies shows fair agreement for several of the flight conditions studied.
1990-09-01
Technical Paper
901808
Shen C. Lee, Chang R. Chen
Numerical solutions of the Reynolds-averaged Navier-Stokes equations were obtained with the two-equation K-ϵ turbulence model. Considering the low-Reynolds-number effect in the closed vicinity of a solid boundary, a stream function and vorticity method was developed to consider both the laminar and turbulent stresses throughout the two-dimensional, incompressible flowfield of any arbitrary geometry. At a low Reynolds number (Re = 30), the initially imposed disturbances around an airfoil are damped out; the flow is laminar. At a moderately high Reynolds number (Re = 1000), instability of laminar flow is obtained by exhibiting cyclic patterns in the stream function and vorticity distributions. Nevertheless, only laminar stress occurs in the entire flowfield. At a higher Reynolds number (Re = 106), turbulent stress, which is about three orders of magnitude larger than the laminar stress, occurs at a certain distance downstream of the leading edge and in the wake region.
1990-09-01
Technical Paper
901807
Michael J. Siclari, Paul Federico, Marc Mandel
A Computer Applications Laboratory (CAL) has been established at Grumman that is primarily concerned with the visualization of large sets of scientific data. The laboratory is a color graphics workstation environment and communications facility that allows scientists and engineers to quickly process and visualize large quantities of discrete data generated by an experiment or by a supercomputer numerical simulation. The graphical visualization capabilities are supported by in-house research into software development tailored to specific workstation hardware graphics. The CAL facility also serves as a site to the Numerical Aerodynamic Simulation (NAS) facility at NASA's Ames Research Center (ARC) allowing scientists, whose computer requirements involve massive physical memory, to access the CRAY-2.
1990-09-01
Technical Paper
901770
R. J. Meckstroth, R. Ahoor
: In the engineering design attempt to minimize customer complaints related to belt misalignment, a maximum belt pulley entry and pulley exit angle was chosen as a critical target for avoiding excessive belt wear and chirp noise. Calculating belt misalignment due to pulley misalignment from the perfect plane between two grooved pulleys is done using statistical stackup calculations in three dimensional space. This is usually done using available computer statistical simulation models and the most current component detail drawings. For backside pulleys (flat pulleys), such calculations can be performed only if the position of the belt as it contacts a backside pulley is known. Since the shape of the grooves no longer fixes the position of a belt at pulley entry point, the position of the belt at the backside pulley can not be determined by the position of the pulley groove.
1990-09-01
Technical Paper
901893
Kent Weber
Aerospace Planes are substantially different from both conventional aircraft and conventional rocket powered spacecraft and have a unique set of secondary power requirements. Although there are a wide variety of aerospace plane concepts incorporating both single and multiple stage to orbit, the various arrangements proposed have many common features. One of the primary common features unique to aerospace planes is the use of liquid hydrogen or liquid methane as the fuel. The cryogenic fuel storage temperature, while inconvenient from a fuel handling point of view, offers some synergistic cooling and power generation benefits unavailable to conventionally fueled aircraft. A second common, but unique, feature of aerospace planes is that the propulsion engines typically have no power extraction shafts, either because the propulsion engines are themselves shaftless (ramjets or scramjets), or because the core rotating parts are inaccessible (turboramjets, air turborockets).
1990-09-01
Technical Paper
901887
Karol Kerns
Research on operational use of data link technology as a means of exchanging information between aircraft and ground-based facilities has been underway for well over a decade. From this work, potentially useful data exist that remain largely unexploited for purposes of operational development. This paper reviews the simulation literature on data link communication between controllers and pilots to synthesize a base of useful, generalizable knowledge. General effects of the data link technology on the volume, speed, and timing of Air Traffic Control communications are analyzed for their operational significance. The analytic framework depicts data link effectiveness as interdependent with operational context, procedures and applications, and human interface design. Current research leaves many questions unanswered but consistently indicates that the combination of voice and data link communication outperforms either medium used by itself.
1990-09-01
Technical Paper
901888
Charles E. Knox, Charles H. Scanlon
Message exchange for air traffic control (ATC) purposes via data link offers the potential benefits of increasing the airspace system safety and efficiency. This is accomplished by reducing communication errors and relieving the overloaded ATC radio frequencies, which hamper efficient message exchanges during peak traffic periods in many busy terminal areas. However, the many uses and advantages of data link create additional questions concerning the interface among the human-users and the cockpit and ground systems. A flight test was conducted in the NASA Langley B-737 airplane to contrast flight operations using current voice communications with the use of data link for transmitting both strategic and tactical ATC clearances during a typical commercial airline flight from takeoff to landing. Commercial airplane pilots were used as test subjects.
