Effects of Concave Curvature on Boundary Layer Transition Under High Freestream Turbulence Conditions

2003 ◽  
Vol 125 (1) ◽  
pp. 18-27 ◽  
Author(s):  
Michael P. Schultz ◽  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Turbulent Transport ◽  
Boundary Layer Transition ◽  
Transitional Flow ◽  
Turbulent Shear ◽  
Radius Of Curvature ◽  
Freestream Turbulence ◽  
Layer Transition ◽  
Transitional Boundary Layer ◽  
Turbulent Shear Stress

An experimental investigation has been carried out on a transitional boundary layer subject to high (initially 9%) freestream turbulence, strong acceleration (K=ν/Uw2dUw/dx as high as 9×10−6), and strong concave curvature (boundary layer thickness between 2% and 5% of the wall radius of curvature). Mean and fluctuating velocity as well as turbulent shear stress are documented and compared to results from equivalent cases on a flat wall and a wall with milder concave curvature. The data show that curvature does have a significant effect, moving the transition location upstream, increasing turbulent transport, and causing skin friction to rise by as much as 40%. Conditional sampling results are presented which show that the curvature effect is present in both the turbulent and nonturbulent zones of the transitional flow.

Effects of Concave Curvature on Boundary Layer Transition Under High Free-Stream Turbulence Conditions

2001 ◽  
Author(s):  
Michael P. Schultz ◽  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Turbulent Transport ◽  
Boundary Layer Transition ◽  
Transitional Flow ◽  
Turbulent Shear ◽  
Radius Of Curvature ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Turbulent Shear Stress

An experimental investigation has been carried out on a transitional boundary layer subject to high (initially 9%) free-stream turbulence, strong acceleration K=ν/Uw2dUw/dxas high as9×10-6, and strong concave curvature (boundary layer thickness between 2% and 5% of the wall radius of curvature). Mean and fluctuating velocity as well as turbulent shear stress are documented and compared to results from equivalent cases on a flat wall and a wall with milder concave curvature. The data show that curvature does have a significant effect, moving the transition location upstream, increasing turbulent transport, and causing skin friction to rise by as much as 40%. Conditional sampling results are presented which show that the curvature effect is present in both the turbulent and non-turbulent zones of the transitional flow.

Conditional Sampling in a Transitional Boundary Layer Under High Freestream Turbulence Conditions

2003 ◽  
Vol 125 (1) ◽  
pp. 28-37 ◽  
Author(s):  
Ralph J. Volino ◽  
Michael P. Schultz ◽  
Christopher M. Pratt
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Streamwise Velocity ◽  
Turbulent Shear ◽  
Conditional Sampling ◽  
Freestream Turbulence ◽  
Mean Velocity ◽  
Transitional Boundary Layer ◽  
Turbulent Shear Stress ◽  
Order Of Magnitude

Conditional sampling has been performed on data from a transitional boundary layer subject to high (initially 9%) freestream turbulence and strong (K=ν/U∞2dU∞/dx as high as 9×10−6) acceleration. Methods for separating the turbulent and nonturbulent zone data based on the instantaneous streamwise velocity and the turbulent shear stress were tested and found to agree. Mean velocity profiles were clearly different in the turbulent and nonturbulent zones, and skin friction coefficients were as much as 70% higher in the turbulent zone. The streamwise fluctuating velocity, in contrast, was only about 10% higher in the turbulent zone. Turbulent shear stress differed by an order of magnitude, and eddy viscosity was three to four times higher in the turbulent zone. Eddy transport in the nonturbulent zone was still significant, however, and the nonturbulent zone did not behave like a laminar boundary layer. Within each of the two zones there was considerable self-similarity from the beginning to the end of transition. This may prove useful for future modeling efforts.

Boundary Layer Transition Under High Free-Stream Turbulence and Strong Acceleration Conditions: Part 2—Turbulent Transport Results

1997 ◽  
Vol 119 (3) ◽  
pp. 427-432 ◽  
Author(s):  
R. J. Volino ◽  
T. W. Simon
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Turbulent Transport ◽  
Turbulent Heat Flux ◽  
Boundary Layer Transition ◽  
Turbulent Shear ◽  
Turbulent Heat ◽  
Layer Transition ◽  
Free Stream Turbulence

Measurements from heated boundary layers along a concave-curved test wall subject to high (initially 8 percent) free-stream turbulence intensity and strong (K = (ν/U∞2 dU∞/dx, as high as 9 × 10−6) acceleration are presented and discussed. Conditions for the experiments were chosen to simulate those present on the downstream half of the pressure side of a gas turbine airfoil. Turbulence statistics, including the turbulent shear stress, the turbulent heat flux, and the turbulent Prandtl number are presented. The transition zone is of extended length in spite of the high free-stream turbulence level. Turbulence quantities are strongly suppressed below values in unaccelerated turbulent boundary layers. Turbulent transport quantities rise with the intermittency, as the boundary layer proceeds through transition. Octant analysis shows a similar eddy structure in the present flow as was observed in transitional flows under low free-stream turbulence conditions. To the authors’ knowledge, this is the first detailed documentation of a high-free-stream-turbulence boundary layer flow in such a strong acceleration field.

