G. H. Christoph

Bio: G. H. Christoph is an academic researcher from University of Rhode Island. The author has contributed to research in topics: Boundary layer & Turbulence. The author has an hindex of 4, co-authored 8 publications receiving 68 citations.

Prediction of rough-wall skin friction and heat transfer

Abstract: A finite difference solution to the boundary-layer equations for flow over rough surfaces is presented. The boundary-layer equations are cast in a form to account for the blockage effects of roughness elements. The roughness effect is described by a sink term in the momentum equation and a source term in the static enthalpy equation. A two-layer algebraic mixing length model that accounts for low Reynolds numbers, surface roughness, and wall transpiration is developed. Good agreement is shown for several comparisons to rough- wall, flat-plate and sharp-cone data.

A three-dimensional integral method for calculating incompressible turbulent skin friction.

Abstract: A new integral method is proposed for the analysis of three-dimensional incompressible turbulent boundary layers. The method utilizes velocity profile expressions in wall-law form to derive two coupled partial differential equations for the two components of surface skin friction. No shape factors or emprical shear stress correlations are needed in the method. The only requirements are a knowledge of the external velocity and streamline distribution and initial values of skin friction along a starting crossflow line of the flow. The method is insensitive to sidewall conditions and may be continued downstream until the complete three-dimensional separation line of the flow has been computed. Two comparisons with experiment are shown a curved-duct unseparated flow and a T-shaped-box separated flow. The calculations are very straightforward and agree reasonable well with the data for friction, crossflow angle, and separation line.

A simplified approach to the analysis of turbulent boundary layers in two and three dimensions

Abstract: The report deals with a new method of calculation of coupled skin friction and heat transfer in two-dimensional turbulent boundary layers and also with the calculation of axisymmetric and three-dimensional turbulent boundary layers and also with the calculation of axisymmetric and three-dimensional turbulent skin friction. It is based upon an integral approach which assumes analytic law-of-the-wall velocity and temperature profiles through the boundary layer. The new theory is compared to several important experimental studies and the general agreement is good. (Author Modified Abstract)

Perspective: Flow at High Reynolds Number and Over Rough Surfaces—Achilles Heel of CFD

Abstract: The law of the wall and related correlations underpin much of current computational fluid dynamics (CFD) software, either directly through use of so-called wall functions or indirectly in near-wall turbulence models. The correlations for near-wall flow become crucial in solution of two problems of great practical importance, namely, in prediction of flow at high Reynolds numbers and in modeling the effects of surface roughness. Although the two problems may appear vastly different from a physical point of view, they share common numerical features. Some results from the 'super-pipe' experiment at Princeton University are analyzed along with those of previous experiments on the boundary layer on an axisymmetric body to identify features of near-wall flow at high Reynolds numbers that are useful in modeling. The study is complemented by a review of some computations in simple and complex flows to reveal the strengths and weaknesses of turbulence models used in modern CFD methods. Similarly, principal results of classical experiments on the effects of sand-grain roughness are reviewed, along with various models proposed to account for these effects in numerical solutions

Axially symmetric turbulent boundary layers on cylinders: mean velocity profiles and wall pressure fluctuations

Abstract: Experimental measurements of the mean velocity profiles produced by axially symmetric turbulent boundary layers on cylinders of various diameters are described. The profile measurements were made with very small hot wires developed for this investigation. Measurements of the wall shear stress on cylinders ranging from 0.02 to 2.0 in. in diameter are also reported. In the boundary layer on cylinders, well-defined regions exist in which the two-dimensional law of the wall and a three-dimensional wake law are valid. There was no evidence that the boundary layer was not fully turbulent even on the cylinders of smallest diameter. Measurements of wall pressure fluctuations beneath the boundary layer on a 1 in. diameter cylinder are also described. The results were much the same as those previously reported by Willmarth & Yang (1970) for a 3 in. diameter cylinder. The only difference was the discovery that the wall pressure was correlated in the transverse direction approximately half-way around the cylinder. This was not true on the 3 in. diameter cylinder.