1990-09-01
Technical Paper
901884
Michael C. Reynolds
Data link is the FAA's response to increases in air traffic communications. Data link can become a highly capable and quality tool for the National Airspace System (NAS) if a SYSTEMS CENTERED DESIGN APPROACH is taken. EVERY element must be carefully analyzed, designed and integrated as critical components of the NAS. Pilot performance in the NAS will be one of the keys to a quality system; tools must be provided that complement their experience, skills, and knowledge. The equipment must be ancillary to the pilots, not vice versa; equipment must be oriented towards solving problems without creating more or different kinds of problems.
1990-09-01
Technical Paper
901886
William H. Corwin, Hugo W. McCauley
Human factors issues related to the retrofit of data link in commercial transport aircraft are discussed. Topics that must be considered for data link implementation include, the loss of the “party line,” (i.e., the availability to all aircraft of information transmitted on a common voice frequency), and the “scheduling” of information to the flight crew. This paper focuses primarily on the human factors issues related to retrofit of Mode S. Retrofit is a difficult task because panel space accessible to flight crew members is limited. As with all cockpit equipment, data link implementation will have to comply with Federal Aviation Regulation 25.1523, which requires the manufacturer to address the conspicuity and ease of use of the data link device, and to assess the impact on crew workload.
1990-09-01
Technical Paper
901872
Jerry T. Dennis
The airline industry has yet to define a meaningful method for determining organizational fitness through internal analysis. Prior to deregulation, Airline Safety Departments and Programs were found in nearly every major and regional carrier. Today there are relatively few safety departments in comparison to pre deregulation. In addition, contemporary safety departments do not enjoy the same stature within the airlines; where department heads were formerly vice presidents, they are now directors or managers. Currently, the FAA is encouraging the industry to implement “Self Audit” programs based primarily on regulatory adherence. However, there is still no requirement or emphasis for a “Safety Department”. Additionally, there is no incentive for operators to establish a dynamic loss control or risk management program.
1990-09-01
Technical Paper
901873
Walter S. Coleman
The airlines, the Federal Aviation Administration and individual crewmembers have a shared responsibility, primarily through regulatory requirements, to ensure that the traveling public is provided with crewmembers who are fit to perform their duties.
1990-09-01
Technical Paper
901869
Robert J. Englar, David M. Schuster, Douglas A. Ford
Experimental investigations have been conducted to evaluate the aerodynamic performance and control of Unlimited-class hydroplanes racing at speeds exceeding 200 mph. These vehicles operate in very strong ground effect and may encounter unexpected disturbances such as wind gusts or waves, which can cause uncontrolled pitch-up and destruction. Specific test techniques have been developed in a modified subsonic wind tunnel to simulate these conditions, allow evaluation of the vehicle's aerodynamics and develop novel control surfaces. The paper presents details of these facilities and test techniques, associated wing-in-ground-effect tests, and characteristics of the pitching hydroplane as it transitions between in- and out-of-ground effect.
1990-09-01
Technical Paper
901870
R. Wade Allen, Anthony C. Stein, James C. Miller
Performance testing provides an important complement to urine testing as a determinant of fitness for duty. Performance testing can be conducted immediately to screen out impaired workers before they undertake safety related job functions. Urine testing involves the expense and delay of laboratory testing, and results relate more to life style than current on-the-job performance capability. This paper reviews performance based testing and discusses the development and application of two performance based screening devices. One device has the capability of rapidly screening for impaired psychomotor performance given previous baseline data. The second device provides the potential for screening psychomotor and divided attention performance without prior experience or baseline data.
1990-09-01
Technical Paper
901867
Louis T. Duncan
A comprehensive race car aero program contains three phases: initial body design, wind tunnel testing, and race track verification. This report compares wind tunnel test results and track data for the Churchill LeBaron race car which is sanctioned by the Automobile Racing Club of America (ARCA). During the wind tunnel phase of testing, several runs were conducted specifically to be repeated during track testing at the Talladega* and Atlanta* tracks. At both tracks the race team first conducted their usual engine and chassis set up runs, then dedicated a series of runs to aero testing. At Talladega, incrementally reducing drag on five consecutive runs produced a lower lap time on each run. At the Atlanta track, reducing lift on six runs produced corresponding reductions in lap time. This report presents the results.
1990-09-01
Technical Paper
901712
Yoshishige Ohyama, Minoru Ohsuga, Hiroshi Kuroiwa
Abstract Mixture formation and the ignition process in 4 cycle 4 cylinder spark ignition engines were investigated, using an optical combustion sensor that combines fiber optics with a conventional spark plug. The sensor consists of a 1-mm diameter quartz glass optical fiber cable inserted through the center of a spark plug. The tip of the fiber is machined into a convex shape to provide a 120-degree view of the combustion chamber interior. Light emitted by the spark discharge between spark electrodes and the combustion flames in the cylinder is transmitted by the optical cable to an opto-electric transducer. As a result, the ignition and combustion process which depends on the mixture formation can be easily monitored without installing transparent pistons and cylinders. This sensor can give more accurate information on mixture formation in the cylinders.
