Boundary Layer Separation Control With Fluidic Oscillators

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Ciro Cerretelli ◽  
Kevin Kirtley
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Maximum Pressure ◽  
Suction Surface ◽  
Stator Vane ◽  
Average Operating ◽  
Fluidic Actuators ◽  
Layer Flow

Fluidic oscillating valves have been used in order to apply unsteady boundary layer injection to “repair” the separated flow of a model diffuser, where the hump pressure gradient represents that of the suction surface of a highly loaded stator vane. The fluidic actuators employed in this study consist of a fluidic oscillator that has no moving parts or temperature limitations and is therefore more attractive for implementation on production turbomachinery. The fluidic oscillators developed in this study generate an unsteady velocity with amplitudes up to 60% rms of the average operating at nondimensional blowing frequencies (F+) in the range of 0.6<F+<6. These actuators are able to fully reattach the flow and achieve maximum pressure recovery with a 60% reduction of injection momentum required and a 30% reduction in blowing power compared with optimal steady blowing. Particle image velocimetry velocity and vorticity measurements have been performed, which show no large-scale unsteadiness in the controlled boundary layer flow.

Boundary Layer Separation Control With Fluidic Oscillators

2006 ◽  
Author(s):  
Ciro Cerretelli ◽  
Kevin Kirtley
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Maximum Pressure ◽  
Suction Surface ◽  
Stator Vane ◽  
Average Operating ◽  
Fluidic Actuators ◽  
Layer Flow

Fluidic oscillating valves have been used in order to apply unsteady boundary layer injection to repair the separated flow of a model diffuser, where the hump pressure gradient represents that of the suction surface of a highly loaded stator vane. The fluidic actuators employed in this study consist of a fluidic oscillator that has no moving parts or temperature limitations and therefore is more attractive for implementation on production turbomachinery. The fluidic oscillators developed in this study generate an unsteady velocity with amplitudes up to 60% RMS of the average operating at non-dimensional blowing frequencies (F+) in the range 0.6 < F+ < 6. These actuators are able to fully reattach the flow and achieve maximum pressure recovery with a 60% reduction of injection momentum required and a 30% reduction in blowing power compared to optimal steady blowing. PIV velocity and vorticity measurements have been performed that show no large-scale unsteadiness in the controlled boundary layer flow.

On the Periodically Unsteady Interaction of Wakes, Secondary Flow Development, and Boundary Layer Flow in An Annular Low-Pressure Turbine Cascade: An Experimental Investigation

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Martin Sinkwitz ◽  
Benjamin Winhart ◽  
David Engelmann ◽  
Francesca di Mare ◽  
Ronald Mailach
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Boundary Layer Flow ◽  
Measurement Data ◽  
Separated Flow ◽  
Low Pressure ◽  
Experimental Investigations ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Layer Flow

The experimental results reported in this contribution address the time-dependent impact of periodically unsteady wakes on the development of profile and end wall boundary layers and consequently on the secondary flow system. Experimental investigations are conducted on an annular 1.5 stage axial turbine rig at Ruhr-Universität Bochum’s Chair of Thermal Turbomachines and Aeroengines. The object under investigation is a modified T106 profile low-pressure turbine (LPT) stator row at a representative exit flow Reynolds number of 200,000. By making use of an annular geometry instead of a linear cascade, the influence of curvilinear end walls, nonuniform, increasing pitch across the span and radial flow migration can be represented. Incoming wakes are generated by a variable-speed driven rotor equipped with cylindrical bars. Special emphasis is put on the wake-induced recurrent formation, suppression, weakening, and displacement of individual vortices and separated flow regimes. For this, based on a comprehensive set of time-resolved measurement data, the interaction of impinging bar wakes and boundary layer flow and thus separation and its periodic manipulation along the passage end walls and on the blade suction surface are studied within the frequency domain.

