Isolated Roughness and Tollmien-Schlichting Waves in Boundary-Layer Transition

2021 ◽  
pp. 193-202
Author(s):  
Shumpei Hara ◽  
Santhosh B. Mamidala ◽  
Jens H. M. Fransson
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Tollmien Schlichting

Numerical simulation of boundary-layer transition and transition control

1989 ◽  
Vol 199 ◽  
pp. 403-440 ◽  
Author(s):  
E. Laurien ◽  
L. Kleiser
Keyword(s):  
Boundary Layer ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Transition Process ◽  
Numerical Results ◽  
Boundary Layer Transition ◽  
Two Dimensional ◽  
Layer Transition ◽  
Longitudinal Vortices ◽  
Tollmien Schlichting

The laminar-turbulent transition process in a parallel boundary-layer with Blasius profile is simulated by numerical integration of the three-dimensional incompressible Navier-Stokes equations using a spectral method. The model of spatially periodic disturbances developing in time is used. Both the classical Klebanoff-type and the subharmonic type of transition are simulated. Maps of the three-dimensional velocity and vorticity fields and visualizations by integrated fluid markers are obtained. The numerical results are compared with experimental measurements and flow visualizations by other authors. Good qualitative and quantitative agreement is found at corresponding stages of development up to the one-spike stage. After the appearance of two-dimensional Tollmien-Schlichting waves of sufficiently large amplitude an increasing three-dimensionality is observed. In particular, a peak-valley structure of the velocity fluctuations, mean longitudinal vortices and sharp spike-like instantaneous velocity signals are formed. The flow field is dominated by a three-dimensional horseshoe vortex system connected with free high-shear layers. Visualizations by time-lines show the formation of A-structures. Our numerical results connect various observations obtained with different experimental techniques. The initial three-dimensional steps of the transition process are consistent with the linear theory of secondary instability. In the later stages nonlinear interactions of the disturbance modes and the production of higher harmonics are essential.We also study the control of transition by local two-dimensional suction and blowing at the wall. It is shown that transition can be delayed or accelerated by superposing disturbances which are out of phase or in phase with oncoming Tollmien-Schlichting instability waves, respectively. Control is only effective if applied at an early, two-dimensional stage of transition. Mean longitudinal vortices remain even after successful control of the fluctuations.

Effects of Weak Free Stream Nonuniformity on Boundary Layer Transition (Keynote Paper)

2003 ◽  
Author(s):  
Jonathan H. Watmuff
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Mean Flow ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Tollmien Schlichting ◽  
Distorted Waves ◽  
Thickness Variations

Experiments are described in which well-defined FSN (Free Stream Nonuniformity) distributions are introduced by placing fine wires upstream of the leading edge of a flat plate. Large amplitude spanwise thickness variations are present in the downstream boundary layer resulting from the interaction of the laminar wakes with the leading edge. Regions of elevated background unsteadiness appear on either side of the peak layer thickness, which share many of the characteristics of Klebanoff modes, observed at elevated Free Stream Turbulence (FST) levels. However, for the low background disturbance level of the free stream, the layer remains laminar to the end of the test section (Rx ≈ l.4×106) and there is no evidence of bursting or other phenomena associated with breakdown to turbulence. A vibrating ribbon apparatus is used to demonstrate that the deformation of the mean flow is responsible for substantial phase and amplitude distortion of Tollmien-Schlichting (TS) waves. Pseudo-flow visualization of hot-wire data shows that the breakdown of the distorted waves is more complex and occurs at a lower Reynolds number than the breakdown of the K-type secondary instability observed when the FSN is not present.

Boundary-layer transition by interaction of discrete and continuous modes

2008 ◽  
Vol 604 ◽  
pp. 199-233 ◽  
Author(s):  
YANG LIU ◽  
TAMER A. ZAKI ◽  
PAUL A. DURBIN
Keyword(s):  
Boundary Layer ◽  
Finite Amplitude ◽  
Secondary Instability ◽  
Boundary Layer Transition ◽  
Length Scale ◽  
Bypass Transition ◽  
Continuous Mode ◽  
Layer Transition ◽  
Boundary Layer Turbulence ◽  
Tollmien Schlichting

The natural and bypass routes to boundary-layer turbulence have traditionally been studied independently. In certain flow regimes, both transition mechanisms might coexist, and, if so, can interact. A nonlinear interaction of discrete and continuous Orr-Sommerfeld modes, which are at the origin of orderly and bypass transition, respectively, is found. It causes breakdown to turbulence, even though neither mode alone is sufficient. Direct numerical simulations of the interaction shows that breakdown occurs through a pattern of Λ-structures, similar to the secondary instability of Tollmien–Schlichting waves. However, the streaks produced by the Orr-Sommerfeld continuous mode set the spanwise length scale, which is much smaller than that of the secondary instability of Tollmien–Schlichting waves. Floquet analysis explains some of the features seen in the simulations as a competition between destabilizing and stabilizing interactions between finite-amplitude distortions.

