The local-correlation laminar-turbulent transition model of Langtry and Menter has seen use over a wide range of fluid dynamic flows. The model is often coupled to two-equation turbulence models via modification to the turbulent kinetic energy equation. A near-wall analysis of turbulent kinetic energy and specific dissipation shows that the coupling of the transition model introduces singular behavior in the turbulent kinetic energy destruction and diffusion terms. This causes the fully turbulent behavior post-transition to deviate from that intended by the shear stress transport model, raising uncertainty in its ability to model relevant turbulent flow physics. An extensively verified Reynolds-averaged Navier–Stokes solver was used to numerically examine the near-wall behavior for a suite of practical test cases, confirming the singular behavior of the destruction term. From the new understanding of the near-wall behavior, a new turbulence index function is derived to detect laminar-turbulent transition for practical aerodynamic configurations. The index is designed such that a value of 0 indicates laminar flow and a value of 1 indicates turbulent flow. Several two-dimensional and three-dimensional test cases were used to test the new turbulence index. The new turbulence index was found to be more reliable and less ambiguous for transition detection in comparison to that designed for use with a shear stress transport model.

Analyzing the Near-Wall Behavior of the Langtry–Menter Transition Model

Assessment of turbulence models for the boundary layer transition flow simulation around a hydrofoil

Aero-optical and aero-heating effects of supersonic turbulent boundary layer with a tangential wall-injection film

Simulations of transition and separation past a wind-turbine airfoil near stall

Measurements, including one-point double, triple or quadruple mean products of velocity fluctuations, have been made in low-speed turbulent, boundary layers on flat surfaces downstream of concave or convex bends with turning angles of 20 or 30 degrees, the length of the curved region being at most 6 times the boundary-layer thickness at entry. These short bends approximate to ‘impulses’ of curvature, and the object of the work was to investigate the impulse response of the boundary layer, essentially the decay of structural changes downstream of the bends. The work can be regarded as a sequel, with much more detailed measurements, to the study by So & Mellor (1972, 1973, 1975) who investigated the response to step increases of curvature: turbulent boundary layers being nonlinear systems, responses to several kinds of curvature history are needed to assemble an adequate description of the flow. The most striking feature of the ‘impulse’ response is that the decay of the high turbulent intensity found at exit from the concave bends is not monotonic; the Reynolds stresses in the outer layer collapse to well below the level at entry, and are still falling slowly at the end of the test rig although in principle they must recover eventually. On the convex (stabilized) side the flow recovers, monotonically in the main, from a low level of turbulent intensity at the exit. The pronounced second-order response on the concave side can be explained qualitatively by interaction between the shear stress and the mean shear and is not peculiar to curved flows, but in the present cases the response is complicated by large changes in the dimensionless structure parameters related to double or triple mean products of velocity fluctuations. Strong spanwise variations, due presumably to longitudinal vortices, further complicate the flow in the concave bends, and decay only very slowly downstream.

The effect of short regions of high surface curvature on turbulent boundary layers

Accuracy, robustness, and efficiency are the three major goals of turbulence closure. Generally, eddy-viscosity models (EVMs) with the Boussinesq approximation are numerically stable and efficient....

Blending the Eddy-Viscosity and Reynolds-Stress Models Using Uniform High-Order Discretization

Accurate and efficient prediction of separated transitional flows is always a big challenge for computational fluid dynamics (CFD), especially in engineering applications. The recently proposed mul...

Guangxue Wang

Papers

Blending the Eddy-Viscosity and Reynolds-Stress Models Using Uniform High-Order Discretization

Blending of Algebraic Transition Model and Subgrid Model for Separated Transitional Flows