You are here

Three-dimensional Measurement of Fluid Density Distribution

Description:

TECHNOLOGY AREA(S): Air Platform

OBJECTIVE: Develop and demonstrate a method of measuring, directly or indirectly, the three-dimensional distribution of turbulent fluid (air) density in wind-tunnel experiments at subsonic, transonic and supersonic conditions.

DESCRIPTION: The structure of the density field in a turbulent air flow directly affects the optical properties of the associated air volume, an effect which can degrade the ability to acquire imagery or propagate a laser through that volume. Traditionally, these optical properties of air have been exploited to obtain qualitative information about the structure of the flow through techniques such as schlieren and shadowgraph photography. Other measurements using small laser beams, Shack-Hartmann wavefront sensors, or Background Oriented Schlieren (BOS) have provided some quantitative measurement of the optical properties; however, these methods generally consist of two-dimensional measurements, representing integrated quantities in the direction of optical propagation. Alternatively, the Planar Laser-Induced Fluorescence (PLIF)[3] method provides instantaneous flow density information in a single plane, similar to particle image velocimetry (PIV) which typically measures velocity in a single plane. Recently, volumetric methods such as plenoptic PIV[2] or tomographic BOS[1] have expanded these diagnostic capabilities to three dimensions. This topic seeks a method and apparatus to characterize the three-dimensional density field, independent of the direction of optical propagation. The resulting characterization of the density field could be used to validate computational fluid dynamics (CFD) simulations and design aerodynamic or flow control mitigations to minimize the effect on optical propagation.

As a reference, the objective instrument should be designed to work in a supersonic blow-down wind-tunnel test section (Mach 2.0, Reynolds number of 4 million per foot) with a 1-square-foot cross-sectional area. The instrument should be capable of resolving fluid density features at least as small as 5 mm within a 100 mm x 50 mm x 12.5 mm volume. The uncertainty of the density measurements should be within 10-15 percent.

PHASE I: Develop the instrument concept and associated analysis techniques. Conduct a laboratory experiment to demonstrate the ability of the instrument concept to measure the instantaneous 3D distribution of density in a turbulent air flow (e.g., an open jet or heated, turbulent flow). Show, through analysis, that the concept can be scaled to practical wind-tunnel applications in Phase II.

PHASE II: Develop and build a prototype instrument. Conduct wind-tunnel experiments (preferably both subsonic and supersonic) to demonstrate the instrument performance. Corroborate the density measurements using established quantitative techniques. Show, through analysis, that the instrument can be scaled to the government application in Phase III. The government application will be similar to the reference case described above with the specific parameters set at the beginning of Phase II.

PHASE III DUAL USE APPLICATIONS: Demonstrate the prototype instrument, or a modified version of it, in a supersonic wind tunnel traceable to the government application specified in Phase II. Deliver the instrument hardware, analysis tools and user documentation to the government.

REFERENCES:

    • Hartmann, U, Adamczuk, R., and Seume, J., "Tomographic Background Oriented Schlieren Applications for Turbomachinery," AIAA Paper 2015-1690.

 

    • Fahringer, T.W., and Thurow, B. S., "Comparing Volumetric Reconstruction Algorithms for Plenoptic-PIV."

 

  • Reid, J. Z., Lynch, K. P., and Thurow, B. S., "Density measurements of a turbulent wake using acetone planar laser-induced fluorescence," AIAA Journal, Vol. 51, No. 4 (2013), pp. 829-839.

KEYWORDS: aero-optics, aero-effects, schlieren, PIV, tomography, holography, flow-diagnostics, planar-laser-induced-florescence, wind-tunnel instrumentation, fluid-dynamics

  • TPOC-1: Carrie Noren
  • Phone: 505-853-2685
  • Email: carrie.noren@us.af.mil
US Flag An Official Website of the United States Government