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Technical Paper

Transient and Steady State Performance Characteristics of a Two-Wheel-Steer and Four-Wheel-Steer Vehicle Model

1991-09-01
911926
Using a three-degree-of-freedom vehicle model (side-slip, yaw and roll degrees of freedom) and a nonlinear, saturating rire model, the behavior of a typical exemplar vehicle (1986 Dodge Lancer Turbo) was simulated. Steady state performance was examined through simulating a skidpad lateral accelerarion maneuver. A lane change maneuver was used to reprcsenr transient performance characteristics. A few simple experiments were conducted wirh rhe exemplar vehicle to establish parameters and verify some performance properties. Results of both steady srare and rransienr simulations showed that four -wheel steer offers lirrle or no demonstrated performance advanrages over two-wheel steer.
Technical Paper

The Effects of Suspension Stiffness on Handling Responses

1991-09-01
911928
Abstract The purpose of this paper is to investigate the influence of suspension roll stiffness on handling responses. A linear mathematical model is utilized to scrutinize responses on sideslip, yaw velocity and roll angle. Due to different sensitivity to suspension roll stiffness, the influence on an oversteer and an understeer vehicle is very distinct. An oversteer vehicle possesses high sensitivity to suspension stiffness at high speeds. Forward speed also plays an important role. Responses in root locus plots and steady state gains are illustrated in this study.
Technical Paper

Multipurpose Models of Vehicle Dynamics for Controller Design

1991-09-01
911927
As an aid in conceptual development of sophisticated integrated control strategies for torque, brakes, steering, and suspensions in ground vehicles, reasonable physical system models are necessary. These models must be sufficiently complete to include the important dynamics, but not so complex that insight is obscured. This paper develops several vehicle models of varying complexity that can aid in the design synthesis of controllers. The potential uses of these models is described.
Technical Paper

Possible Compressor Problems in Handling HFC-134a Car Air Conditioning Systems

1991-09-01
911929
Several field problems are anticipated with HFC-134a systems. To be evaluated and clarified are the impacts upon: compressors and systems of chlorine based solvents left in the system from flushing or parts cleaning; mixing in CFC-12; mixing the new lubricants with mineral oil; the effects of certain lubricants and HFC-134a's high hygroscopicity and others. The whole industry should share information and endeavor to maintain the reliability of the new systems from a service engineering standpoint. STARTING IN 1991 the ozone safe HFC-134a refrigerant is expected to replace the conventional CFC-12 in car air conditioning systems and in model years 1994-1995 the major portion of the market will be the new systems. The components/elements and parts used in the new air conditioning systems will embody different designs with new materials which are now considered to be compatible with the new refrigerant-lubricant mixtures.
Technical Paper

The Development of a Calculation Model to Estimate the Heat Flow by Heat Transfer and Sun Radiation into Passenger Cars

1991-09-01
911932
A calculation model has been developed to accurately estimate the heat transmission through the wall of the passenger compartment of a car. This calculation model estimate the specific heat flow by heat transfer into passenger cars using the calculated outside surface temperatures of the passenger compartment. If the real outside surface temperatures are known, the specific heat flow into the passenger compartment can be calculated precisely without compromising the physical properties of air near the outside surface of the compartment wall. The cooling load can be determined using the calculated outside surface temperature of a vehicle, in the earliest stage of a new car design.
Technical Paper

Engine Compartment Air Management for Engine Cooling and Air Conditioning System Performance

1991-09-01
911933
: Engine Cooling and Air Conditioning tests were performed using a sports utility vehicle with a V-6 engine. The original vehicle was equipped with an engine driven fan. This vehicle was modified by adding electric motor driven fans, air path sealing and advanced heat exchangers in a predetermined test configuration. Engine cooling performance and air conditioning performance were evaluated at each step. Identical grade load and idle tests were conducted with this vehicle at each step. The V-6 sports utility vehicle was selected due to its use of an engine driven fan. The grade load of 8.7% was selected due to off road use by the consumers. The results of the testing showed that engine cooling performance and air conditioning performance were improved by using electric motor driven fans, air path sealing and advanced heat exchangers.
Technical Paper

A Calculation of Penetration of the Jet Issuing Normally into a Cross Flow Across a Wall Boundary Layer

1991-09-01
912029
An Increase in jet penetration due to the wall boundary layer is determined in the flow field including an aerodynamic interference between the wall boundary layer and the jet. The aerodynamic effect of the wall boundary layer is replaced by that of a secondary vortex filament resulting from vorticity in the wall boundary layer. A differential equation governing the increase in jet penetration is derived using the circulation around the secondary vortex filaments, its induced velocity and the empirical decay law of the jet axial velocity along the jet centerline. The circulation around the secondary vortex filament is estimated according to Hawthorne's theory (1)* and expressed in terms of aerodynamic characteristics of the wall boundary layer. A numerical example of the present analysis shows a fairly good agreement with the experiment. This indicates that the used vortex flow model simulates the real flow conditions well.
Technical Paper