scholarly journals An Application of Octant Analysis to Turbulent and Transitional Flow Data

1993 ◽  
Author(s):  
Ralph J. Volino ◽  
Terrence W. Simon
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Boundary Layer Transition ◽  
Transitional Flow ◽  
Heated Wall ◽  
Turbulent Shear ◽  
Stream Velocity ◽  
Turbulent Heat ◽  
Flat Plates

A technique called “octant analysis” was used to examine the eddy structure of turbulent and transitional heated boundary layers on flat and curved surfaces. The intent was to identify important physical processes that play a role in boundary layer transition on flat and concave surfaces. Octant processing involves the partitioning of flow signals into octants based on the instantaneous signs of the fluctuating temperature, t′; streamwise velocity, u′; and cross-stream velocity, v′. Each octant is associated with a particular eddy motion. For example, u′<0, v′>0, t′>0 is associated with an ejection or “burst” of warm fluid away from a heated wall. Within each octant, the contribution to various quantities of interest (such as the turbulent shear stress, −u′v′, or the turbulent heat flux, v′t′) can be computed. By comparing and contrasting the relative contributions from each octant, the importance of particular types of motion can be determined. If the data within each octant is further segregated based on the magnitudes of the fluctuating components so that minor events are eliminated, the relative importance of particular types of motion to the events that are important can also be discussed. In fully-developed, turbulent boundary layers along flat plates, trends previously reported in the literature were confirmed. A fundamental difference was observed in the octant distribution between the transitional and fully-turbulent boundary layers, however, showing incomplete mixing and a lesser importance of small scales in the transitional boundary layer. Such observations were true on both flat and concave walls. The differences are attributed to incomplete development of the turbulent kinetic energy cascade in transitional flows. The findings have potential application to modelling, suggesting the utility of incorporating multiple length scales in transition models.

Criteria for Boundary Layer Transition

2011 ◽  
Author(s):  
Stefan Becker ◽  
Donald M. McEligot ◽  
Edmond Walsh ◽  
Eckart Laurien
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Turbulence Level ◽  
Two Dimensional ◽  
Freestream Turbulence ◽  
Layer Transition ◽  
Layer Flow

New results are deduced to assess the validity of proposed transition indicators when applied to situations other than boundary layers on smooth surfaces. The geometry employed utilizes a two-dimensional square rib to disrupt the boundary layer flow. The objective is to determine whether some available criteria are consistent with the present measurements of laminar recovery and transition for the flow downstream of this rib. For the present data — the proposed values of thresholds for transition in existing literature that are based on the freestream turbulence level at the leading edge are not reached in the recovering laminar run but they are not exceeded in the transitioning run either. Of the pointwise proposals examined, values of the suggested quantity were consistent for three of the criteria; that is, they were less than the threshold in laminar recovery and greater than it in the transitioning case.

Boundary-Layer Transition in Accelerating Flows With Intense Freestream Turbulence: Part 2—The Zone of Intermittent Turbulence

1992 ◽  
Vol 114 (3) ◽  
pp. 322-332 ◽  
Author(s):  
M. F. Blair
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Transition ◽  
Transitional Region ◽  
Freestream Turbulence ◽  
Intermittent Turbulence ◽  
Adiabatic Wall ◽  
Layer Transition ◽  
Flow Acceleration ◽  
Boundary Layer Turbulence

Hot-wire anemometry was employed to examine the laminar-to-turbulent transition of low-speed, two-dimensional boundary layers for two (moderate) levels of flow acceleration and various levels of grid-generated freestream turbulence. Flows with an adiabatic wall and with uniform-flux heat transfer were explored. Conditional discrimination techniques were employed to examine the zones of flow within the transitional region. This analysis demonstrated that as much as one-half of the streamwise-component unsteadiness, and much of the apparent anisotropy, observed near the wall was produced, not by turbulence, but by the steps in velocity between the turbulent and inter-turbulent zones of flow. Within the turbulent zones u′/v′ ratios were about equal to those expected for equilibrium boundary-layer turbulence. Near transition onset, however, the turbulence kinetic energy within the turbulent zones exceeded fully turbulent boundary-layer levels. Turbulent-zone power-spectral-density measurements indicate that the ratio of dissipation to production increased through transition. This suggests that the generation of the full equilibrium turbulent boundary-layer energy cascade required some time (distance) and may explain the very high TKE levels near onset.

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