Near-Wall Similarity in a Pressure-Driven Three-Dimensional Turbulent Boundary Layer

Abstract

Interim 14. IX Supplementary Notes_16. "Exte n sive measurements of the mean velocity, wall pressure and wall shear stress fields were Meade in a three-dimensional pressure-driven turbulent boundary layer created by a cylinder with trailing edge placed normal to a flat plate floor.The direct force wall shear stress measurements were made with a unique, floating element direct force sensing shear mater that responded to both the magnitude and direction of the local wall shear stress.These data were used to test the ability of ten near-wall similarity models proposed in the literature to describe the near-wall velocity field for the measured flow under a wiee range of skewing conditions and a variety of pressure gradient and wall shear vector orientations. S. Performing Organization Report Number. Insect if perfotming organization wishes to assign this number.9. Performing Organization Name and Mailing Address. Give name, street, city, state, and zip code. List no more than two levels of an organizational hierarchy. Display the name of the organization exactly as it should appear in Government indexes such as Government Reports Index (GRI).10. Project/ Took/Work Unit Number. Use the project, task and work unit numbers under which the report was prepared.11. Contract/Grant Number. Insert contract or grant number under which report was prepared.12. Sponsoring Agency Name and Mailing Address. Include zip code. C:-e main sponsors.13. Since the majority of documents are multidisciplinary in nature, the primary Field/Group assignment(s) will be the specific discipline, area of human endeavor, or type of physical object. The application(s) will be cross-referenced with secondary Field/Group assignments that will follow the primary posting(s).18. Distribution Statement. Denote public relessabilicy, for example " Release unlimited", or limitation for reasons other than security. Cite any availability to the public, other than NTIS, with address, order number and price, if known. These three-dimensional velocity field, wall pressure field, and wall shear field results were used to test the ability of ten near-wall similarity models proposed in the literature for three-dimensional turbulent boundary layers to describe the near-wall velocity field. Six of these ten models are scalar, treating some form of an equivalent velocity component. Three of the remaining four more complex models are twocomponent vector models and the last is a scalar model which recognizes the vector nature of the near-wall flow by way of a developed velocity.All. of the ten models tested find their origin, directly or indirectly, in an equilibrium boundary layer hy pothesis using a mixing length. there is the problem of fixing a lower y + limit below which data could not be used.If one were to use these three more complex models in a computational scheme replacing the no slip wall boundary condition at the wall with a match to a similarity model near the wall, then for the flows described above, such a match should be made in a range of about 50 < y ...

Turbulence structural changes for a three-dimensional turbulent boundary layer in a 30° bend

“…Although Patel's calibration was developed for a 2DTBL, it was assumed that in 3DTBLs having mild pressure gradients the law of the wall was valid for a distance up to the diameter of the Preston tube. This is consistent with the findings of Pierce, McAllister & Tennant (1983) and Degani, Smith & Walker (1992) on the existence of near-wall similarity in pressure-driven 3DTBLs: see also Olgmen & Simpson (1992) and Flack & Johnston (1993). The measurements were taken with the probe aligned with the mean flow near the wall.…”

Strong vortex/boundary layer interactions

“…The skin friction was estimated by fitting to the logarithmic law of the wall: 1 q+ -ln(y +) + 5.2; 0.41 where According to Pierce et al (1983) this method is accurate to _+ 5-10% for a 3-D boundary layer with a monotonically increasing skew angle up to about 15 ~ The flow yaw angle at the surface (actually, the angle of the skin friction vector) is assumed to be the angle of the flow at the nearest data point to the surface. The probe was nearly parallel with the surface -no special effort was made to align the probe in pitch since the pitch angle in the boundary layer was small.…”

Strong vortex/boundary layer interactions

“…4. However, in the tongue the flow is highly three-dimensional, with large lateral gradients of mean velocity and flow angle variations at a given z as large as 15 ~ Thus, uncertainty in skin friction coefficient here is as high as _4-10% (Pierce et al 1983). Notice also the large lateral velocities above the boundary layer; as shown in Fig.…”