Experimental Analysis and Prediction of Wake-Induced Transition in Turbomachinery

2004 ◽  
Author(s):  
Witold Elsner ◽  
Stephane Vilmin ◽  
Stanislaw Drobniak ◽  
Wladyslaw Piotrowski
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Leading Edge ◽  
Transition Process ◽  
Full Time ◽  
Blade Profile ◽  
Velocity Fluctuations ◽  
Cambridge University ◽  
Flow Features ◽  
Good Agreement

The paper presents an experimental and numerical analysis of the interaction between wakes and boundary layers on aerodynamic blade profiles. The experiment revealed that incoming wakes interact with boundary layers and cause the significant increase of velocity fluctuations in the boundary layer and in consequence shift the transition zone towards the leading edge. The full time evolution of periodic wake induced transition was reproduced from measurements. The numerical simulation of the flow around the blade profile has been performed with the use of the adaptive grid viscous flow unNEWT PUIM solver with a prescribed unsteady intermittency method (PUIM) developed at Cambridge University, UK. The results obtained give evidence that the turbulence transported within the wake is mainly responsible for the transition process. The applied CFD solver was able to reproduce some essential flow features related to the bypass and wake-induced transitions and the simulations reveal good agreement with the experimental results in terms of localisation and extent of wake-induced transition.

The Nonstationary Behaviour of Stator Profile Boundary Layer Excited by Periodic Upstream Wakes

2002 ◽  
Author(s):  
Witold Elsner ◽  
Drobniak Stanisław
Keyword(s):  
Boundary Layer ◽  
Transition Zone ◽  
Boundary Layers ◽  
Experimental Analysis ◽  
Leading Edge ◽  
Velocity Fluctuations ◽  
Profile Losses

The paper presents an experimental analysis of the interaction between wakes and boundary layers on aerodynamic profiles. The experiment performed on the model linear stator cascade revealed that incoming wakes cause the significant increase of velocity fluctuations in the boundary layer. It was proved that wakes generated upstream the cascade distinctly shift the transition zone towards the leading edge of the profile what results in the increase of profile losses.

Experimental and Theoretical Investigation of the Supersonic Boundary Layer Stability on the Swept Wing

2008 ◽  
Vol 3 (3) ◽  
pp. 34-38
Author(s):  
Sergey A. Gaponov ◽  
Yuri G. Yermolaev ◽  
Aleksandr D. Kosinov ◽  
Nikolay V. Semionov ◽  
Boris V. Smorodsky
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Leading Edge ◽  
Supersonic Boundary Layer ◽  
Mean Flow ◽  
Swept Wing ◽  
Wing Model ◽  
Dimensional Boundary ◽  
The Stability ◽  
Good Agreement

Theoretical and an experimental research results of the disturbances development in a swept wing boundary layer are presented at Mach number М = 2. In experiments development of natural and small amplitude controllable disturbances downstream was studied. Experiments were carried out on a swept wing model with a lenticular profile at a zero attack angle. The swept angle of a leading edge was 40°. Wave parameters of moving disturbances were determined. In frames of the linear theory and an approach of the local self-similar mean flow the stability of a compressible three-dimensional boundary layer is studied. Good agreement of the theory with experimental results for transversal scales of unstable vertices of the secondary flow was obtained. However the calculated amplification rates differ from measured values considerably. This disagreement is explained by the nonlinear processes observed in experiment

Mechanically Amplified Piezoelectric Microactuators for Laminar-Turbulent Transition Control on Airfoils

2009 ◽  
Vol 6 (4) ◽  
pp. 211-218 ◽  
Author(s):  
C. Bolzmacher ◽  
X. Riedl ◽  
J. Leuckert ◽  
M. Engert ◽  
K. Bauer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
High Speed ◽  
Leading Edge ◽  
Transition Process ◽  
Open Loop ◽  
Film Sensor ◽  
Transition Control ◽  
Transitional Boundary Layer ◽  
Tollmien Schlichting

Drag reduction on airfoils using arrays of micro-actuators is one application of so-called Aero-MEMS. These microactuators interact with TS instabilities (Tollmien-Schlichting waves) inside a transitional boundary layer by superimposing artificially generated counterwaves in order to delay the transition process. These actuators need to exhibit a relatively large stroke at relatively high operational frequencies when operated at high Mach numbers. For this purpose, a novel micromachined mechanical amplification unit for increasing the stroke of piezoelectric microactuators up to high frequencies is proposed. The mechanical lever is provided by a sliced nickel titanium membrane. In this work, the actuator is explained in detail and wind tunnel experiments are carried out to investigate the effect of this mechanically amplified piezoelectric microactuator on thin transitional boundary layers. The experiments have been carried out in the transonic wind tunnel facility of the Berlin University of Technology on an unswept test wing with an NACA 0004 leading edge. The effectiveness of the actuator for flow control applications is determined in an open-loop setup consisting of one actuator having a relevant spanwise extension and a microstructured hot film sensor array located downstream. The aerodynamic results at Mach 0.33 are presented and discussed. It is shown that the actuator influences TS wave specific frequencies between 2.5 kHz and 7.4 kHz. The actuator amplitude is large enough to influence a transitional boundary layer significantly without bypassing the natural transition process which makes this type of micromachined actuator a candidate for high speed TS-control.

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 development after a separated region

1998 ◽  
Vol 374 ◽  
pp. 91-116 ◽  
Author(s):  
IAN P. CASTRO ◽  
ELEANORA EPIK
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Turbulence Models ◽  
Separated Flow ◽  
Leading Edge ◽  
Turbulence Structure ◽  
Outer Flow ◽  
Free Stream Turbulence ◽  
Layer Region

Measurements obtained in boundary layers developing downstream of the highly turbulent, separated flow generated at the leading edge of a blunt flat plate are presented. Two cases are considered: first, when there is only very low (wind tunnel) turbulence present in the free-stream flow and, second, when roughly isotropic, homogeneous turbulence is introduced. With conditions adjusted to ensure that the separated region was of the same length in both cases, the flow around reattachment was significantly different and subsequent differences in the development rate of the two boundary layers are identified. The paper complements, but is much more extensive than, the earlier presentation of some of the basic data (Castro & Epik 1996), confirming not only that the development process is very slow, but also that it is non-monotonic. Turbulence stress levels fall below those typical of zero-pressure-gradient boundary layers and, in many ways, the boundary layer has features similar to those found in standard boundary layers perturbed by free-stream turbulence. It is argued that, at least as far as the turbulence structure is concerned, the inner layer region develops no more quickly than does the outer flow and it is the latter which essentially determines the overall rate of development of the whole flow. Some numerical computations are used to assess the extent to which current turbulence models are adequate for such flows.

Investigation of the Laminar-Turbulent Transition of Boundary Layers Disturbed by Wakes

1982 ◽  
Author(s):  
H. Pfeil ◽  
R. Herbst ◽  
T. Schröder
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Transition Process ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Turbulent Spots ◽  
Turbulent Transition ◽  
Time Space ◽  
Favorable Pressure Gradient

The boundary layer transition under instationary afflux conditions as present in the stages of turbomachines is investigated. A model for the transition process is introduced by means of time-space distributions of the turbulent spots during transition and schematic drawings of the instantaneous boundary layer thicknesses. To confirm this model, measurements of the transition with zero and favorable pressure gradient are performed.

Equilibrium-Turbulent Boundary Layer Prediction for a Proposed Prandtl Mixing Length Distribution

1968 ◽  
Vol 10 (5) ◽  
pp. 426-433 ◽  
Author(s):  
F. C. Lockwood
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layers ◽  
Length Distribution ◽  
Momentum Equation ◽  
Turbulent Boundary Layers ◽  
Mixing Length ◽  
Good Agreement

The momentum equation is solved numerically for a suggested ramp variation of the Prandtl mixing length across an equilibrium-turbulent boundary layer. The predictions of several important boundary-layer functions are compared with the equilibrium experimental data. Comparisons are also made with some recent universal recommendations for turbulent boundary layers since the equilibrium experimental data are limited. Good agreement is found between the predictions, the experimental data, and the recommendations.

Experiments in a boundary layer subjected to free stream turbulence. Part 2. The role of TS-waves in the transition process

1994 ◽  
Vol 281 ◽  
pp. 219-245 ◽  
Author(s):  
A. V. Boiko ◽  
K. J. A. Westin ◽  
B. G. B. Klingmann ◽  
V. V. Kozlov ◽  
P. H. Alfredsson
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Small Amplitude ◽  
Free Stream ◽  
Transition Process ◽  
Natural Occurrence ◽  
Free Stream Turbulence ◽  
Onset Of Turbulence ◽  
Tollmien Schlichting

The natural occurrence of Tollmien-Schlichting (TS) waves has so far only been observed in boundary layers subjected to moderate levels of free stream turbulence (Tu < 1%), owing to the difficulty in detecting small-amplitude waves in highly perturbed boundary layers. By introducing controlled oscillations with a vibrating ribbon, it is possible to study small-amplitude waves using phase-selective filtering techniques. In the present work, the effect of TS-waves on the transition is studied at Tu = 1.5%. It is demonstrated that TS-waves can exist and develop in a similar way as in an undisturbed boundary layer. It is also found that TS-waves with quite small amplitudes are involved in nonlinear interactions which lead to a regeneration of TS-waves in the whole unstable frequency band. This results in a significant increase in the number of turbulent spots, which promote the onset of turbulence.

Attached cavitation and the boundary layer: experimental investigation and numerical treatment

1985 ◽  
Vol 154 ◽  
pp. 63-90 ◽  
Author(s):  
J. P. Franc ◽  
J. M. Michel
Keyword(s):  
Boundary Layer ◽  
Leading Edge ◽  
The Body ◽  
Numerical Treatment ◽  
Laminar Separation ◽  
Complete Calculation ◽  
Detachment Criterion ◽  
Continuous Curvature ◽  
The One ◽  
Good Agreement

Attached cavitation on a wall with continuous curvature is investigated on the basis of experiments carried out on various bodies (circular and elliptic cylinders, NACA 16 012 foil). Visualization of the boundary layer by dye injection at the leading edge shows that a strong interaction exists between attached cavitation and the boundary layer. In particular, it is shown that the cavity does not detach from the body at the minimum pressure point, but behind a laminar separation, even in largely developed cavitating flow. A detachment criterion which takes into account this link between attached cavitation and boundary layer is proposed. It consists of connecting a cavitating potential-flow calculation and a boundary-layer calculation. Among all the theoretically possible detachment points, the actual detachment point is chosen to be the one for which the complete calculation predicts a laminar separation just upstream. This criterion, applied to the NACA foil, leads to a prediction which is in good agreement with experimental results.

Prediction and investigation of the turbulent flow over a rotating disk

2000 ◽  
Vol 418 ◽  
pp. 231-264 ◽  
Author(s):  
XIAOHUA WU ◽  
KYLE D. SQUIRES
Keyword(s):  
Boundary Layer ◽  
Rotating Disk ◽  
Shear Stresses ◽  
Normal Velocity ◽  
Streamwise Vortices ◽  
Streamwise Vorticity ◽  
Velocity Fluctuations ◽  
Buffer Region ◽  
The Mean ◽  
Good Agreement

Large-eddy simulation (LES) has been used to predict the statistically three-dimensional turbulent boundary layer (3DTBL) over a rotating disk. LES predictions for six parameter cases were compared to the experimental measurements of Littell & Eaton (1994), obtained at a momentum thickness Reynolds number of 2660. A signal-decomposition scheme was developed by modifying the method of Spalart (1988) to prescribe time-dependent boundary conditions along the radial direction, entrainment towards the disk surface was prescribed by satisfying global mass conservation. Predictions of the mean velocities and r.m.s. fluctuations are in good agreement with data, with the largest discrepancy occurring in the prediction of the wall-normal intensities. The primary and two secondary shear stresses are also in good agreement with the measurements and one-dimensional energy spectra of the velocity fluctuations agree well with established laws, i.e. a −1 slope in the buffer region and −5/3 slope near the edge of the boundary layer.Conditionally averaged velocities provide new evidence in support of the structural model of Littell & Eaton (1994) concerning the interaction of mean-flow three-dimensionality and shear-stress producing structures. Inside the buffer region under strong ejections, the conditionally averaged crossflow (radial) velocity is larger than the unconditioned mean, and the profile conditioned on strong sweeps is smaller than the mean. This is consistent with the notion that streamwise vortices having the same sign as the mean streamwise vorticity, and beneath the peak crossflow location, are mostly responsible for strong sweep events; streamwise vortices with opposite sign as the mean streamwise vorticity promote strong ejections. Comparison of two-point spatial correlations with previous measurements in two-dimensional turbulent boundary layers (2DTBLs) indicates interesting structural similarities, e.g. the correlation of wall pressure and surface-normal velocity fluctuations is an odd function of streamwise separation, being positive downstream and negative upstream. These similarities offer quantitative indirect support to the hypothesis advanced by Littell & Eaton (1994) and Johnston & Flack (1996) that structural models describing 2DTBLs may be employed as a baseline in (equilibrium) 3DTBL structural studies.

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