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Near-Wall Turbulence and Skin Friction Measurements
Navy SBIR 2006.2 - Topic N06-165 ONR - Ms. Cathy Nodgaard - [email protected] Opens: June 14, 2006 - Closes: July 14, 2006 N06-165 TITLE: Near-Wall Turbulence and Skin Friction Measurements TECHNOLOGY AREAS: Ground/Sea Vehicles ACQUISITION PROGRAM: PMS 450 and DD(X) OBJECTIVE: Enable measurements of steady and unsteady turbulence in the proximity of walls/surfaces at high Reynolds numbers and provide a self-contained skin-friction measurement gauge capability. DESCRIPTION: At high Reynolds number conditions (10 to 1000 million), the important turbulent flow quantities (mean and instantaneous velocities) reside within 10s of microns from the wall. No current system can measure quantities with sufficient accuracy to gain an understanding of the flow (e.g., 3D pressure gradient effects, or wall roughness effects, etc) or to measure the wall skin friction. For design, the resistance is a key component in arriving at a viable propulsion system. For example, the friction drag of ships can, at least in principle, be reduced by the use of some form of lubrication at the hull-water interface. Efforts to explore that possibility are hindered by, inter alia, the lack of a means of making direct measurements of friction drag at points on the hull�s surface. The objective here is to provide a means to understand the near-wall turbulence and to design a gauge that will remedy this deficiency. A somewhat simplified description of the problem is as follows: Assume a free-stream velocities of 35 ms-1 (with a smooth hull), the water in the layer immediately adjacent to the hull (the viscous sub-layer) is moving at a speed, uy, given, roughly, by uy 1.1y, where y is the distance from the hull measured in microns and uy is in ms-1. The shear force imposed on a smooth hull is about 1000 Pa. A capability is needed that can measure the near-wall flow velocities and the stresses directly on the wall. The shear stress device should be flush with the hull. PHASE I: Proof of concept demonstration with variations in Reynolds numbers (as high as 1 million) in a water channel/tunnel for a near-wall turbulence measurement system. For the shear-stress device, the contractor is expected to devise an instrument, and to produce a quantitative analytic description of its performance characteristics, that can be implemented in the form of an insert whose outer surface is flush with the hull and is of approximate dimensions 25 mm in length and 12 mm in width. It must be watertight, and able to withstand pressures of as much as 10 atmospheres. There must be no moving parts except for the strain needed to produce a change in the physical property used to effect the sensing. It is expected that the accuracy would be � 1% or better and that the output would be a digitized sampled data stream. PHASE II: For near-wall measurements, the contractor will develop and demonstrate the turbulence measurement system at high Reynolds numbers (10 million) on a flat plate in a water tunnel/channel and compare results with analytical theory of turbulence, providing mean and unsteady velocities to within 2-5 microns of the surface. For the shear-stress device, the contractor is expected to construct a prototype and demonstrate its properties in a (small) water tunnel. PHASE III: For the near-wall measurement system, the contractor will prepare complete system and user-documentation. For the shear-stress device, it is expected that a successful result will be implemented in a large-scale high-speed measurement program aimed at fully characterizing the merits of various techniques of friction drag reduction. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Turbulent and resistance measurement systems are useful to both air and underwater application communities. This system would provide the unique capability for the commercial and military aircraft, submarine, and ship industries. REFERENCES: 2. Hess DE, Fu TC, Feldman JP. Naval maneuvering research and the need for shear stress measurements. 24th AIAA Aerodynamic Measurement 3. Technology and Ground Testing Conference, 28 Jun-1 July 2004. AIAA 2004-2605. 4. Lauterborn W, Vogel A. Modern optical techniques in fluid mechanics. Ann Rev Fluid Mech 1984;16:223-244. 5. Miles RB, Lempert WR. Quantitative flow visualization in unseeded flows. Ann Rev Fluid Mech 1997;29:285-326. KEYWORDS: turbulence; hydromechanics; underwater measurements; diagnostics; drag reduction; wall roughness; shear stress TPOC: Ronald Joslin
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