On the Periodically Unsteady Interaction of Wakes, Secondary Flow Development and Boundary Layer Flow in an Annular LPT Cascade: Part 1 — Experimental Investigation

2018 ◽  
Author(s):  
Martin Sinkwitz ◽  
Benjamin Winhart ◽  
David Engelmann ◽  
Francesca di Mare ◽  
Ronald Mailach
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Boundary Layer Flow ◽  
Measurement Data ◽  
Separated Flow ◽  
Experimental Investigations ◽  
Suction Surface ◽  
Time Resolved ◽  
Unsteady Interaction ◽  
Layer Flow

The results reported in this two-part — combined experimental and numerical — paper address the time-dependent impact of periodically unsteady wakes on the development of profile and end wall boundary layers and consequently on the secondary flow system. Experimental investigations are conducted on an annular 1.5 stage axial turbine rig at Ruhr-Universität Bochum’s Chair of Thermal Turbomachines and Aeroengines. The object under investigation is a modified T106 profile LPT stator row at a representative exit flow Reynolds number of 200,000. By making use of an annular geometry instead of a linear cascade, the influence of curvilinear end walls, non-uniform, increasing pitch across span and radial flow migration can be represented. Incoming wakes are generated by a variable-speed driven rotor equipped with cylindrical bars. Special emphasis is put on the wake-induced recurrent formation, suppression, weakening and displacement of individual vortices and separated flow regimes. For this, based on a comprehensive set of time-resolved measurement data, the interaction of impinging bar wakes and boundary layer flow and thus separation and its periodic manipulation along the passage end walls and on the blade suction surface are studied within the frequency domain.

The Fluid Dynamics of LPT Blade Separation Control Using Pulsed Jets

2001 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Rolf Sondergaard ◽  
Richard B. Rivir
Keyword(s):  
Boundary Layer ◽  
Duty Cycle ◽  
Separation Bubble ◽  
Vortex Generator ◽  
Boundary Layer Separation ◽  
Skew Angle ◽  
Suction Surface ◽  
Duty Cycles ◽  
Wide Range ◽  
Vortex Generator Jets

The effects of pulsed vortex generator jets on a naturally separating low pressure turbine boundary layer have been investigated experimentally. Blade Reynolds numbers in the linear turbine cascade match those for high altitude aircraft engines and industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets (30 degree pitch and 90 degree skew angle) are pulsed over a wide range of frequency at constant amplitude and selected duty cycles. The resulting wake loss coefficient vs. pulsing frequency data add to previously presented work by the authors documenting the loss dependency on amplitude and duty cycle. As in the previous studies, vortex generator jets are shown to be highly effective in controlling laminar boundary layer separation. This is found to be true at dimensionless forcing frequencies (F+) well below unity and with low (10%) duty cycles. This unexpected low frequency effectiveness is due to the relatively long relaxation time of the boundary layer as it resumes its separated state. Extensive phase-locked velocity measurements taken in the blade wake at an F+ of 0.01 with 50% duty cycle (a condition at which the flow is essentially quasi-steady) document the ejection of bound vorticity associated with a low momentum fluid packet at the beginning of each jet pulse. Once this initial fluid event has swept down the suction surface of the blade, a reduced wake signature indicates the presence of an attached boundary layer until just after the jet termination. The boundary layer subsequently relaxes back to its naturally separated state. This relaxation occurs on a timescale which is 5–6 times longer than the original attachment due to the starting vortex. Phase-locked boundary layer measurements taken at various stations along the blade chord illustrate this slow relaxation phenomenon. This behavior suggests that some economy of jet flow may be possible by optimizing the pulse duty cycle and frequency for a particular application. At higher pulsing frequencies, for which the flow is fully dynamic, the boundary layer is dominated by periodic shedding and separation bubble migration, never recovering its fully separated (uncontrolled) state.

scholarly journals Aspects of Vane Film Cooling With High Turbulence: Part I — Heat Transfer

1997 ◽  
Author(s):  
Forrest E. Ames
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Film Cooling ◽  
Large Scale ◽  
Velocity Ratio ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Stagnation Region ◽  
Film Cooling Effectiveness ◽  
High Turbulence

A four vane subsonic cascade was used to investigate the influence of film injection on vane heat transfer distributions in the presence of high turbulence. The influence of high turbulence on vane film cooling effectiveness and boundary layer development was also examined in part II of this paper. A high level, large scale inlet turbulence was generated for this study with a mock combustor (12 %) and was used to contrast results with a low level (1 %) of inlet turbulence. The three geometries chosen to study in this investigation were one row and two staggered rows of downstream cooling on both the suction and pressure surfaces in addition to a showerhead array. Film cooling was found to have only a moderate influence on the heat transfer coefficients downstream from arrays on the suction surface where the boundary layer was turbulent. However, film cooling was found to have a substantial influence on heat transfer downstream from arrays in laminar regions of the vane such as the pressure surface, the stagnation region, and the near suction surface. Generally, heat transfer augmentation was found to scale on velocity ratio. In relative terms, the augmentation in the laminar regions for the low turbulence case was found to be higher than the augmentation for the high turbulence case. The absolute levels of heat transfer were always found to be the highest for the high turbulence case.

