This website presents a review of several theoretical and experimental results dealing with boundary layers formed by fluid moving along a wall. Topics include a new boundary layer velocity peaking model for mass and momentum conservation, a new simple explanation of aerodynamic lift using the peaking model, and a review of the integral moment method for describing boundary layer thickness and shape. Additional topics are summarized below. The different topics are meant to be standalone although there is some interconnection and references between chapters. The topics are not meant to be an exhaustive examination of boundary layer theory but instead are a summary of the work the author, David Weyburne, conducted while working as a civilian researcher at the United States Air Force Research Laboratory. The work primarily deals with the basic theory and conceptual models for boundary layer flow. Be forewarned that this is not a simple review of boundary layer theory found in the literature. The work is a direct challenge to a number of basic theory and conceptual models existing in the present-day boundary layer literature. Most of the challenges come in a manner that is relatively easy for the reader to verify. To further encourage the reader to verify the enclosed work, an Appendix is added to take the reader through the process of setting up and doing their own fluid flow simulations. An e-book version of the website has been published and is available for free as ISBN: 978-0-578-98334-9 and a PDF version is availible here.

In the Boundary Layer Concept Chapter, the traditional boundary layer concept is reviewed and found to be deficient in that it does not describe boundary layer flow in a way that permits a complete accounting of the excess mass and momentum diverted around an aerodynamically thick object such as a wing. As a remedy, a new conceptual model in which the velocity profiles show near wall peaks is introduced which, when combined with the moment-based boundary layer thickness approach, provides a theoretical path to aerodynamic lift. A preliminary exploration of lift using the new concept is provided. A YouTube video outlining this chapter is available here.

A graphical explanation for aerodynamic lift is presented in the Aerodynamic Lift Chapter. The intent is to provide a simplified explanation of lift based on the conservation of mass, momentum, and energy equations. To understand the forces resulting in lift in terms of mass and momentum conservation, a series of velocity profile plots along a wing are examined. The velocity profiles show peaking behavior in the near wing region. The momentum equation tells us that the resulting velocity changes must be accompanied by pressure changes. The pressure changes for airflow along a wing are shown to result in lower pressure above the wing thereby generating aerodynamic lift. A YouTube video outlining this chapter is available here.

In the Boundary Layer Thickness and Shape Chapter, the new integral moment method for describing the thickness and shape of the fluid boundary layer is outlined. The method can be applied to the velocity profile, thermal profile, inertial profile, and pressure gradient profiles. Some new results and applied applications are included. In one application, laminar to turbulent experimental profiles are shown to display evidence of the ‘streaks’ or ‘puffs’ postulated in the bypass transition model. A YouTube video outlining this chapter is available here.

In the New Blasius Chapter, the Blasius theoretical model is re-examined. Channel flow CFD simulations are used to explore interior and exterior laminar flat plate flow. It is found that the often-used ploy of setting up a wind tunnel into a known Blasius flow condition is flawed. In contrast, using the new boundary layer conceptual model, exterior laminar flow on a thin plate is found to be naturally described as Blasius flow.

In the y-Momentum Equation Chapter, the Falkner-Skan solution obtained from the x‑momentum equation is used to generate equations for the normal to the flow direction boundary layer y‑pressure gradient, dP/dy, using the y‑momentum equation.

In the Boundary Layer Similarity Chapter, a mathematical proof is offered that indicates the displacement thickness and the velocity at the boundary layer edge must be similarity scaling parameters for the velocity profile in any 2-D fluid bounded boundary layer flow. New results are presented that indicate that the momentum thickness must also be a similarity length scale. The thermal boundary layer similarity scaling parameters are found using the same approach.

In the Turbulent Boundary Layer (TBL) Similarity Chapter, the fluid flow community's pursuit of TBL velocity profile similarity is found to be deeply flawed. Early theoretical work regarding the identity of the velocity scaling parameter has been rejected, without explanation or justification, and other scaling parameters have been pursued instead. The problem with using these alternative velocity scaling parameters, such as the Zagarola-Smits scaling parameter, is discussed in detail.

In the Origin of the Logarithmic Law of the Wall: A New TBL Structural Model Chapter, a new turbulent boundary layer conceptualization is introduced that also explains the origin of the Logarithmic Law of the Wall. The new model returns to the simple viscous and inertial two-layer model replacing the current four-layer model, a model based on pure conjecture and unverifiable. To demonstrate the difference between the new model and the present model, the ongoing debate on whether pipe and channel flow Log Law regions at high Reynolds number are identical is revisited. Finally, a new updated physical model of the turbulent boundary layer as an ensemble of Gaussian-like second derivative velocity profiles is proposed and shown to have the right behavior for the turbulent boundary layer.

In the Prandtl Plus Scaling Chapter, a new inner region scaling parameter set is compared to the Prandtl Plus set. It is not a simple case of one set replacing another. The Prandtl Plus set still has a useful application for obtaining wall shear stress approximate values from wind tunnel velocity profile data sets. However, for all other applications, the new inner region parameter set based on the integral moment method appears to be superior. A YouTube video on this subject is available here.

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Acknowledgment

The work described herein was accomplished on behalf of the Air Force Research Laboratory and the support of the Air Force Office of Scientific Research (Gernot Pomrenke).

Version June 2022