Numerical and experimental investigations of oblique boundary layer transition

1999 ◽  
Vol 393 ◽  
pp. 23-57 ◽  
Author(s):  
STELLAN BERLIN ◽  
MARKUS WIEGEL ◽  
DAN S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Transition ◽  
Experimental Investigations ◽  
Two Dimensional ◽  
Layer Transition ◽  
Oblique Waves ◽  
Starting Point ◽  
Incompressible Boundary ◽  
Tollmien Schlichting ◽  
Streamwise Streaks

A transition scenario initiated by two oblique waves is studied in an incompressible boundary layer. Hot-wire measurements and flow visualizations from the first boundary layer experiment on this scenario are reported. The experimental results are compared with spatial direct numerical simulations and good qualitative agreement is found. Also, quantitative agreement is found when the experimental device for disturbance generation is closely modelled in the simulations and pressure gradient effects taken into account. The oblique waves are found to interact nonlinearly to force streamwise vortices. The vortices in turn produce growing streamwise streaks by non-modal linear growth mechanisms. This has previously been observed in channel flows and calculations of both compressible and incompressible boundary layers. The flow structures observed at the late stage of oblique transition have many similarities to the corresponding ones of K- and H-type transition, for which two-dimensional Tollmien–Schlichting waves are the starting point. However, two-dimensional Tollmien–Schlichting waves are usually not initiated or observed in oblique transition and consequently the similarities are due to the oblique waves and streamwise streaks appearing in all three scenarios.

scholarly journals Blind disturbance separation and identification in a transitional boundary layer using minimal sensing

2021 ◽  
Vol 927 ◽  
Author(s):  
I. Gluzman ◽  
J. Cohen ◽  
Y. Oshman
Keyword(s):  
Boundary Layer ◽  
Numerical Study ◽  
A Priori ◽  
Boundary Layer Transition ◽  
Linear Stability Theory ◽  
Plasma Actuators ◽  
Flow State ◽  
Layer Transition ◽  
Novel Approach ◽  
Tollmien Schlichting

A novel approach is presented for identifying disturbance sources in wall-bounded shear flows. The underlying approach models the flow state, as measured by sensors embedded in the flow, as a mixture of disturbance sources. The degenerate unmixing estimation technique is adopted as a blind source separation technique to recover the separate sources and their unknown mixing process. The efficiency of this approach stems from its ability to isolate any, a priori unknown, number of sources, using two sensors only. Furthermore, by adding a single additional sensor, the method is expanded to also determine the propagation velocity vector of each of the isolated sources, based on sensor readings from three sensors appropriately located in the flow field. Theoretical guidelines for locating the sensors are provided. The power of the method is demonstrated via computer simulations and wind-tunnel experiments. The numerical study considers disturbances comprising discrete Tollmien–Schlichting waves and wave packets. Linear stability theory is used to model source mixtures acquired by sensors placed in a Blasius boundary layer. The experimental study investigates the flow over a flat plate, with hot wires as sensors, and a loudspeaker and plasma actuators as source generators. Based on numerical and experimental demonstrations, it is believed that the new approach should prove useful in various applications, including active control of boundary layer transition from laminar to turbulent flow.

The control of boundary-layer transition using a wave-superposition principle

1983 ◽  
Vol 137 ◽  
pp. 233-250 ◽  
Author(s):  
Andrew S. W. Thomas
Keyword(s):  
Boundary Layer ◽  
Superposition Principle ◽  
Three Dimensional ◽  
Feedback System ◽  
Boundary Layer Transition ◽  
Single Frequency ◽  
Two Dimensional ◽  
Layer Transition ◽  
Tollmien Schlichting ◽  
Equal Amplitude

An experimental study has been made of the concept of controlling boundary-layer transition by superimposing in the flow Tollmien–Schlichting waves that are of equal amplitude and antiphased to the disturbances that grow and lead to transition. The cases that have been considered are transition arising from a single-frequency two-dimensional disturbance and transition arising from a nonlinear interaction between two waves of different frequency. A feedback system for controlling transition has also been studied. In each case, both hot-wire surveys and flow visualization have shown that it is possible to delay transition but that the flow cannot be restored completely to its undisturbed state. This appears to be a consequence of interactions between the very weak three-dimensional background disturbances in the flow and the primary two-dimensional waves. The implications of these findings in an implementation of the concept are discussed.

Parametric Study of Fluidic Oscillators for Use in Active Boundary Layer Control

2011 ◽  
Author(s):  
Marion Mack ◽  
Reinhard Niehuis ◽  
Andreas Fiala
Keyword(s):  
Boundary Layer ◽  
Parametric Study ◽  
Pressure Ratio ◽  
Pressure Fluctuations ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Pressure Transducers ◽  
Tollmien Schlichting ◽  
Exit Mach Number

A parametric study was conducted to identify the main factors influencing the frequency produced by fluidic oscillators with the goal of using the actuator to trigger boundary layer transition through the excitation of Tollmien Schlichting waves. Test bench conditions were chosen to match the static pressure at the actuation position on the candidate blade profile for a cascade exit Mach number of 0.6 and Reynolds numbers from 60,000 to 200,000. The inlet vs. outlet pressure ratio and the position and geometry of the outlet holes were all varied. Additionally, the effect of the oscillator’s scale and the feedback channel geometry were considered. The flow at the exit was measured using a hot wire, while Kulite pressure transducers were used to measure pressure fluctuations within the device. This paper shows that fluidic oscillators can achieve frequencies of 10 kHz and that the parameters considered play an important role in the performance of these devices.

Revisiting hot-wire anemometer measurement of Tollmien–Schlichting waves on a flat plate

2020 ◽  
Vol 34 (14n16) ◽  
pp. 2040095
Author(s):  
Xianyang Jiang
Keyword(s):  
Boundary Layer ◽  
Electromagnetic Interference ◽  
High Speed ◽  
Boundary Layer Transition ◽  
Hot Wire ◽  
S Wave ◽  
Layer Transition ◽  
S Waves ◽  
Wire Probe ◽  
Tollmien Schlichting

The amplification of Tollmien–Schlichting (T-S) wave plays an important role in the process of boundary-layer transition. This paper investigates the measurement of T-S wave using hot-wire anemometer (HWA) in a wind tunnel. To precisely acquire T-S wave, the vibration of hot-wire probe and the influence of electromagnetic interference (EMI) are considered. By introducing different amplitudes and frequencies of vibration ribbon, the development of T-S waves is obtained. Lift-up of low-speed fluid and downward of high-speed fluid are observed during the transition.

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