James T. Heineck

Progress in Reducing Aerodynamic Drag for Higher Efficiency of Heavy Duty Trucks (Class 7-8)

This paper describes research and development for reducing the aerodynamic drag of heavy vehicles by demonstrating new approaches for the numerical simulation and analysis of aerodynamic flow. In addition, greater use of newly developed computational tools holds promise for reducing the number of prototype tests, for cutting manufacturing costs, and for reducing overall time to market. Experimental verification and validation of new computational fluid dynamics methods are also an important part of this approach. Experiments on a model of an integrated tractor-trailer are underway at NASA Ames Research Center and the University of Southern California. Companion computer simulations are being performed by Sandia National Laboratories, Lawrence Livermore National Laboratory, and California Institute of Technology using state-of-the-art techniques, with the intention of implementing more complex methods in the future.

DOE's Effort to Reduce Truck Aerodynamic Drag Through Joint Experiments and Computations

Class 8 tractor-trailers are responsible for 11-12% of the total US consumption of petroleum. Overcoming aero drag represents 65% of energy expenditure at highway speeds. Most of the drag results from pressure differences and reducing highway speeds is very effective. The goal is to reduce aerodynamic drag by 25% which would translate to 12% improved fuel economy or 4,200 million gal/year. Objectives are: (1) In support of DOEs mission, provide guidance to industry in the reduction of aerodynamic drag; (2) To shorten and improve design process, establish a database of experimental, computational, and conceptual design information; (3) Demonstrate new drag-reduction techniques; and (4) Get devices on the road. Some accomplishments are: (1) Concepts developed/tested that exceeded 25% drag reduction goal; (2) Insight and guidelines for drag reduction provided to industry through computations and experiments; (3) Joined with industry in getting devices on the road and providing design concepts through virtual modeling and testing; and (4) International recognition achieved through open documentation and database.

Planar Velocimetry of Jet/Fin Interaction on a Full-Scale Flight Vehicle Configuration

Stereoscopic particle image velocimetry has been implemented in a production-scale transonic wind tunnel for studying jet/fin interaction created by exhaust plumes from spin rockets on a full-scale model of a finned body of revolution. Data acquired just upstream of the leading edge of the fin root clearly display the counter-rotating vortex pair that dominates the interaction far field and the remnant of the horseshoe vortex near the vehicle surface. The counter-rotating vortex pair is distinctly asymmetric due to originating from a scarfed nozzle and displays some rotation with respect to the model surface. Velocity fields measured over a range of flowfield conditions and model orientations show that the vortex of negative sign is always closer to the fins than its positive counterpart and does not greatly change location as flowfield parameters are altered. The circulation of this vortex correlates with a reduction in the simultaneously measured vehicle roll torque. Further correlations are hindered by untreatable bias errors in the velocimetry. Instead, a model of the vortex structure derived from the velocimetry data reveals that the angle of attack induced upon the fins by the counter-rotating vortex pair correlates with the roll torque loss. Similar correlations suggest that in level flight this effect is dominant, but at angle of attack the horseshoe vortex on the windward side has an additional influence.

Results from the Mars Science Laboratory Parachute Decelerator System Supersonic Qualification Program

In 2010 the Mars Science Laboratory (MSL) Mission will deliver the most massive and scientifically capable rover to the surface of Mars. To deliver this payload, an aerodynamic decelerator is required to decelerate the entry vehicle from supersonic to subsonic speeds, in advance of propulsive descent and touchdown on Mars. The aerodynamic deceleration will be accomplished by a mortar-deployed 21.5-m Viking-type disk-gap-band parachute (DGB), and will be the largest extra-terrestrial decelerator in the history of space exploration [1]. The parachute will deploy at up to Mach 2.2 and 750 Pa, resulting in the highest load and speed experienced by a parachute on Mars. The MSL parachute extends the envelope of the existing heritage deployment space in terms of load, size and Mach number. This has created the challenge of leveraging the existing heritage supersonic- high-altitude database, implementing a ground-based qualification program, and quantifying known aerodynamic instabilities associated with supersonic operation in the Mach regime of the MSL deployment. To address these challenges MSL has embarked upon a physics-based modeling and validation program to explore the fundamental physics associated with DGB-parachute operation in supersonic flow. The functional dependence of parachute performance and stability on Mach number, Reynolds number, parachute size, entry-vehicle size and parachute to entry vehicle proximity, is under investigation. The quantitative understanding garnered from this analytical effort will be used to leverage the existing heritage database of the Viking Lander, Viking Balloon Launched Decelerator Test (BLDT), Mars Pathfinder (MPF) and Mars Exploration Rover (MER) programs for the larger scale, deployment conditions, and modern construction techniques of the MSL parachute system. The physics-based modeling and validation effort includes the development of a coupled fluid and structural solver, i.e. fluid-structure-interaction code, and supersonic wind-tunnel experiments with subscale representations of the flight configuration.

