scholarly journals Optimal Design of Passive Flow Control for a Boundary-Layer-Ingesting Offset Inlet Using Design-of-Experiments

2006 ◽  
Author(s):  
Brian Allan ◽  
Lewis Owens ◽  
John Lin
Keyword(s):  
Boundary Layer ◽  
Optimal Design ◽  
Design Of Experiments ◽  
Flow Control ◽  
Passive Flow Control ◽  
Passive Flow

Passive Flow Control on Crossing Shock-Wave/Boundary-Layer Interactions

2019 ◽  
Author(s):  
Matthew J. Schwartz ◽  
Katherine Stamper ◽  
Ryan B. Bond ◽  
John D. Schmisseur
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Flow Control ◽  
Passive Flow Control ◽  
Wave Boundary Layer ◽  
Passive Flow ◽  
Wave Boundary

Boundary Layer Control for a Vertical Axis Wind Turbine Using a Secondary-Flow Path System

2011 ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Archie Raval ◽  
Houston G. Wood ◽  
Paul E. Allaire
Keyword(s):  
Boundary Layer ◽  
Control System ◽  
Flow Control ◽  
Wind Turbine ◽  
Secondary Flow ◽  
Flow Path ◽  
Passive Flow Control ◽  
Passive Flow ◽  
Path System ◽  
Flow Control System

Vertical axis wind turbines (VAWTs) have typically lower efficiency compared to their horizontal counterparts (HAWTs), but are attractive for places where taller structures are prohibited, as well as for regions where available wind speeds are lower. For HAWTs, the blades are always perpendicular to the incoming wind, providing a continuous thrust throughout the rotation. Contrary to HAWTs, VAWTs have advancing blades and retreating blades, where blades backtrack against the wind, causing lower efficiency. Hence, any modifications that can be made to improve the efficiency of VAWTs can be beneficial to the wind industry. Passive flow control permits the airfoil geometry to be modified by means of grooves or slots without requiring heavy mechanisms or actuators. Hence, this form of boundary layer control seems advantageous for wind turbines, so that minimal amount of maintenance is required, while complexity of the turbine is not significantly increased. Such modification changes the boundary layer over an airfoil reducing flow separation and reversed flow. This study introduces a new form of passive flow control: Secondary-flow control system, which works on the principle of mass removal, eliminating flow separation at different apparent angles of attack in a VAWT. CFD analysis is used to investigate passive flow control for the airfoils NACA8H12 and LS0417 in a three-bladed VAWT configuration. A secondary flow path is initially designed and optimized in a single airfoil configuration, and then used to adjust the wind turbine blade design. The effects of secondary-flow control system in a VAWT design configuration are investigated by comparison with the non-modified airfoil design. The CFD results indicate that secondary-flow path system can be used to modify and control the boundary layer for a wind turbine. It is believed that secondary-flow control system incorporated in VAWT design has potential for improving turbine efficiency. Further research should be conducted to optimize the secondary-flow path system according to the shape of the airfoil in a 3D VAWT configuration, so that blades interference can be captured.

scholarly journals Visualization of boundary layer separation and passive flow control on airfoils and bodies in wind-tunnel and in-flight experiments

2012 ◽  
Vol 25 ◽  
pp. 01078
Author(s):  
Lukas Popelka ◽  
Jana Kuklova ◽  
David Simurda ◽  
Natalie Souckova ◽  
Milan Matejka ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Flow Control ◽  
Boundary Layer Separation ◽  
Passive Flow Control ◽  
Layer Separation ◽  
Passive Flow

Passive Flow Control on Low-Pressure Turbine Airfoils

2003 ◽  
Vol 125 (4) ◽  
pp. 754-764 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Free Stream ◽  
Low Pressure ◽  
Suction Surface ◽  
Free Stream Turbulence ◽  
Passive Flow Control ◽  
Low Pressure Turbine ◽  
Passive Flow ◽  
Surface Length

