Wall Shear Stress Direction Research Articles

Experimental study of gas-liquid slug flow in a small-diameter vertical pipe

Experimental investigation of upward gas-liquid slug flow in a vertical pipe in 15 mm ID has been carried out. The electrochemical method which permits the determination of the value and direction of instantaneous wall shear stress as well as the mean and fluctuating components of the liquid velocity is used for measurements. It is shown that the change of the sign of the velocity near the wall usually occurs at the moment of slug passage; the time-averaged wall shear stress at low liquid velocities is significantly lower than the value obtained by means of common prediction methods. The results of measuring of the local void fraction. liquid velocity and components of liquid velocity fluctuations are presented. The time-dependent behavior of the instantaneous hydrodynamic characteristics is described.

A miniature, directional surface-fence gage

NEW, miniature (3.175 mm overall diameter) surfacefence gage was developed to measure simultaneously the magnitude and direction of wall shear stress under threedimensional turbulent boundary layers. This paper describes the design, calibration, and application of the gage.

A Review of Near-Wall Similarity Models in Three-Dimensional Turbulent Boundary Layers

Eleven near-wall similarity models for three-dimensional turbulent boundary layers which have been identified in the literature are reviewed. Each model summary includes a brief review of its derivation, discusses limitations in the derivation, estimates the applicable y+ range, and compares differences among the models. This review of three-dimensional similarity models was developed as part of a larger study which tests the validity of ten of these different models by comparison with experimental data which includes the direct and simultaneous measurement of the local wall shear stress direction and magnitude in a three-dimensional turbulent flow. A direct force measurement of local wall shear stress is necessary to test the local wall shear-shear velocity relationship, τ0 = ρq*2, generally assumed in three-dimensional flows. This review is necessary to acquaint the reader with the similarities and differences among the models tested in companion papers since differences among some of the models are significant, particularly in the coordinate systems of the vector models.

Direct Force Wall Shear Measurements in Pressure-Driven Three-Dimensional Turbulent Boundary Layers

Unique, simultaneous direct measurements of the magnitude and direction of the local wall shear stress in a pressure-driven three-dimensional turbulent boundary layer are presented. The flow is also described with an oil streak wall flow pattern, a map of the wall shear stress-wall pressure gradient orientations, a comparison of the wall shear stress directions relative to the directions of the nearest wall velocity as measured with a typical, small boundary layer directionally sensitive claw probe, as well as limiting wall streamline directions from the oil streak patterns, and a comparison of the freestream streamlines and the wall flow streamlines. A review of corrections for direct force sensing shear meters for two-dimensional flows is presented with a brief discussion of their applicability to three-dimensional devices.

An Omnidirectional Wall Shear Meter

An omnidirectional wall shear meter has been developed which is capable of the direct measurement of both magnitude and direction of wall shear stress. Linearity, resolution, and accuracy have been demonstrated analytically and experimentally by static and dynamic calibration. The floating element device works on the cantilevered beam principle. Eddy current probes, set at right angles to the beam and to each other, sense the magnitude and direction of deflection which can be calibrated against known force loadings. The device is used to measure wall shear stress in three-dimensional flows, and was specifically developed as a means of validating proposed three-dimensional near-wall similarity laws.