Boundary-Layer Transition and Separation Near the Leading Edge of a High-Speed Turbine Blade

1985 ◽  
Vol 107 (1) ◽  
pp. 127-134 ◽  
Author(s):  
H. P. Hodson
Keyword(s):  
Boundary Layers ◽  
Turbine Blade ◽  
High Speed ◽  
Free Stream ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Initial Development ◽  
Free Stream Turbulence ◽  
Hot Film

The state of the boundary layers near the leading edge of a high-speed turbine blade has been investigated, in cascade, using an array of surface-mounted, constant-temperature, hot-film anemometers. The measurements are interpreted with the aid of inviscid and viscous prediction codes. The effects of Reynolds number, compressibility, incidence, and free-stream turbulence are described. In all cases, the initial development of the boundary layers was extremely complex and, even at design conditions, separation and reattachment, transition and relaminarization were found to occur.

On the design of quiet hypersonic wind tunnels

10.35294/tm57 ◽  
2020 ◽  
Author(s):  
Guillaume Grossir
Keyword(s):  
Boundary Layers ◽  
High Speed ◽  
Free Stream ◽  
Measurement Techniques ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Flow Characterization ◽  
Hypersonic Wind Tunnel ◽  
Design Characteristics

This document presents a thorough literature review on the development of hypersonic quiet tunnels. The concept of boundary layer transition in high-speed flows is presented first. Its consequences on the free-stream turbulence levels in ground facilities are reviewed next, demonstrating that running boundary layers along the nozzle walls must remain laminar for quiet operation. The design key points that enable laminar boundary layers and hypersonic operation with low free-stream noise levels are then identified and discussed. The few quiet facilities currently operating through the world are also presented, along with their design characteristics and performances. The expected characteristics and performances of a European quiet tunnel are also discussed, along with flow characterization methodologies and different measurement techniques. It is finally shown that the required expertise to establish the first European quiet hypersonic wind tunnel is mostly at hand.

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.

scholarly journals The Effect of Wake-Passing and Free-Stream Turbulence on Laminar Gas Turbine Blade Boundary Layers

1993 ◽  
Author(s):  
David Greenblatt
Keyword(s):  
Boundary Layers ◽  
Turbine Blade ◽  
Free Stream ◽  
Leading Edge ◽  
Computational Procedure ◽  
Realistic Model ◽  
Computationally Efficient ◽  
Mean Flow ◽  
Free Stream Turbulence ◽  
Wake Passing

A computational procedure has been developed which accounts for the combined time-mean effect of wake-passing and free-stream turbulence on laminar turbine blade boundary layers. The procedure has the advantage of being computationally efficient as well as providing a realistic model of the unsteady nature of the flow. The procedure yielded the parameter TuReD/σD/2 for characterizing the time-mean flow in the leading edge region and the parameter Γ≡2T~u2σx/γ for describing the flow downstream of the stagnation point. A provisional comparison with stagnation flow experimental data showed that the procedure may be more general than initially expected.

Boundary Layer Transition at High Levels of Free Stream Turbulence

1998 ◽  
Author(s):  
Masaharu Matsubara ◽  
P. Henrik Alfredsson ◽  
K. Johan A. Westin
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Turbine Blades ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Flow Visualisation ◽  
Mean Flow ◽  
Layer Transition ◽  
Free Stream Turbulence

Transition to turbulence in laminar boundary layers subjected to high levels of free stream turbulence (FST) can still not be reliably predicted, despite its technical importance, e.g. in the case of boundary layers developing on gas turbine blades. In a series of experiments in the MTL-wind tunnel at KTH the influence of grid-generated FST on boundary layer transition has been studied, with FST-levels up to 6%. It was shown from both flow visualisation and hot-wire measurements that the boundary layer develops unsteady streaky structures with high and low streamwise velocity. This leads to large amplitude low frequency fluctuations inside the boundary layer although the mean flow is still close to the laminar profile. Breakdown to turbulence occurs through an instability of the streaks which leads to the formation of turbulent spots. Accurate physical modelling of these processes seems to be needed in order to obtain a reliable prediction method.