Two-dimensional rectangular bars have been used in an experimental study to control boundary layer transition and reattachment under low-pressure turbine conditions. Cases with Reynolds numbers (Re) ranging from 25,000 to 300,000 (based on suction surface length and exit velocity) have been considered at low (0.5%) and high (8.5% inlet) free-stream turbulence levels. Three different bars were considered, with heights ranging from 0.2% to 0.7% of suction surface length. Mean and fluctuating velocity and intermittency profiles are presented and compared to results of baseline cases from a previous study. Bar performance depends on the bar height and the location of the bar trailing edge. Bars located near the suction surface velocity maximum are most effective. Large bars trip the boundary layer to turbulent and prevent separation, but create unnecessarily high losses. Somewhat smaller bars had no immediate detectable effect on the boundary layer, but introduced small disturbances that caused transition and reattachment to move upstream from their locations in the corresponding baseline case. The smaller bars were effective under both high and low free-stream turbulence conditions, indicating that the high free-stream turbulence transition is not simply a bypass transition induced by the free stream. Losses appear to be minimized when a small separation bubble is present, so long as reattachment begins far enough upstream for the boundary layer to recover from the separation. Correlations for determining optimal bar height are presented. The bars appear to provide a simple and effective means of passive flow control. Bars that are large enough to induce reattachment at low Re, however, cause higher losses at the highest Re. Some compromise would, therefore, be needed when choosing a bar height for best overall performance.

Passive Flow Control on Low-Pressure Turbine Airfoils

2003 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Free Stream ◽  
Low Pressure ◽  
Suction Surface ◽  
Free Stream Turbulence ◽  
Passive Flow Control ◽  
Low Pressure Turbine ◽  
Passive Flow ◽  
Surface Length

Two-dimensional rectangular bars have been used in an experimental study to control boundary layer transition and reattachment under low-pressure turbine conditions. Cases with Reynolds numbers (Re) ranging from 25,000 to 300,000 (based on suction surface length and exit velocity) have been considered at low (0.5%) and high (8.5% inlet) free-stream turbulence levels. Three different bars were considered, with heights ranging from 0.2% to 0.7% of suction surface length. Mean and fluctuating velocity and intermittency profiles are presented and compared to results of baseline cases from a previous study. Bar performance depends on the bar height and the location of the bar trailing edge. Bars located near the suction surface velocity maximum are most effective. Large bars trip the boundary layer to turbulent and prevent separation, but create unnecessarily high losses. Somewhat smaller bars had no immediate detectable effect on the boundary layer, but introduced small disturbances which caused transition and reattachment to move upstream from their locations in the corresponding baseline case. The smaller bars were effective under both high and low free-stream turbulence conditions, indicating that the high free-stream turbulence transition is not simply a bypass transition induced by the free-stream. Losses appear to be minimized when a small separation bubble is present, so long as reattachment begins far enough upstream for the boundary layer to recover from the separation. Correlations for determining optimal bar height are presented. The bars appear to provide a simple and effective means of passive flow control. Bars which are large enough to induce reattachment at low Re, however, cause higher losses at the highest Re. Some compromise would, therefore, be needed when choosing a bar height for best overall performance.

scholarly journals Reynolds-averaged Navier–Stokes modelling in transonic S-ducts with passive flow control

2019 ◽  
Vol 234 (1) ◽  
pp. 31-45
Author(s):  
Tom Hickling ◽  
Grant Ingram
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Transport Model ◽  
Ambient Air ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Engine Operation ◽  
Passive Flow Control ◽  
Passive Flow ◽  
Reynolds Averaged Navier Stokes

S-duct diffusers are used in aircraft with embedded engines to route ambient air to the fan face. Sizing and stealth considerations drive a need for high curvature ducts, but the curvature causes complex secondary flows that lead to total pressure distortion and swirl velocities at the engine face. These must be controlled for stable engine operation. In this paper, tubercles, a novel bio-inspired passive flow control method, are analysed numerically in a duct with transonic flow. The results are compared to experimental data obtained as part of a campaign at the Royal Military College, Canada to investigate the effects of S-duct geometry and novel passive flow control devices on the performance of transonic S-ducts. The performance of Reynolds-averaged Navier–Stokes turbulence models in the S-ducts is assessed – Menter's shear stress transport model predicts excessive losses due to the overactivity of its stress limiter. The realisable k–ɛ model gives a significant improvement in the prediction of static pressure distributions, but losses and distortion characteristics are predicted poorly due to the model's inability to resolve the effects of unsteadiness in separated regions. Large tubercle geometries are found to trigger earlier separation in the centre of the duct by concentrating low momentum fluid in valleys, but they also act as boundary layer fences away from the duct centre. Smaller geometries are found to generate vortices that re-energise the boundary layer, delaying flow separation. Methods are recommended for future computational analyses of S-ducts and new designs of tubercles.

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