Aerodynamic Drag of Heavy Vehicles (Class 7-8): Simulation and Benchmarking

This paper describes research and development for reducing the aerodynamic drag of heavy vehicles by demonstrating new approaches for the numerical simulation and analysis of aerodynamic flow. Experimental validation of new computational fluid dynamics methods are also an important part of this approach. Experiments on a model of an integrated tractor-trailer are underway at NASA Ames Research Center and the University of Southern California (USC). Companion computer simulations are being performed by Sandia National Laboratories (SNL), Lawrence Livermore National Laboratory (LLNL), and California Institute of Technology (Caltech) using state-of-the-art techniques.

Application of Three-component PIV to the Measurement of Hypervelocity Impact Ejecta

Three-component Particle Image Velocimetry has been applied to the measurement of hypervelocity ejecta from meteoritic impact experiments. This work represents the first attempt at measuring ejecta from a ballistic event using the PIV technique. The ejecta particles are measured directly, within a plane, at any controlled instant after the impact. The particle trajectories are observed at all azimuthal positions relative to the impact point thus revealing both the shape of the curtain and the distribution of velocities at a given instance. By seeding the target with 10 mm hollow spheres, the fluid flow associated with the impact in an atmosphere is simultaneously observed with the ejecta. 3C PIV is demonstrated to be an ideally suited technique for investigations on ejecta trajectories, ejecta curtain morphology and the fluid mechanics in the presence of an atmosphere. Sample results are presented.

Photogrammetric recession measurements of ablative materials in arcjets

This paper describes an optical method for measuring the recession time histories of ablative thermal protection system (TPS) materials as they are tested in an arcjet facility. The method is non-intrusive and requires no external light source or modifications to the test article. It does require, first, a test article that exhibits texture as it ablates, and, second, high-resolution video images of the ablating surface from at least two directions. Software automatically reads the sequences of images and, by successive image cross correlation, tracks the deformation of a surface grid that conforms to the shape of the test article. Standard photogrammetric transformations are used to convert image-plane displacements of the surface grid to object-space displacements. The method yields a time history of the displacement of each node of the grid for the full time that the test article is exposed to the arcjet flow. Measurements have been made during many tests in the 60 MW arcjet at NASA Ames Research Center, including tests of TPS materials for the Orion Crew Exploration Vehicle and Mars Science Laboratory. The photogrammetric recession measurements have been in good agreement with post-test measurements of the change in thickness of the test articles.

Predicting Camera Views for Image-Based Measurements in Wind Tunnels

This paper describes a method for creating virtual images of wind-tunnel scenes and shows how these images can be used to plan image-based measurements. The method has been implemented as a stand-alone Windows application and was used extensively to plan Particle Image Velocimetry (PIV) measurements for recent wind-tunnel tests of a 3% scale model of the Space Shuttle. Real and virtual images from these tests are presented to demonstrate the methodology.

Background-Oriented Schlieren Imaging for Full-Scale and In-Flight Testing

Background-oriented schlieren (BOS) methods suited for large-scale and in-flight testing are presented with special emphasis on the detection and tracing of blade tip vortices in situ. Retroreflective recording and photogrammetric epipolar analysis for the computation of the vortices’ spatial coordinates in the wind tunnel are described. Feasibility and fidelity of referencefree BOS in conjunction with natural formation backgrounds and related evaluation methods are discussed, additionally, illustrating their simplicity and robustness. Results of successful image acquisition from a chaser aircraft are presented allowing vortex wakes to be identified at a wide range of flight attitudes, including complex maneuvers.

Mirror-Based Image Derotation for Aerodynamic Rotor Measurements

The current level of technology allows image based temperature, pressure and skin friction measurements at exposure times in the order of milliseconds. Though CCD and CMOS sensors of increasing sensitivity are continuously under development and being brought into the market, it will take some time before the majority of recording techniques allows for exposure times short enough to avoid motion blur during rotating blade recording. It has been demonstrated that image de-rotation can be achieved with a rotating mirror system. Such a system, which is able to provide very high-speed and easily adjustable image de-rotation, has been described in this article. Problems such as the angular control of the rotating mirror and its synchronization with the camera have been solved successfully. A theoretical model detailed enough to choose appropriate recording parameters for the application of a rotating mirror system has been presented.