Bypass Transition Modelling: A New Method Which Accounts for Free-Stream Turbulence Intensity and Length Scale

2000 ◽  
Author(s):  
Paul E. Roach ◽  
David H. Brierley
Keyword(s):  
Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Test Surface ◽  
Length Scale ◽  
Pressure Gradients ◽  
Layer Transition ◽  
Free Stream Turbulence

The publication of the present authors’ boundary layer transition data in 1992 (now widely known as the ERCOFTAC test case T3) has led to a spate of new experimental and modelling efforts aimed at improving our understanding of this problem. This paper describes a new method of determining boundary layer transition with zero mean pressure gradient. The approach examines the development of a laminar boundary layer to the start of transition, accounting for the influences of free-stream turbulence and test surface geometry. It is presented as a “proof of concept”, requiring a significant amount of work before it can be considered as a practically applicable model for transition prediction. The method is based upon one first put forward by G.I. Taylor in the 1930’s, and accounts for the action of local, instantaneous pressure gradients on the developing laminar boundary layer. These pressure gradients are related to the intensity and length scale of turbulence in the free-stream using Taylor’s simple isotropic model. The findings demonstrate the need to account for the separate influences of free-stream turbulence intensity and length scale when considering the transition process. Although the length scale has less of an effect than the intensity, its influence is, nevertheless, significant and must not be overlooked. This fact goes a long way towards explaining the large scatter to be found in simple correlations which involve only the turbulence intensity. Intriguingly, it is demonstrated that it is the free-stream turbulence at the leading edge of the test surface which is important, not that found locally outside the boundary layer. The additional influence of leading edge geometry is also shown to play a major role in fixing the point at which transition begins. It is suggested that the leading edge geometry will distort the incident turbulent eddies, modifying the effective “free-stream” turbulence properties. Consequently, it is shown that the scale of the eddies relative to the leading edge thickness is a further important parameter, and helps bring together a large number of test cases.

Relation Between Disturbance of Boundary Layer and Free Stream Turbulence Component

2011 ◽  
Author(s):  
Ryohei Norimatsu ◽  
Shogo Takai ◽  
Masaharu Matsubara
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Plate Boundary ◽  
Prediction Method ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Experimental Investigations ◽  
Major Step ◽  
Layer Transition ◽  
Free Stream Turbulence

In a flat plate boundary layer subjected to isotropic free stream turbulence of few percents turbulence intensity, the streaks, which longitudinally elongated regions of high and low streamwise velocity, appear in the boundary layer and then break down to turbulent spots. Experiments and DNS have revealed that the profile of the streamwise fluctuation energy has a peak at the middle of boundary layer and that the disturbance grows in proportion to the streamwise distance from the leading edge. These results were in good agreement with the non-modal theory. Though the theory suggested that in lower free stream turbulent case modal disturbance has chance to develop and breakdown to turbulence, experimental investigations have not clarified the maximum intensity of the free stream turbulence at which the modal disturbance triggers transition. It is know that there are other processes of the boundary transition that start with a short streak breakdown. In this study various types of the free stream turbulence including anisotropic turbulence are scrutinized using turbulence grids and their relation to the disturbance growth in the boundary layer is investigated. The result with hot-wire measurements shows that the spanwise spectra of the free stream turbulence are essential factor for the non-modal growth. This would be a major step for developing prediction method of boundary layer transition.

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.

The Effect of Wake-Passing and Free-Stream Turbulence on Laminar Gas Turbine Blade Boundary Layers

1994 ◽  
Vol 116 (3) ◽  
pp. 384-391 ◽  
Author(s):  
D. Greenblatt
Keyword(s):  
Boundary Layers ◽  
Turbine Blade ◽  
Free Stream ◽  
Leading Edge ◽  
Computational Procedure ◽  
Realistic Model ◽  
Computationally Efficient ◽  
Mean Flow ◽  
Free Stream Turbulence ◽  
Wake Passing

A computational procedure has been developed that accounts for the combined time-mean effect of wake-passing and free-stream turbulence on laminar turbine blade boundary layers. The procedure has the advantage of being computationally efficient as well as providing a realistic model of the unsteady nature of the flow. The procedure yielded the parameter TuReD/σD/2 for characterizing the time-mean flow in the leading edge region and the parameter Γ (≡ 2T˜Tu2σx/γ) for describing the flow downstream of the stagnation point. A provisional comparison with stagnation flow experimental data showed that the procedure may be more general than initially expected.

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.

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