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Results are presented from a study on the use of Computational Fluid Dynamics (CFD) for automotive underbody design. A diffuser-equipped bluff body with endplates was examined in ground effect at varying ride heights in configurations with and without wheels. The study was performed using commercial CFD, Fluent© 6.3.26. CFD data is compared to experimental work done with similar bodies by Cooper et al. [1, 2], George et al. [3, 4], Zhang et al. [5, 6], and others [7, 8, 9]. Emphasis is made on the study of vortex structures in bluff body flow. Various mesh geometries and solvers were explored with computational models designed to operate on single-processor workstations or small networks. Steady-state solutions were modeled for all cases; boundary layers were approximated with wall functions. CFD results for lift coefficient measured within 15-25% of experimental cases, dependent on solver. Qualitative results matched well with experimentally measured flow structures.

The crew diet in a bioregenerative lifesupport system will be a combination of foods grown and processed in’situ with resupplied prepackaged foods and ingredients. The ideal diet should be palatable, nutritionally adequate, varied and low in cost. This diet can be obtained by adopting an optimization strategy combining panel acceptance data, nutritional analyses and mission specific ESM (equivalent system mass) cost estimates for a large selection of foods and ingredients. A linear programming routine selects the lowest cost diet from the foods surveyed, subject to constraints on nutrient content, food acceptability, and variety. The rigor of these constraints is a key factor in determining the cost of the diet (s) they define. By varying individual constraints over several optimizations, we can estimate sensitivity of overall costs to a particular nutrient, or even an intangible quality such as acceptability, while controlling other aspects of the diet.

This paper is taken from work completed by the first author as a member of the 1999 Cornell University Formula SAE Team and discusses several of the concepts and methods of frame design, with an emphasis on their applicability to FSAE cars. The paper introduces several of the key concepts of frame design both analytical and experimental. The different loading conditions and requirements of the vehicle frame are first discussed focusing on road inputs and load paths within the structure. Next a simple spring model is developed to determine targets for frame and overall chassis stiffness. This model examines the frame and overall chassis torsional stiffness relative to the suspension spring and anti-roll bar rates. A finite element model is next developed to enable the analysis of different frame concepts. Some modeling guidelines are presented for both frames in isolation as well as the assembled vehicle including suspension.

The validity and usefulness of low-complexity “fast-turnaround CFD” for motorsports design is investigated using results from three different combined experimental and CFD analyses of racing or high-speed vehicles. Analyses using both wind tunnel experiments and CFD simulations (with commercial software and moderate computing resources) found good agreement in some aspects of interest over a variety of applied situations. Key results were the ability for relatively simple CFD models to consistently predict CL in complex flows within 15-25% of experimental findings, predict the effect of design changes on flow, and accurately show qualitative flow phenomenon. However, CD values were not accurately predicted with the low-complexity simulations. Simulations were run using the commercial Fluent© 6.3 application. Experimental results were performed in the Cornell University 4 by 4 foot wind-tunnel.

The Society of Automotive Engineers Fatigue Design & Evaluation Committee [SAE FD&E] is actively working on a total life project for weldments, in which the welding residual stress is a key contributor to an accurate assessment of fatigue life. Physics-based welding process simulation and various types of residual stress measurements were pursued to provide a representation of the residual stress field at the failure location in the fatigue samples. A well-controlled and documented robotic welding process was used for all sample fabrications to provide accurate inputs for the welding simulations. One destructive (contour method) residual stress measurement and several non-destructive residual stress measurements-surface X-ray diffraction (XRD), energy dispersive X-ray diffraction (EDXRD), and neutron diffraction (ND)-were performed on the same or similarly welded samples.

A prototype packed bed convective dryer has been studied for use in an energy-efficient closed air-loop heat-pump drying system for astronaut cabin waste. This paper presents a transient continuum model for the heat and mass transfer between the air and wet ersatz trash in the cylindrical drying vessel. The model is based on conservation equations for energy and moisture applied to the air and solid phases and its formulation includes the unique waste characteristic of having both dry and wet solids. It incorporates heat and mass transfer coefficients for the system measured on an ersatz trash in the dryer vessel, and experimentally determined moisture sorption equilibrium relationship for the wet material. The resulting system of differential equations is solved by the finite-volume method as implemented by the commercial software COMSOL. The validated model will be used in the optimization of the entire closed-loop system consisting of dryer, condenser, and heat-recovery modules.

A low-pressure direct injection fuel system for spark ignition direct injection engines has been developed, in which a high-turbulence nozzle technology was employed to achieve fine fuel droplet size at a low injection pressure around 2 MPa. It is particularly important to study spray characteristics in the near-nozzle region due to the immediate liquid breakup at the nozzle exit. By using an ultrafast x-ray area detector and intense synchrotron x-ray beams, the interior structure and dynamics of the direct injection gasoline sprays from a multi-orifice turbulence-assisted nozzle were elucidated for the first time in a highly quantitative manner with μs-temporal resolution. Revealed by a newly developed, ultrafast computed x-microtomography technique, many detailed features associated with the transient liquid flows are readily observable in the reconstructed spray.

A computer model of a tractor-semitrailer is developed which extends that given by Mikulcik in SAE 710045 (Ref. 10 of paper). The extended model allows translation, yaw, roll, and pitch of both tractor and semitrailer. Lateral and fore-and-aft weight transfer is displayed. Wheel dynamics are included, and effects of wheel slip, slip angle, vehicle speed, and tire load are used in the calculation of the tire forces. The vehicle is maneuvered by a simulated driver who specifies the front-wheel steer angle and the brake torques. The ability of the model to accurately describe a real vehicle is studied by using the model to simulate a full-scale experimental test. The model is also used to study two types of proportional braking for a tractor-semitrailer executing a large-radius turn on a wet asphalt track.

This paper describes the addition of tandem-drive axles and tractor suspension dynamics to a digital computer model of a tractor-semitrailer truck. The extended model provides 22 degrees of freedom for the vehicle. Two degrees of freedom are included for the motion of each tractor axle; vertical tire flexibility, tandem-axle suspension jacking, and tandem-axle roll steer are also included in the extended model. The features of the previous vehicle model (based on the work of Mikulcik) are retained in the extended model. These features include nonlinear equations for translation, yaw, pitch, and roll of both the tractor and the semitrailer (except as these motions are constrained by the fifth wheel), wheel rotation dynamics, and antiskid brake control. The model also includes a simulated “driver” which specifies the steering angle and the air pressure applied to the brakes.