Simple Methods for Determining the Virtual Origin of Turbulent Boundary Layers in Hypersonic Flow on Sharp-Edged Flat Plates

1974 ◽  
Vol 41 (3) ◽  
pp. 551-553
Author(s):  
E. J. Hopkins
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Hypersonic Flow ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Boundary Layer Transition ◽  
Simple Relationship ◽  
Flat Plates ◽  
Layer Transition ◽  
Virtual Origin

For hypersonic Mach numbers up to about 8, the virtual origin for turbulent skin-friction calculations is shown to be close to the beginning of boundary-layer transition. A simple relationship between the beginning and end of boundary-layer transition is presented.

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.

An Application of Octant Analysis to Turbulent and Transitional Flow Data

1994 ◽  
Vol 116 (4) ◽  
pp. 752-758 ◽  
Author(s):  
R. J. Volino ◽  
T. 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 processsing 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 are 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 modeling, suggesting the utility of incorporating multiple length scales in transition models.

Flat-Plate Boundary Layers in Accelerated Flow

2016 ◽  
Author(s):  
Pascal Bader ◽  
Manuel Pschernig ◽  
Wolfgang Sanz ◽  
Jakob Woisetschläger ◽  
Franz Heitmeir ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Boundary Layers ◽  
Laser Doppler Anemometry ◽  
Plate Boundary ◽  
Boundary Layer Transition ◽  
Test Case ◽  
Transitional Region ◽  
Layer Transition

Flow in turbomachines is generally highly turbulent. The boundary layers, however, often exhibit laminar-to-turbulent transition. But also relaminarization of the turbulent flow may occur. The state of the boundary layer is important, since it strongly influences transport phenomena like skin friction and heat transfer. It is therefore vitally important for the designer to understand the process of boundary layer transition and to determine the position of transition onset and the length of the transitional region. In order to get into the details of transition and relaminarization it is helpful to study simplified test cases first. Therefore, in this paper a relaminarization test case for a simple geometry is investigated: The boundary layer flow along a flat plate is exposed to acceleration with three different acceleration parameters, which is known as a crucial parameter for relaminarization. Measurements were performed for the inlet free-stream velocities of 5 m/s and 9 m/s. Several experimental techniques for detecting transition were tested at the institute before their application. In this work, Laser-Doppler anemometry (LDA) measurements were performed, since this optical technique is non-intrusive and does not disturb the flow. Therefore it can also be used in narrow flow passages where probe blockage can be crucial. As an outcome of this study, an insight into the process of relaminarization is presented. Although the key onset values for relaminarization stated in literature are fulfilled with the test setup, full relaminarization over the whole boundary layer has not been achieved. It seems, that using only the skin friction as indicator for relaminarization is not sufficient.

scholarly journals Studies on Wake-Disturbed Boundary Layers Under the Influences of Favorable Pressure Gradient and Free-Stream Turbulence: Part I — Experimetal Setup and Discussions on Transition Model

1997 ◽  
Author(s):  
Ken-ichi Funazaki ◽  
Takashi Kitazawa ◽  
Kazuyuki Koizumi ◽  
Tadashi Tanuma
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Test Model ◽  
Flat Plates ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Favorable Pressure Gradient

The objective of this study is to investigate effects of favorable pressure gradient as well as free-stream turbulence upon wake-induced boundary layer transition on a flat plate. Likewise in the previous study by Funazaki (1996), a spoked-wheel type wake generator is employed in this study. Two identical flat plates with sharp edge are used as test model. One of them is for measurement of boundary layers over the test plate by use of a single hot-wire probe, and the other is provided with thin stainless-steel foils on the surface to measure wake-affected heat transfer along the surface. Free-stream turbulence intensities are controlled with several types of turbulence grids. Pressure gradients over the test surface are adjusted by changing an inclination angle of the plate located opposite to the test model. In Part I, transition models proposed by Mayle and Dullenkopf (1990b) and Funazaki (1996a, 1996b) are compared with the experimental data obtained in this study to examine how such a model succeeds or fails in predicting the wake-induced boundary layer transition under the influences of favorable pressure gradient with a low free-stream turbulence.

Unusual boundary-layer transition results on cones in hypersonic flow.

AIAA Journal ◽  
1969 ◽  
Vol 7 (4) ◽  
pp. 660-664 ◽  
Author(s):  
GEORGE G. MATEER ◽  
HOWARD K. LARSON
Keyword(s):  
Boundary Layer ◽  
Hypersonic Flow ◽  
Boundary Layer Transition ◽  
Layer Transition

Boundary Layer Transition Under High Free-Stream Turbulence and Strong Acceleration Conditions: Part 1—Mean Flow Results

1997 ◽  
Vol 119 (3) ◽  
pp. 420-426 ◽  
Author(s):  
R. J. Volino ◽  
T. W. Simon
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Temperature Profiles ◽  
Mean Flow ◽  
Transfer Coefficients ◽  
Mean Velocity ◽  
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 roughly simulate those present on the downstream half of the pressure side of a gas turbine airfoil. Mean velocity and temperature profiles as well as skin friction and heat transfer coefficients are presented. The transition zone is of extended length in spite of the high free-stream turbulence level. Transitional values of skin friction coefficients and Stanton numbers drop below flat-plate, low-free-stream-turbulence, turbulent flow correlations, but remain well above laminar flow values. The mean velocity and temperature profiles exhibit clear changes in shape as the flow passes through transition. 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.

Experimental investigations on characteristics of boundary layer and control of transition on an airfoil by AC-DBD

2018 ◽  
Vol 32 (08) ◽  
pp. 1850108 ◽  
Author(s):  
Xi Geng ◽  
Zhiwei Shi ◽  
Keming Cheng ◽  
Hao Dong ◽  
Qun Zhao ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Boundary Layer Transition ◽  
Plasma Actuators ◽  
Experimental Investigations ◽  
Dbd Plasma ◽  
Layer Transition ◽  
Piv Measurement ◽  
Induced Flow ◽  
And Control

Plasma-based flow control is one of the most promising techniques for aerodynamic problems, such as delaying the boundary layer transition. The boundary layer’s characteristics induced by AC-DBD plasma actuators and applied by the actuators to delay the boundary layer transition on airfoil at Ma = 0.3 were experimentally investigated. The PIV measurement was used to study the boundary layer’s characteristics induced by the plasma actuators. The measurement plane, which was parallel to the surface of the actuators and 1 mm above the surface, was involved in the test, including the perpendicular plane. The instantaneous results showed that the induced flow field consisted of many small size unsteady vortices which were eliminated by the time average. The subsequent oil-film interferometry skin friction measurement was conducted on a NASA SC(2)-0712 airfoil at Ma = 0.3. The coefficient of skin friction demonstrates that the plasma actuators successfully delay the boundary layer transition and the efficiency is better at higher driven voltage.

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.

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