scholarly journals Effect of Piezo-Embedded Inverted Flag in Free Shear Layer Wake

Aerospace ◽  
2019 ◽  
Vol 6 (3) ◽  
pp. 33
Author(s):  
Sidaard Gunasekaran ◽  
Grant Ross
Keyword(s):  
Shear Layer ◽  
Oscillation Frequency ◽  
Energy Harvester ◽  
Oscillation Amplitude ◽  
Angle Of Attack ◽  
Lower Surface ◽  
Free Shear Layer ◽  
Polyvinylidene Difluoride ◽  
Image Velocimetry ◽  
Naca 0012

The use of flexible inverted piezo embedded Polyvinylidene Difluoride (PVDF) as a simultaneous energy harvester and as a wake sensor is explored. The oscillation amplitude (characterized by voltage output) and oscillation frequency of the piezo-embedded PDVF was quantified in the wake of a 2D NACA 0012 model and SD7003 model at a Reynolds number of 100,000 and 67,000, respectively. The performance of the sensor was also quantified in the freestream without the presence of the wing. In order to quantify the sensor response to angle of attack and downstream distance, the amplitude and frequency of oscillations were recorded in the wing wake. Increase in angle of attack of the wing resulted in increase in oscillation frequency and amplitude of the PVDF. The results also indicated that the inverted flag configuration performed better in the wake under unsteady conditions when compared to freestream conditions. The results from Particle Image Velocimetry indicated that the wake signature was not affected by the presence of the PVDF in the wake. The root mean square voltage contours in the wake of SD7003 airfoil show remarkable free shear layer wake features such as upper and lower surface stratification and downwash angle which shows the sensitivity of the sensor to the unsteadiness in the wake. The capability of this device to act as a potential energy harvester and as a sensor has serious implications in extending the mission capabilities of small UAVs.

scholarly journals On the Wake Properties of Segmented Trailing Edge Extensions

2018 ◽  
Author(s):  
Sidaard Gunasekaran ◽  
Daniel Curry
Keyword(s):  
Lift Coefficient ◽  
Free Shear Layer ◽  
Structural Vibrations ◽  
Trailing Edge ◽  
Total Drag ◽  
Image Velocimetry ◽  
Effective Angle ◽  
The University ◽  
Naca 0012 ◽  
Low Speed Wind Tunnel

Changes in the amount and the distribution of mean and turbulent quantities in the free shear layer wake of a 2D NACA 0012 airfoil and AR 4 NACA 0012 wing with passive segmented rigid trailing edge (TE) extensions was investigated at the University of Dayton Low Speed Wind Tunnel (UD-LSWT). The TE extensions were intentionally placed at zero degrees with respect to the chord line to study the effects of segmented extensions without changing the effective angle of attack. Force based experiments was used to determine the total lift coefficient variation of hte wing with seven segmented trailing edge extensions distributed across the span. The segmented trailing edge extensions had negligible effect of lift coefficient but showed measurable decrement in sectional and total drag coefficient. Investigation of turbulent quantities (obtained through Particle Image Velocimetry (PIV)) such as Reynolds stress, streamwise and transverse RMS in the wake, reveal a significant decrease in magnitude when compared to the baseline. The decrease in the magnitude of turbulent parameters was supported by the changes in coherent structures obtained through two-point correlations. Apart from the reduction in drag, the lower turbulent wake generated by the extensions has implications in reducing structural vibrations and acoustic tones.

scholarly journals Instability patterns between counter-rotating disks

2003 ◽  
Vol 10 (3) ◽  
pp. 281-288 ◽  
Author(s):  
F. Moisy ◽  
T. Pasutto ◽  
M. Rabaud
Keyword(s):  
Aspect Ratio ◽  
Shear Layer ◽  
Particle Image ◽  
Shear Layer Instability ◽  
Free Shear Layer ◽  
Rotating Disks ◽  
Height Ratio ◽  
Aspect Ratios ◽  
Image Velocimetry ◽  
Local Reynolds Number

Abstract. The instability patterns in the flow between counter-rotating disks (radius to height ratio R/h from 3.8 to 20.9) are investigated experimentally by means of visualization and Particle Image Velocimetry. We restrict ourselves to the situation where the boundary layers remain stable, focusing on the shear layer instability that occurs only in the counter-rotating regime. The associated pattern is a combination of a circular chain of vortices, as observed by Lopez et al. (2002) at low aspect ratio, surrounded by a set of spiral arms, first described by Gauthier et al. (2002) in the case of high aspect ratio. Stability curve and critical modes are measured for the whole range of aspect ratios. From the measurement of a local Reynolds number based on the shear layer thickness, evidence is given that a free shear layer instability, with only weak curvature effect, is responsible for the observed patterns. Accordingly, the number of vortices is shown to scale as the shear layer radius, which results from the competition between the centrifugal effects of each disk.