Improving Automatic Transmission Shift Quality by Feedback Control with a Turbine Speed Sensor

1991-09-01
911938
Shift quality in automatic transmissions is greatly affected by deterioration and variation of engine torque, hydraulic pressure control valves, friction elements and other factors. This paper presents a new control system that improves shift quality by using a turbine speed sensor to monitor the shift duration, particularly the duration of the inertia phase. The use of feedback control to vary the line pressure according to the shift duration makes it possible to eliminate the effects of aging and component variability. Other factors affecting shift quality, such as atmospheric pressure, road gradient and additional engine load from the air conditioner and alternator, were also examined, and it was found that their effects can be virtually eliminated through feedback control. The inertia phase usually becomes shorter as the engaging clutch capacity increases. However, an extremely small torque capacity can cause a short inertia phase, resulting in a large torque disturbance.
Technical Paper

Static Characteristics of a Two-Phase Fluid Loop System

1991-09-01
912023
The Two-Phase Fluid Loop (TPFL) System is a heat transport system for future large spacecraft, using latent heat of coolant. TOSHIBA Co. has developed a ground test facility capable of dissipating a 5kw heat load and tested the components of that facility since 1988. As a next phase, static characteristics of the TPFL system are being studied. In this paper, static behaviors under heat load variation are presented as results of the experimental study and the numerical simulation. For the experimental study, the above-mentioned ground test facility was used. In this facility, heat is finally dissipated to the heat exchanger using brine as a heat sink. In order to determine static behaviors for an actual radiator heat rejection system used in orbit, numerical simulation was carried out. To confirm the analytical model used in the numerical simulation, the numerical result and the experimental result were compared.
Technical Paper

Aero-Structural Integrated Design of Forward Swept Wing

1991-09-01
912021
Forward swept wing (FSW) is known to have excellent performance relative to aft swept wing. The practical application, however, has been limited due to its structural divergence characteristics. The current progress in materials, especially anisotropic composites has opened up new future for FSW. This paper describes design study of FSW for transonic transport looking for high drag divergence performance. Inverse code is applied to FSW aerodynamic design to achieve isobar design concept. The performance is verified by transonic wind tunnel test. The paper also mentions the development of aero-structural integrated design tool, a combination of aerodynamic analysis code and structural analysis code, which is essential to FSW wing development.
Technical Paper

Aerodynamic Characteristics Near the Tip of a Finite Wing by a Panel Method

1991-09-01
912020
The aerodynamic characteristics around a wing tip are investigated with a first order panel method. The geometry chosen for the study is a rectangular wing of aspect ratio 8.43,with RAF6 airfoil of 10% thickness ratio. The panel method gives similar aerodynamic characteristics to experimental ones even near the tip, such as a dominant suction pressure distribution present near the trailing edge around the tip, and the increase in the local lift and drag at the very narrow region of the tip. These properties are caused by the strong spanwise velocity component around the wing tip, the inviscid effects of which are described in detail, with respect to pressure coefficient, local lift and drag coefficients, downwash, and vorticity on the wing.
Technical Paper

A Simplified-Model Approach to Group Combustion of Fuel Spray

1991-09-01
912032
Combustion of a liquid fuel spray distributed in a uniform stream was analyzed with a distributed source model. In this model, each fuel droplet of the spray is expressed mathematically by the moving source, of which the strength is to be determined by the relevant governing equations and boundary conditions. The main equation is an integral equation which expresses the inter- relation among strengths of fuel droplets in the spray. Given the assumptions of a uniform velocity of the stream and zero-relative velocity of fuel droplets, the spatial variation of the droplet radii can be expressed by a differential equation with respect to a spatial coordinate y. Thus, the set of coupled equations can be solved numerically and iteratively. Then nature of the distributed spray combustion in the convective flow is seen to be governed by two non-dimensional parameters, known to be group combustion numbers.
Technical Paper

Multidimensional Euler/Navier-Stokes Analysis for Hypersonic Equilibrium Gas

1991-09-01
912026
Numerical simulations of hypersonic flow around a 2-D cylinder and a 3-D complete reentry vehicle have been carried out by solving Euler/Navier-Stokes equations which incorporate the equation of state for an equilibrium gas. The governing equations are solved by an implicit finite volume TVD (Total Variation Diminishing) upwind scheme using a two-equation turbulence model for a viscous flow. Curve-fits for the thermodynamic and transport properties of an equilibrium air are adopted in order to estimate real gas effects. Convective fluxes are calculated by the Roe's approximate Riemann solver generalized for an equilibrium gas. The results of hypersonic flow analysis using this code suggest us that the real gas effects, such as chemical reaction, are not negligible to predict the hypersonic flow characterisics acculately.
Technical Paper