1990-09-01
Technical Paper
901710
Tohru Hamamoto, Seiji Omura, Norikatsu Ishikawa, Toshiki Sugiyama
A new engine cooling fan system has been developed, in which the fan is driven by a hydraulic pump and motor and controlled electronically by a computer. By utilizing the hydrostatic power under precise control, the fan generates not only high airflow volume but also optimum flow rate for the various engine conditions. Also in this system, a relatively high efficiency is gained because the clearance between the tip of the fan blade and a shroud designed to be short, thanks to the installation of the fan on the radiator. As the result of these functions, the following features have been obtained which are superior to conventional fan systems like a engine-driven fan with fluid coupling or an electric-motor fan. (1) Reduced fan noise (2) Improved fuel economy (3) Small size and light weight
1990-09-01
Technical Paper
901714
Akihiko Sobue, Tamio Kawamura, Toshihiro Ninomiya
Abstract The SR engine is a new medium-size, all aluminum (cylinder block, head, rocker cover and oil pan) in-line 4-cylinder gasoline powerplant developed as a replacement for CA engine in Nissan's compact passenger cars. The development aim set for this engine was to achieve excellent power output and ample torque in the middle-and high-speed ranges, as well as a clear, linear engine sound up to the red zone. These performance targets have been achieved through the use of the 4-valve-per-cylinder DOHC design featuring a Y-shaped valve rocker arm system. This system allows a straight intake port for high power output and a narrow valve angle for a compact combustion chamber. The result is ample torque output as well as good fuel economy.
1990-09-01
Technical Paper
901713
Diana D. Brehob, Duane R. Amlee
The common method for achieving less than full power operation in a spark ignition (SI) engine is reducing charge density via a throttle. However, a significant fuel economy penalty is associated with the pumping losses across the throttle valve. An alternative method to aid in reducing fresh charge density has been investigated on an Oldsmobile Quad-4 engine: exhaust gas recirculation in combination with inlet air heating. Brake thermal efficiency gains of about 6% were realized. The exhaust hydrocarbon increases associated with EGR were mitigated largely by inlet air heating.
1990-09-01
Technical Paper
901707
Susumu Masutomi, Kiyotaka Ise, Kimio Tamura
A new ABS and Traction control system (TRAC system) has been developed and put into mass production in a new model LEXUS LS400. The TRAC system controls Sub-Throttle Valve and brake hydraulic pressure independently for left and right wheels. To realize the ABS and TRAC system,it is necessary for the Electronic Control Unit (ECU) to process complex algorithm and high speed calculation. The ABS and TRAC ECU for LEXUS LS400 is constructed by 3 TOYOTA custom 8-bit single chip microcomputers. Each CPU performs wheel speed calculation,ABS control and TRAC control,sharing the common data through high speed serial communication. This paper describes the function of each CPU,the method of CPU communication and fail safe function in the ECU.
1990-09-01
Technical Paper
901706
Yasuo Ishiguro, Yoshito Katoh, Chisao Hayashi, Mistuo Koide, Masaru Nakano, Hirohito Minoshima
In today's manufacturing environment, it has become necessary to develop intelligent robots which are adaptable to changing process requirements. To attain this goal, a key robot technology involving new real time control algorithms has been developed. The algorithms govern the 3D position and orientation of the robot. Initially, a simulation method was used to study the achievable system accuracy. From the results of computer simulations, it was determined that the algorithms can achieve a high tracking accuracy of ± 0.5 mm at a velocity of 300 mm/sec (4 times higher than conventional sensory control speeds). For a sensory feedback system, delays in tracking movements are inherent. This is due to the calculation time required for control and to the servo response. To solve this problem, a sensor is positioned at a predetermined distance in advance of the tool in the direction of travel.
1990-09-01
Technical Paper
901709
Walt Sousa
1990-09-01
Technical Paper
901727
Michael Grohn
The valve timing of internal-combustion engines usually represents a compromise with regard to the requirements placed on power output and torque. Extensive operation process simulation and measurements on real engines have shown that it is quite possible to achieve considerable improvements with constant valve lift and differing intake timing. Varying valve lift with engine speed is not necessary, since in this way only minor torque improvements can be gained. The requirements are met sufficiently with two timing settings. Extensive system analyses and concept studies led to the mechanically/hydraulically actuated camshaft adjuster which is described below in detail, and which is used in the new four-valve Mercedes-Benz engines. The camshaft adjuster is controlled in accordance with the requirements of engine and vehicle by the gasoline injection control unit, depending on engine speed and load.
1990-09-01
Technical Paper
901726
Dojoong Kim, Joseph W. David
A numerical modeling technique is proposed for computer simulations of high speed valve train dynamics. The dynamic terms in the valve spring reaction forces are calculated using linear vibration theory for given kinematic valve motions. Because the spring dynamics are analyzed before the time stepping integration, spring surge phenomena can be included without using additional computer time. Consequently, valve train dynamics can be simulated very quickly without noticeable errors in accuracy. The experimental results prove the computer model developed here is accurate and also computationally efficient.