scholarly journals Effect of Angle of Attack on Airfoil NACA 0012 Performance

2020 ◽  
Vol 5 (1) ◽  
pp. 35-40
Author(s):  
Ali Akbar
Keyword(s):  
Fluid Flow ◽  
Wind Speed ◽  
Wind Tunnel ◽  
Lift Force ◽  
Angle Of Attack ◽  
Lower Surface ◽  
Wind Tunnel Experiments ◽  
A Value ◽  
The Difference ◽  
Naca 0012

Airfoil is an aerodynamic form intended to produce a lift force with the smallest drag force. When an airfoil is passed through a fluid flow that causes interaction between the air flow and the surface, variations in velocity and pressure will occur along the top and bottom surfaces of the airfoil, as well as the front and back of the airfoil. The difference in pressure between the upper and lower surface of the airfoil is what causes the resultant force in the direction perpendicular to the direction of fluid flow, this force is called the lift force (lift). In this experiment NACA 0012 airfoil experiments have been carried out using simple wind tunnel. Experiments were conducted with the aim to determine the effect of the angle of attack on the performance of the NACA 0012 airfoil which then analyzed the lift force of the NACA 0012 airfoil. The variation of the angle of attack used was 0 °, 3 °, 6 °, 9 °, 12 °, and 15 ° and used wind speed of 21.5 m / s. The greatest lift force is obtained at an angle of attack of 9 ° with a value of 0.981 while the largest lifting coefficient with a value of 0.106. The greater the angle of attack the greater the airfoil lift force, but for symmetrical airfoil stall at an angle that is too large

scholarly journals On the Wake Properties of Segmented Trailing Edge Extensions

2018 ◽  
Author(s):  
Sidaard Gunasekaran ◽  
Daniel Curry
Keyword(s):  
Lift Coefficient ◽  
Free Shear Layer ◽  
Structural Vibrations ◽  
Trailing Edge ◽  
Total Drag ◽  
Image Velocimetry ◽  
Effective Angle ◽  
The University ◽  
Naca 0012 ◽  
Low Speed Wind Tunnel

Changes in the amount and the distribution of mean and turbulent quantities in the free shear layer wake of a 2D NACA 0012 airfoil and AR 4 NACA 0012 wing with passive segmented rigid trailing edge (TE) extensions was investigated at the University of Dayton Low Speed Wind Tunnel (UD-LSWT). The TE extensions were intentionally placed at zero degrees with respect to the chord line to study the effects of segmented extensions without changing the effective angle of attack. Force based experiments was used to determine the total lift coefficient variation of hte wing with seven segmented trailing edge extensions distributed across the span. The segmented trailing edge extensions had negligible effect of lift coefficient but showed measurable decrement in sectional and total drag coefficient. Investigation of turbulent quantities (obtained through Particle Image Velocimetry (PIV)) such as Reynolds stress, streamwise and transverse RMS in the wake, reveal a significant decrease in magnitude when compared to the baseline. The decrease in the magnitude of turbulent parameters was supported by the changes in coherent structures obtained through two-point correlations. Apart from the reduction in drag, the lower turbulent wake generated by the extensions has implications in reducing structural vibrations and acoustic tones.

scholarly journals Experimental Investigation of Coherent Vortex Structures in a Backward-Facing Step Flow

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2629
Author(s):  
Fangfang Wang ◽  
Ang Gao ◽  
Shiqiang Wu ◽  
Senlin Zhu ◽  
Jiangyu Dai ◽  
...  
Keyword(s):  
Shear Layer ◽  
Shape Change ◽  
Flow Direction ◽  
Critical Distance ◽  
Vortex Structures ◽  
Free Shear Layer ◽  
Backward Facing Step ◽  
Step Flow ◽  
Image Velocimetry ◽  
Coherent Vortex

Coherent vortex structures (CVS) are discovered for more than half a century, and they are believed to play a significant role in turbulence especially for separated flows. An experimental study is conducted for a pressured backward-facing step flow with Reynolds number (Reh) being 4400 and 9000. A synchronized particle image velocimetry (PIV) system is developed for measurement of a wider range of velocity fields with high resolution. The CVS are proved to exist in the separation-reattachment process. For their temporal evolution, a life cycle is proposed that vortices form in the free shear layer, develop with pairings and divisions and finally shed at the reattachment zone, and sometimes new vortical structures are restructured with recovery of flow pattern. The CVS favor the free shear layer with frequent pairings and divisions particularly at the developing stage around x/h = 2~5 (x: distance from the step in flow direction, h: step height), which may contribute to the high turbulent intensity and shear stress there. A critical distance is believed to exist among CVS, which affects their amalgamation (pairing) and division events. Statistics show that the CVS are well organized in spatial distribution and show specific local features with the flow structures distinguished. The streamwise and vertical diameters (Dx and Dy) and width to height ratio (Dx/Dy) all obey to the lognormal distribution. With increase of Reh from 4400 to 9000, Dx decreases and Dy increases, but the mean diameter (D=0.5 × (Dx + Dy)) keeps around (0.28~0.29) h. As the increase of Reh, the vortical shape change toward a uniform condition, which may be contributed by enhancement of the shear intensity.