Demonstration of Gas Liquid Separation Under the Microgravity by Aircraft KC-135

1991-09-01
912024
Liquid reservation and liquid-gas separation system is an important factor in a thermal control system and an environmental control system of spacecraft. A surface tension tank is one of the important device in the system. A functional model and partial models were fabricated and their behavior verification tests were conducted under the microgravity. The experiment was conducted in NASA KC-135 reduced gravity plane in 1991 January. Expelling function was verified with a functional model. The tank has channels with fine mesh screen and expels liquid only. The expelled distilled water is returned into the tank again, the ratio of liquid to gas is kept constant, and the flow rate of the discharged water is a parameter. The liquid behavior was recorded on video tape and acceleration data was recorded on a data recorder.
Technical Paper

An Economic Approach to Accurate Wing Design

1991-09-01
912008
Abstract An interactive boundary-layer method is described for computing three-dimensional transonic flows on wing/body configurations. The method combines Euler solutions with viscous flow solutions obtained from an inverse boundary-layer method with an interaction law based on the extension of the Hilbert integral formulation used for two-dimensional flows. Depending on the complexity of the flowfield, two versions of Keller's box scheme are used, the regular box scheme in regions of positive crossflow and no separation, and the characteristic box scheme in regions of negative crossflow and flow separation. Preliminary calculations performed for a modern transport wing show good agreement with experimental data and indicate that wing/body configurations in transonic flows can be analyzed with good accuracy with this method at substantial savings of computer time.
Technical Paper

Experimental and Numerical Studies of Radiation Emission from High-Temperature Air Behind 10 km/s Shock Waves

1991-09-01
912025
In order to estimate the exact heat transfer from shock-heated air to the re-entering space vehicles, one needs the accurate understanding of its radiative characteristics. The 10 km/s shock waves are produced by a free-piston, double-diaphragm shock tube, and the total and spectral-resolved radiation intensities of the shocked air are observed by using an image converter camera and a pair of photomultipliers. The numerical analysis is carried out for one-dimensional, steady hypersonic flows with non-equilibrium chemical reactions of hot air, including the evaluation of radiation intensity. The double-peak characteristic of radiation intensity for the shock waves above 10 km/s and the time-lag of radiation peak for different wave length are experimentally observed and qualitatively reproduced in numerical simulation.
Technical Paper

Results and Lessons Learned from the STOL & Maneuver Demonstration Program

1991-09-01
912005
The STOL and Maneuver Technology Demonstrator (S/MTD) Program has validated a set of technologies that give a supersonic fighter all-weather Short Takeoff and Landing (STOL) performance while also enhancing up-and-away maneuverability. Significant reductions in both takeoff and landing distances, compared with the unmodified F-15, have been measured. The additional pitch control power of thrust vectoring has been demonstrated up to 30° angle of attack. The effectiveness of up-and-away reversing has been identified. First, major flight test results are presented and then lessons learned from this integration program are discussed.
Technical Paper

Update of the X-29 High-Angle-of-Attack Program

1991-09-01
912006
The X-29A forward-swept wing flight research aircraft flight envelope was expanded to 66°-angle of attack in 1990. This work was accomplished at the NASA Dryden Flight Research Facility in Edwards, California, using Grumman aircraft and United States Air Force personnel assistance. The flight envelope expansion was accomplished through a carefully planned buildup approach using the number 2 X-29 aircraft and a well documented high-angle-of-attack database established from wind-tunnel results, radio controlled subscale drop model results, and from previous X-29 aircraft number 1 flight data below 22.5°-angle of attack. Following the flight envelope expansion, a military utility evaluation was conducted to investigate the tactical utility of the X-29 configurations at high-angle-of-attack, slow-speed flight conditions.
Technical Paper

Numerical Simulation of a Supersonic Jet Impingement on a Ground

1991-09-01
912014
Abstract An impingement of axisymmetric supersonic jet on the ground is simulated numerically to evaluate the jet flow configuration on the ground, which inclines from 0 to 45 degrees, with a real gas assumption for two-dimensional simulations and with an ideal gas assumption for three-dimensional simulations. A solid particle-suspended two-phase jet impinging on the ground is also solved using the Euler equations for the solid particle-phase with a real gas assumption. An explicit TVD-Upwind scheme is used for the gas-phase and an explicit Flux Vector Splitting Upwind scheme for the solid-phase. Numerical results of a vertically impinging jet to the ground show that a plate shock forms just above the ground for the cases of the single-phase and two-phase jet. Then the jet flow is curved along the ground after hitting the ground to form the so-called wall jet, which is expanded and recompressed alternately along the ground.
Technical Paper

Recent Applications of the FNS Zonal Method to Complex Flow Problems

1991-09-01
912003
Newly developed zonal method using the interface scheme based on the Fortified Navier-Stokes concept is applied to steady and unsteady flow problems. Two computational results are shown as application examples to unsteady flow problems. One problem is a train moving into a tunnel and the other problem is a blast wave propagation. These problem require the accuracy enhancement and the problem adaptability, both of which are important obstacles of the current CFD technology. The computed result indicates that the present method alleviates the difficulty with simple modification of the existing codes. Steady flow problems include supersonic intake flow simulation and three dimensional simulation of the complex body configuration. The results indicate that the present method alleviate the difficulty of the simulation of complex flow configuration.
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