Accession Number:

ADA243403

Title:

Observation and Measurements of Flow Structures in the Stagnation Region of a Wing-Body Junction

Descriptive Note:

Technical rept. 1 Dec 1988-31 Aug 1991

Corporate Author:

VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG DEPT OF ENGINEERING SCIENCE AND MECHANICS

Personal Author(s):

• Kim, S.
• Walker, D. A.
• Simpson, R. L.

Report Date:

1991-09-01

Pagination or Media Count:

278.0

Abstract:

Behavior of a junction vortex formed around an obstacle in a boundary layer flow was studied experimentally in a water tunnel for two low speed cases. A wing consisting of a 32 elliptical nose and an NACA 0020 tail was used to simulate the junction vortex. A flow visualization study, using a hydrogen bubble technique, was conducted to investigate flow structures in the stagnation region of the wing. A multiple vortex system showing an acyclic flow pattern was observed. LDV measurements were performed in the plane of symmetry upstream of the wing. The general flow agrees with an earlier wind tunnel test conducted at higher speed. A low frequency, bistable flow structure was observed as in the wind tunnel measurements. The switching between two flow modes a backflow mode and a zero flow mode was analyzed using LDV signals in the zone of a bimodal structure. A dimensionless frequency group was found to represent the average frequency of successive switches from one mode to the other. Visual evidence of an acyclic flow pattern was consistent with LDV measurements and revealed that aperiodic stretching of the junction vortex appears responsible for the bimodal double-peaked structure in the velocity histograms. An attempt to measure the three-dimensional instantaneous velocity field in this region was made. A particle image displacement velocimetry technique was developed using a multiple wire hydrogen bubble method and a high speed video system.

Descriptors:

• *VORTICES
• *FLOW VISUALIZATION
• MEASUREMENT
• HIGH RATE
• REGIONS
• HYDROGEN
• THREE DIMENSIONAL
• LOW VELOCITY
• BUBBLES
• WIND TUNNEL TESTS
• PATTERNS
• FLOW
• VISION
• JUNCTIONS
• WINGS
• VIDEO SIGNALS
• DUAL MODE
• HISTOGRAMS
• WING BODY CONFIGURATIONS
• LOW FREQUENCY
• SWITCHES
• BOUNDARY LAYER FLOW
• WATER TUNNELS
• STAGNATION
• BISTABLE DEVICES
• BACKFLOW
• VELOCITY
• FREQUENCY

Subject Categories:

• Aerodynamics
• Submarine Engineering
• Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE