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1. The effect of acoustic oscillations on swirl flow characteristics are investigated by using an external acoustic driver. A constant acoustic pressure of 600 Pa was maintained at the exit of the swirler. The experiments were performed for different Strouhal numbers. Fluctuations in axial velocities in the recirculation zone those are much higher than the acoustic velocity was observed. However, no significant change in the tangential velocity was observed. It was seen that the maximum fluctuation amplitude increases with Strouhal number in both low and high acoustic velocity fluctuations regimes. These findings are in confirmation with the findings of Dawson et al. (2005) in their hot flow experiments done with self-excited swirl burners. It was found that the use of vane passage size as the characteristic dimension leads to Strouhal numbers in the range of 0.2 to 0.5, where the axial velocity fluctuations in the recirculation zone are high. The 2D instantaneous vorticity values are reduced in the presence of acoustic oscillations as compared with the case when acoustic oscillations are absent. It was also found that the effect of acoustic oscillations on swirl varied with respect to the phase of the oscillations.
The acoustic oscillations help in delocalizing the vorticity patches, thus enhancing mixing. Increased mixing would promote better combustion, which in turn would excite intense acoustic oscillations due to its unsteadiness. The 3-D mean velocity magnitudes were significantly reduced in the presence of acoustic oscillation, indicating increased mixing.
1. The laser used in the present study is a Nd-YAG twin laser system (Big Sky Laser of Quantel, France Inc., make). The operating wavelength is 532 nm, with energy of 30 mJ per pulse. The repetition rate of a Nd-YAG laser is typically 10 – 20 Hz,
2. An oil seeder generator implementing the Laskin nozzles
3. A full frame interline transfer digital CCD cameras (SensiCam, PCO Imaging, Germany Inc., make with resolution 1024 x 1280 Pixels and PixelFly model, PCO Imaging, Germany Inc., make with resolution of 1360 ´ 1024 pixels.
4. The laser and the camera are synchronized with a sequencer (SequencerV8.0 HardSoft, Germany Inc., make). Seco2004, has been used as an interface program to generate the TTL pulses from the sequencer in a required sequence.
5. The acoustic field was characterized by mapping the acoustic pressure in the test section using piezo-electric transducers (PCB Piezotronics Model number 106B60 with sensitivity of 504.9mv/1psi). Acquired analog signal was converted into digital signal by using 16 bit A/D card (Contec Microelectronics, USA, Inc., make).
6. Scheimpflug Adapter:
7. Group: Combustion Flow Diagnostics Laboratory, Department of Aerospace Engineering, IIT Madras.
8. Supervisors: Dr. R.I. Sujith and Dr. S.R. Chakravarthy
9. Student: Arun Raj E, MS Research Student (2004-2006)
1. The laser used in the present study is a Nd-YAG twin laser system (Big Sky Laser of Quantel, France Inc., make). The operating wavelength is 532 nm, with energy of 30 mJ per pulse. The repetition rate of a Nd-YAG laser is typically 10 – 20 Hz,
2. An oil seeder generator implementing the Laskin nozzles
3. A full frame interline transfer digital CCD cameras (SensiCam, PCO Imaging, Germany Inc., make with resolution 1024 x 1280 Pixels and PixelFly model, PCO Imaging, Germany Inc., make with resolution of 1360 ´ 1024 pixels.
4. The laser and the camera are synchronized with a sequencer (SequencerV8.0 HardSoft, Germany Inc., make). Seco2004, has been used as an interface program to generate the TTL pulses from the sequencer in a required sequence.
5. Group: Combustion Flow Diagnostics Laboratory, Department of Aerospace Engineering, IIT Madras.
6. Supervisors: Dr. R.I. Sujith and Dr. S.R. Chakravarthy
7. Student: Arun Raj E, MS Research Student (2004-2006)
"Download xsec-30mmdownstream - st0.268-no oscillations- camA-Raw Images "
"Download xsec-30mmdownstream - st0.268-no oscillations- camB-Raw Images "
"Download xsec-30mmdownstream - st0.268-Random oscillations- camA-Raw Images "
"Download xsec-30mmdownstream - st0.268-random oscillations- camB-Raw Images "
2. Time-resolved Stereo PIV Measurement of Pulsatile Flow in the Modeled Artery
The aim is to investigate the behavior of pulsatile blood flow in the curved pipe (Fig. 1) that assimilates the Internal Carotid Artery (ICA), which is one of preferential locations of an aneurysm. Since complicated secondary flow arises due to curvature of artery, the PIV (Particle Image Velocimetry) is applied to obtain detailed flow information of in vitro experiments. However, the blood flow in the artery is pulsatile (fig. 2) and time-resolution of the conventional PIV is not enough to capture transient behavior of pulsatile flow. Thus, the time-resolved PIV, which consists of high-speed cameras and high repetition rate lasers, is applied to measure unsteady flow (fig. 3). Since this new measuring method can provide superior resolution in space as well as in time. The resolution in space is also improved from two-dimensional PIV system to stereo PIV system. In order to perform stereo calibration at a narrow and complex measurement area, we developed non-invasive stereo calibration technique using laser beams.
