An experimental study of a three-dimensional pressure-driven turbulent boundary layer

Abstract

Aerospace and Ocean Engineering (ABSTRACT)A three dimensional, pressure driven turbulent boundary layer created by an idealized wing-body junction flow is experimentally studied. The body used is a 3 : 2 elliptical nosed NACA 0020 tailed symmetric profile which has a chord length of 30.5 cm (12 inches), maximum thickness of 7.17 cm (2.824 inches) , heigth of 22.9 cm (9.016 inches). The body was sitting on a flat plate. The nominal reference velocity of the flow is 27 m/sec and the Reynolds number based on the momentum thickness at 0.75 chord upstream of the body on the centerline of the tunnel is~ 5936. The data presented include time-mean static pressure, skin friction magnitude and direction on the wall, as well as the mean velocity and all Reynolds stresses at several stations on a line dete~ed with the mean velocity vector component parallel to the wall in the layer where the u 2 normal stress is maximum. The mean velocity and stress data were obtained both with hot-wire ( HW ) and laser-Doppler-velocimeter ( LDV ) techniques. The LDV measurements were taken twice due to the differences observed between the HW and LDV data, which is also shown with the present study. This gave a chance to study the uncertainties on the mean velocity and the stresses extensively. Pressure distributions on the wing and the on the bottom plate were obtained with a Scanivalve and an inclined manometer. Skin friction vectors at several locations on the wall were measured in another study done by Allinger ( 1990 ) with a laser interferometer technique. The data show that the eddy viscosity of the flow is not isotropic, but the ratio of eddy viscosities perpendicular and parallel to the direction of the mean velocity vector component parallel to the wall at the point in the layer where u 2 is maximum is close to unity, and the shear-stress vector Several fellow students and research associates need to be thanked. I would like to thank especially to Dr. Naval K. Agarwal for being friendly and helpful, even in personal problems, and to Dr.William J. Devenport for preparing much of the instrumentation that I used in the research.Patience of a good friend, Fei T. Kwok, in proof reading my entire dissertation is unforgettable. I would like to thank to Seungki Ahn, Kevin A. Shinpaugh, and Richard B. Mays for being friends. Figure 59a. N, anisotropy constant computed using LDV data in tunnel coordinates. 254 Figure 59b. N, anisotropy constant computed using LDV data in tunnel coordinates. 255 Figure 59c. N, anisotropy constant computed using LDV data in tunnel coordinates. 256 Figure 60a. N, anisotropy constant computed using LDV data in free-stream coordinates. 257 Figure 60b. N, anisotropy constant computed using LDV data in free-stream coordinates. 258 Figure 60c. N, anisotropy constant computed using LDV data in free-stream coordinates. 259 Figure 6 la. N, anisotropy constant computed using LDV data in maximum normal stress coordinates. Figure 62a. Al, Townsend's structural parameter computed using LDV data. ...

Structure of 2-D and 3-D Turbulent Boundary Layers with Sparsely Distributed Roughness Elements

“…The use of LDV also permits a non-intrusive way of making measurements. The 3-D rough-wall boundary layers is generated by a wing/body junction flow similar to the well documented smooth wall 3-D boundary layers around the wing/body junction (Ölçmen and Simpson, 1995b), the difference being that the body surface around the wing has a distribution of roughness elements. The distributions are the same as those tested in the 2-D rough-wall TBL.…”

“…This basic research is examining the fundamental way in which roughness affects the near-wall behavior of 3-D turbulent boundary layers. This is somewhat different than for 2-D cases because of significant mean and fluctuation flow skewing nearest the wall (Anderson and Eaton, 1989, Schwarz and Bradshaw, 1994, and Ölçmen and Simpson, 1995b. One of the key differences between 2-D and 3-D TBL is the presence of the crossstream velocity gradient ( y W ∂ ∂ ) which is the main contributor to the streamwise vorticity.…”

“…One of the key differences between 2-D and 3-D TBL is the presence of the crossstream velocity gradient ( y W ∂ ∂ ) which is the main contributor to the streamwise vorticity. Measurements carried out in the rough-wall 3-D turbulent boundary layers are at the same locations where Ölçmen and Simpson (1995b) performed their smooth wall measurements. An idealized wing/body junction was used to generate a 3-D pressure driven TBL in its vicinity and measurements were made at seven stations around it.…”

Octant analysis based structural relations for three-dimensional turbulent boundary layers

“…The flow field around this particular wing is extremely well documented; detailed references for the flow data used in this study and data with different approach boundary layer Reynolds numbers are discussed in papers by Ölçmen and Simpson,[11][12][13][14][15] Simpson, 16,17 and references therein. All the Reynolds-averaged data used in this paper, including up to second-order products, the surface pressure measurements, and surface oil-flow visualizations, are presented by Ölçmen et al 12,14 A brief description of the mean flow field and the Reynolds stress distribution is given here to aid in the discussion of the Nagano-Tagawa model.…”

“…All the Reynolds-averaged data used in this paper, including up to second-order products, the surface pressure measurements, and surface oil-flow visualizations, are presented by Ölçmen et al 12,14 A brief description of the mean flow field and the Reynolds stress distribution is given here to aid in the discussion of the Nagano-Tagawa model. In this paper, the data are used as represented in wallstress coordinates where the x axis is along the wall-shearstress direction on the tunnel wall pointing downstream and the y axis is perpendicular to the wall.…”