Bruce Storms

Aeroacoustic measurements of slat noise on a three-dimensional high-lift system

Experimental results are presented for the aerodynamics and acoustics of an unswept wing with a half-span flap and a full-span slat. Concurrent aerodynamic and acoustic measurements were obtained for high-lift riggings representative of landing-approach configurations. Phased microphone array measurements indicate that slat gap noise is most significant for high slat deflections where the slat is lightly loaded. More specifically, the peak noise level for the 25deg slat deflection was 20 dB higher than that of the 9-deg slat deflection. Measurements of intermediate angles indicate a gradual decrease in slat noise as slat deflection is decreased. Strouhal frequency scaling of the 25deg slat configuration suggests that vortex shedding from the slat trailing edge may be an important noise mechanism. However, a non-linear relationship between slat noise level and angle of attack suggests a more complex phenomenon. Computational results detail the strength of the shear layers in the slatcove flow field. Variations in the slat-cove shear layers with slat deflection and angle of attack are presented. From correlations between the computed results and the measured acoustics, it is hypothesized that a KelvinHelmholtz instability develops in the slat cove and a feedback mechanism forms between the slat-cove and slat trailing-edge flow fields.

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.

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.

Navier–Stokes analysis of lift-enhancing tabs on multi-element airfoils

Abstract The flow over multi-element airfoils with flat-plate lift-enhancing tabs was numerically investigated. Tabs ranging in height from 0.25 to 1.25% of the reference airfoil chord were studied near the trailing edge of the main element. The two-dimensional numerical simulation employed an incompressible Navier–Stokes solver using a structured, embedded grid topology. The effects of various tabs were studied at a constant Reynolds number on a two-element airfoil with a slotted flap. Both computed and measured results indicated that a tab in the main-element cove improved the maximum lift and lift-to-drag ratio relative to the baseline airfoil without a tab. Computed streamlines revealed that the additional turning caused by the tab may reduce the amount of separated flow on the flap. A three-element airfoil was also studied over a range of Reynolds numbers, with computed results shown to be in good agreement with experimental data.

Assuring ground-based detect and avoid for UAS operations

One of the goals of the Marginal Ice Zones Observations and Processes Experiment (MIZOPEX) NASA Earth science mission was to show the operational capabilities of Unmanned Aircraft Systems (UAS) when deployed on challenging missions, in difficult environments. Given the extreme conditions of the Arctic environment where MIZOPEX measurements were required, the mission opted to use a radar to provide a ground-based detect-and-avoid (GBDAA) capability as an alternate means of compliance (AMOC) with the see-and-avoid federal aviation regulation. This paper describes how GBDAA safety assurance was provided by interpreting and applying the guidelines in the national policy for UAS operational approval. In particular, we describe how we formulated the appropriate safety goals, defined the processes and procedures for system safety, identified and assembled the relevant safety verification evidence, and created an operational safety case in compliance with Federal Aviation Administration (FAA) requirements. To the best of our knowledge, the safety case, which was ultimately approved by the FAA, is the first successful example of non-military UAS operations using GBDAA in the U.S. National Airspace System (NAS), and, therefore, the first nonmilitary application of the safety case concept in this context.

Simulation of Sweep-Jet Flow Control, Single Jet and Full Vertical Tail

This work is a simulation technology demonstrator, of sweep jet flow control used to suppress boundary layer separation and increase the maximum achievable load coefficients. A sweep jet is a discrete Coanda jet that oscillates in the plane parallel to an aerodynamic surface. It injects mass and momentum in the approximate streamwise direction. It also generates turbulent eddies at the oscillation frequency, which are typically large relative to the scales of boundary layer turbulence, and which augment mixing across the boundary layer to attack flow separation. Simulations of a fluidic oscillator, the sweep jet emerging from a nozzle downstream of the oscillator, and an array of sweep jets which suppresses boundary layer separation are performed. Simulation results are compared to data from a dedicated validation experiment of a single oscillator and its sweep jet, and from a wind tunnel test of a full-scale Boeing 757 vertical tail augmented with an array of sweep jets. A critical step in the work is the development of realistic time-dependent sweep jet inflow boundary conditions, derived from the results of the single-oscillator simulations, which create the sweep jets in the full-tail simulations. Simulations were performed using the computational fluid dynamics (CFD) solver Overow, with high-order spatial discretization and a range of turbulence modeling. Good results were obtained for all flows simulated, when suitable turbulence modeling was used.

Investigation of Tractor Base Bleeding for Heavy Vehicle Aerodynamic Drag Reduction

The drag reduction capability of tractor base bleeding is investigated using a combination of experiments and numerical simulations. Wind tunnel measurements are made on a 1:20 scale heavy vehicle model at a vehicle width-based Reynolds number of 420,000. The tractor bleeding flow, which is delivered through a porous material embedded within the tractor base, is introduced into the tractor-trailer gap at bleeding coefficients ranging from 0.0-0.018 for two different gap sizes with and without side extenders. At the largest bleeding coefficient with no side extenders, the wind-averaged drag coefficient is reduced by a maximum value of 0.015 or 0.024, depending upon the gap size. To determine the performance of tractor base bleeding under more realistic operating conditions, computational fluid dynamics simulations are performed on a full-scale heavy vehicle traveling within a crosswind for bleeding coefficients ranging from 0.0-0.13. At the largest bleeding coefficient, the drag coefficient of the vehicle is reduced by 0.146. Examination of the tractor-trailer gap flow physics reveals that tractor base bleeding reduces the drag by both decreasing the amount of free-stream flow entrained into the gap and by increasing the pressure of the tractor base relative to that of the trailer frontal surface.

Lift-Enhancing Tabs on Swept, Three-Dimensional High-Lift Systems

A three-dimensional high-lift system was computationally simulated to investigate the effectiveness of lift-enhancing tabs on swept wings. The computations were performed by solving the incompressible Navier-Stokes equations on structured, overset grids, and the effects of turbulence were simulated using the one-equation Baldwin-Barth model. Three leading edge sweep angles (0 , 15, 30 deg.) were investigated with and without lift enhancing tabs. The results show that, for the geometry studied, tab effectiveness increases with leading edge sweep angle. Increases in wing lift coefficients of approximately 5%, 27% and 36% were seen for the three sweep angles at ten degrees angle of attack. The computed results for the unswept case are compared with experimental data, and the results from both cases are in agreement.

Visualization of a Sweeping Jet by Laser Speckle Retro-reflective Background Oriented Schlieren

The National Aeronautics and Space Administrations Environmentally Responsible Aviation (ERA) Program is currently investigating the use of sweeping jet actuators as active flow control devices to improve the aerodynamic performances of vertical tails on commercial transporters. Computational Fluid Dynamics (CFD) simulations have shown that the motion of the jet is not a simple sinusoid, but lingers at the extremes of jet deflection. As part of an effort to better understand this non-sinusoidal behavior and validate the CFD, a sweeping jet actuator was tested in the 48-by-32-inch wind tunnel in the Fluid Mechanics Laboratory (FML) at NASA Ames Research Center. The jet was visualized at very high frequencies using a new technique: laser speckle retroreflective background oriented schlieren (RBOS). These measurements confirmed the non-sinusoidal nature of the jet motion. Although measurements were also made by Particle Image Velocimetry (PIV) that resolved the flow velocities in the jet, only the new RBOS technique could provide high enough frequencies to both spatially and temporally resolve the non-sinusoidal motion. This paper presents the laser speckle RBOS method and visualization, as well as a brief comparison to CFD simulations.