Figure 4 shows the result of 2D time-resolved PIV measurement. The mainstream flow profile changes drastically in flow inside curved pipe due to pulsation. Especially, the separation region is formed during diastole, it turns out that expansion and the reverse flow promotes and more complicated structure is formed. Moreover, the secondary flow pattern at the systole and diastole phases are completely different, and the balance change of the vorticity magnitude relationship between the inner vortex and the outer vortex is very complex.
Figure 5 shows the result of stereo time-resolved PIV measurement, two-dimensional three-components transient flow structure is observed. Pairs of secondary flow vortex have different momentum and they affect each other intricately. The flow characteristics at the systole phase are drastically different from those at the diastole phase even with the same Reynolds number.
Reference paper: I. Oishi, M., Oshima, M. and Kobayashi, T. High-speed PIV Measurement of Blood Flow in the Modeled Artery. Proceedings of PSFVIP-4, Chamonix France, Paper No.F4098, 2003.
II. Oishi, M., Oshima, M. and Kobayashi, T. PIV Measurement of Flow in the Modeled Artery using High Speed Camera. Proceedings of the 7th Asian Symposium on Visualization, Singapore, 2003.
III. Oishi, M., Oshima, M. Saga, T. and Kobayashi, T. Dynamic PIV Measurement of Pulsatile Flow in the Modeled Artery. Proceedings of 11th International Symposium on Flow Visualization, Notre Dame, Indiana, USA, Paper No.099, 2004.
IV. M. Oishi, M. Oshima, Y. Bando, T. Kobayashi, Time-resolved Stereo PIV Measurement of Pulsatile Flow in the Modeled Artery, The 5th Pacific Symposium on Flow Visualization and Image Processing, 2005, Australia, pp. 63-64
Supervisors: Prof. Marie OSHIMA
3. Stereoscopic PIV measurement in cerebral artery model with rigid wall
In this research, we make in vitro model (Fig. 1) that has realistic vessel geometry, and we visualized velocity field in cerebral aneurysm and velocity near the wall using in vitro model at the steady state. And we investigate the distribution of wall shear stress, which plays an important role in formation, growth and rupture of the cerebral aneurysm. To visualize the velocity field and calculate the wall shear stress, we use stereoscopic particle image velocimetry (stereo-PIV)(Fig. 2), to noninvasively measure the flow and obtain the information on three velocity components simultaneously at many points in any plane.
The measurement geometry (Fig. 3(a)) is MCA with cerebral aneurysm at bifurcation area, and we measured 36 slices from near branching to top of aneurysm (Fig. 3(b)).
Because we measured the flow in detail, we can make the 3D velocity map in the aneurysm. So we can make the distribution of velocity form any direction (Fig. 4), we can understand the flow structure intuitively.
We visualized the streamline to investigate the flow structure in the aneurysm (Fig. 5). In these results, the flow mostly goes into the aneurysm rather than into the branching arteries, and two vortices along the aneurysm are observed.
And we calculated the wall shear stress using velocity data and geometry data, which is reconstructed from raw data of the CT angiography (Fig. 6). The value are normalized the averaged wall shear stress at the z=0mm. The result shows that the magnitude of WSS averaged over the aneurysm is lower than that of WSS averaged over the rest of the blood vessels.
Reference paper: I. Y. Akedo, M. Oshima, M. Oishi and T. Saga, Visualization of Flow Structure In Cerebral Aneurysm Model, The 8th Asian Symposium on Visualization, 2005, Thailand, pp. 177-179.
II. Y. Akedo, M. Oshima, M. Oishi , T. Saga and T. Kobayashi, Stereoscopic PIV Measurement in Cerebral Artery Model, Nihon Kikai Gakkai Ronbunshu, B (T-ransactions of the Japan Society of Mechanical Engineers, Series B), 72-722 (2006), 2386-2393.
Supervisors: Prof. Marie OSHIMA
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