Investigation of Unsteady Wake-Separated Boundary Layer Interaction Using Particle-Image-Velocimetry

2007 ◽  
Author(s):  
Og˘uz Uzol ◽  
Xue Feng Zhang ◽  
Alex Cranstone ◽  
Howard Hodson
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Shear Layer ◽  
Particle Image ◽  
Separation Bubble ◽  
Free Shear Layer ◽  
Unsteady Boundary Layer ◽  
Layer Interaction ◽  
Image Velocimetry ◽  
Boundary Layer Interaction

The current paper presents an experimental investigation of the interaction between unsteady wakes and the separated boundary layer on the suction side of an ultra-high-lift low-pressure turbine airfoil. Two-dimensional Particle Image Velocimetry (PIV) measurements of the unsteady boundary layer over the T106C LP turbine profile were performed in a low speed linear cascade facility, at selected phases of passing wakes. The wakes are created by moving cylindrical bars across the inlet of the test section. Various phenomena were investigated such as separation and transition characteristics, vortex structures within the unsteady boundary layer, their interaction and effects on the transition process, the corresponding vortex shedding mechanisms and the unsteady behaviour of the separation bubble due to the wake- boundary layer interaction. The current measurements suggest that rollup vortices are generated as the wake approaches the separated shear layer on the suction surface before the wake centerline starts impinging on the blade. At this instant, the bubble is sufficiently high for the free shear layer to roll up into a vortex and the incoming wake is highly distorted (strained) due to the velocity field within the blade passage, and the turbulence distribution within the wake is not symmetrical. Vortices within the boundary layer, identified using the swirl strength distributions calculated from the eigenvalues of the velocity gradient tensor, seem to be coalescing and forming bigger scale structures, which in turn break up into smaller but higher swirl strength eddies. In between the passing wakes, the separation bubble grows in both in height and length, trying to return to its steady state shape.

scholarly journals On the Wake Properties of Segmented Trailing Edge Extensions

Aerospace ◽  
2018 ◽  
Vol 5 (3) ◽  
pp. 89 ◽  
Author(s):  
Sidaard Gunasekaran ◽  
Daniel Curry
Keyword(s):  
Lift Coefficient ◽  
Free Shear Layer ◽  
Structural Vibrations ◽  
Trailing Edge ◽  
Total Drag ◽  
Image Velocimetry ◽  
Effective Angle ◽  
The University ◽  
Naca 0012 ◽  
Low Speed Wind Tunnel

Changes in the amount and the distribution of mean and turbulent quantities in the free shear layer wake of a 2D National Advisory Committee for Aeronautics (NACA) 0012 airfoil and an AR 4 NACA 0012 wing with passive segmented rigid trailing edge (TE) extensions were investigated at the University of Dayton Low Speed Wind Tunnel (UD-LSWT). The TE extensions were intentionally placed at zero degrees with respect to the chord line to study the effects of segmented extensions without changing the effective angle of attack. Force based experiments were used to determine the total lift coefficient variation of the wing with seven segmented trailing edge extensions distributed across the span. The segmented trailing edge extensions had a negligible effect on the lift coefficient, but showed a measurable decrement in the sectional and total drag coefficient. Investigation of turbulent quantities (obtained through Particle Image Velocimetry (PIV)) such as Reynolds stress, streamwise and transverse root-mean square (RMS) in the wake, reveal a significant decrease in magnitude when compared to the baseline. The decrease in the magnitude of turbulent parameters was supported by the changes in coherent structures obtained through two-point correlations. Apart from the reduction in drag, the lower turbulent wake generated by the extensions has implications in reducing structural vibrations and acoustic tones.

Simply supported FPEDs connected by springs for broadband energy harvesting

2020 ◽  
Vol 64 (1-4) ◽  
pp. 201-210
Author(s):  
Yoshikazu Tanaka ◽  
Satoru Odake ◽  
Jun Miyake ◽  
Hidemi Mutsuda ◽  
Atanas A. Popov ◽  
...  
Keyword(s):  
Energy Harvesting ◽  
Evaluation Method ◽  
Energy Harvester ◽  
Vibrational Energy ◽  
Functional Materials ◽  
Vibration Energy ◽  
Theoretical Evaluation ◽  
Vibration Energy Harvester ◽  
Polyvinylidene Difluoride ◽  
Simply Supported

Energy harvesting methods that use functional materials have attracted interest because they can take advantage of an abundant but underutilized energy source. Most vibration energy harvester designs operate most effectively around their resonant frequency. However, in practice, the frequency band for ambient vibrational energy is typically broad. The development of technologies for broadband energy harvesting is therefore desirable. The authors previously proposed an energy harvester, called a flexible piezoelectric device (FPED), that consists of a piezoelectric film (polyvinylidene difluoride) and a soft material, such as silicon rubber or polyethylene terephthalate. The authors also proposed a system based on FPEDs for broadband energy harvesting. The system consisted of cantilevered FPEDs, with each FPED connected via a spring. Simply supported FPEDs also have potential for broadband energy harvesting, and here, a theoretical evaluation method is proposed for such a system. Experiments are conducted to validate the derived model.

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