scholarly journals Assessment of inner–outer interactions in the urban boundary layer using a predictive model

2019 ◽  
Vol 875 ◽  
pp. 44-70 ◽  
Author(s):  
Karin Blackman ◽  
Laurent Perret ◽  
Romain Mathis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Predictive Model ◽  
Boundary Layers ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Limited Range ◽  
Rough Wall ◽  
Wall Boundary ◽  
Layer Flow

Urban-type rough-wall boundary layers developing over staggered cube arrays with plan area packing density, $\unicode[STIX]{x1D706}_{p}$, of 6.25 %, 25 % or 44.4 % have been studied at two Reynolds numbers within a wind tunnel using hot-wire anemometry (HWA). A fixed HWA probe is used to capture the outer-layer flow while a second moving probe is used to capture the inner-layer flow at 13 wall-normal positions between $1.25h$ and $4h$ where $h$ is the height of the roughness elements. The synchronized two-point HWA measurements are used to extract the near-canopy large-scale signal using spectral linear stochastic estimation and a predictive model is calibrated in each of the six measurement configurations. Analysis of the predictive model coefficients demonstrates that the canopy geometry has a significant influence on both the superposition and amplitude modulation. The universal signal, the signal that exists in the absence of any large-scale influence, is also modified as a result of local canopy geometry suggesting that although the nonlinear interactions within urban-type rough-wall boundary layers can be modelled using the predictive model as proposed by Mathis et al. (J. Fluid Mech., vol. 681, 2011, pp. 537–566), the model must be however calibrated for each type of canopy flow regime. The Reynolds number does not significantly affect any of the model coefficients, at least over the limited range of Reynolds numbers studied here. Finally, the predictive model is validated using a prediction of the near-canopy signal at a higher Reynolds number and a prediction using reference signals measured in different canopy geometries to run the model. Statistics up to the fourth order and spectra are accurately reproduced demonstrating the capability of the predictive model in an urban-type rough-wall boundary layer.

A Method for the Calculation of 3D Boundary Layers on Practical Wing Configurations

1981 ◽  
Vol 103 (1) ◽  
pp. 104-111 ◽  
Author(s):  
J. P. F. Lindhout ◽  
G. Moek ◽  
E. De Boer ◽  
B. Van Den Berg
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Eddy Viscosity ◽  
Separated Flow ◽  
Laminar Boundary Layers ◽  
Eddy Viscosity Model ◽  
Airplane Wing ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

This paper gives a description of a calculation method for 3D turbulent and laminar boundary layers on nondevelopable surfaces. A simple eddy viscosity model is incorporated in the method. Special attention is given to the organization of the computations to circumvent as much as possible stepsize limitations. The method is also able to proceed the computation around separated flow regions. The method has been applied to the laminar boundary layer flow over a flat plate with attached cylinder, and to a turbulent boundary layer flow over an airplane wing.

Surface Flow Patterns as Visualised by Dust Deposits on the Blades of a Fan

1963 ◽  
Vol 67 (633) ◽  
pp. 589-594 ◽  
Author(s):  
E. T. Hignett ◽  
M. M. Gibson
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Leading Edge ◽  
Surface Flow ◽  
Scale Model ◽  
Flow Visualisation ◽  
Pressure Gradients ◽  
Suction Surface ◽  
Layer Flow ◽  
Dust Deposits

Investigations by one of the authors in connection with the design of a fan for a blower type of wind tunnel showed that regular and repeatable dust patterns occurred on the blades of a one-quarter scale model fan of 18 inches diameter. Dust was deposited on the fan blades along the leading-edge and on the suction surface over an area thought to be the turbulent region of the boundary layer. The introduction of isolated protuberances on the dust free area of a blade gave rise to turbulence wedges in which dust was also deposited and this was interpreted as confirmation of the coincidence of the dust deposits with regions of turbulent boundary-layer flow. These deposits showed the existence of a considerable extent of laminar flow on the suction surface of each blade close to the root, a region where high lift coefficients would be expected with associated adverse pressure gradients. Two-dimensional wind tunnel experiments were made to confirm the interpretation of the observed dust patterns by comparison with the smoke filament and volatile liquid methods of flow visualisation and these are reported in Reference 2.

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