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This is an experimental and theoretical research on the motion of buoyant particles in the flow of a free-surface vortex at moderate to high particle Reynolds numbers., Sanitary Engineering

This is an experimental and theoretical research on the motion of buoyant particles in the flow of a free-surface vortex at moderate to high particle Reynolds numbers., Sanitary Engineering

We report on a study of the impact of coherent helical vortex structures on the shape of the reaction zone and heat release in swirling methane/air flames in regimes with a vortex breakdown. Three kinds of atmospheric flames are considered, viz., fuel-lean and fuel-rich premixed flames and a partially premixed fuel-rich lifted flame. Based on the measurements of the velocity fields by a stereo PIV in combination with the OH PLIF and HCHO PLIF, the impact of the coherent flow structures on large-scale corrugations of the reaction zone is evaluated. Helical vortex structures, detected in both the non-reacting and reacting high-swirl flows by using proper orthogonal decomposition, are found to promote combustion both in the lean premixed and fuel-rich partially premixed flames. In the first case, based on the phase-averaged intensity of the HCHO×OH signal and the location of the helical vortex structure in the inner mixing layer, it is concluded that the vortex locally increases the heat release rate by enlarging the flame front and enhancing the mass exchange between the combustion products inside the recirculation zone and the fresh gases. The events of the local flame extinctions are detected in the instantaneous PLIF snapshots for the lean mixture, but they do not cause extinction of the entire flame or a blow-off. In case of the lifted flame, the outer helical vortex structure promotes combustion by locally intensifying the mass exchange between the fuel-rich jet with the surrounding air., Accepted Author Manuscript, ChemE/Transport Phenomena

We report on a study of the impact of coherent helical vortex structures on the shape of the reaction zone and heat release in swirling methane/air flames in regimes with a vortex breakdown. Three kinds of atmospheric flames are considered, viz., fuel-lean and fuel-rich premixed flames and a partially premixed fuel-rich lifted flame. Based on the measurements of the velocity fields by a stereo PIV in combination with the OH PLIF and HCHO PLIF, the impact of the coherent flow structures on large-scale corrugations of the reaction zone is evaluated. Helical vortex structures, detected in both the non-reacting and reacting high-swirl flows by using proper orthogonal decomposition, are found to promote combustion both in the lean premixed and fuel-rich partially premixed flames. In the first case, based on the phase-averaged intensity of the HCHO×OH signal and the location of the helical vortex structure in the inner mixing layer, it is concluded that the vortex locally increases the heat release rate by enlarging the flame front and enhancing the mass exchange between the combustion products inside the recirculation zone and the fresh gases. The events of the local flame extinctions are detected in the instantaneous PLIF snapshots for the lean mixture, but they do not cause extinction of the entire flame or a blow-off. In case of the lifted flame, the outer helical vortex structure promotes combustion by locally intensifying the mass exchange between the fuel-rich jet with the surrounding air., Accepted Author Manuscript, ChemE/Transport Phenomena

Stereoscopic particle imaging velocimetry (Stereo PIV) was utilized to investigate the velocity field and flow structure of a single flexible compressor blade around the wing tip as the angle of attach increased from AOA=0° to AOA=12°. Vortex-induced vibration of blade relieves the deviation of wake central line and reduces the velocity loss of mean streamwise velocity at AOA=10° & 12° in the section of H=145mm. Moreover, the blade vibration greatly strengthens the turbulence intensity of velocity field in the near wake. The transformation of vortex structure due to the self-excited vibration of blade leads to these changes of velocity characteristic. In the results of flow visualization and Λci, a single vortex street with clockwise sense emerges at AOA=4° & 6° and breaks down at AOA≈8°. When vortex-induced vibration of blade model occurs at AOA=10°, many of tiny coherent vortexes form inside the wing tip vortex. At the same time, a new dual vortex street composed by opposite-sign vortex pair replaces the single vortex street in the near weak.

The turbulence dissipation rate and turbulence shear stress are estimated inside a cylindrical, stirred flow mixer by carrying out Stereo PIV measurements in twelve vertical and three horizontal planes. The flow domain is vertically oriented, filled with the water. A commercially-available, three-blade impeller, HR-100, is used as the agitator. The impeller is mounted near the tip of a thin, rigid shaft, which is aligned along the central axis of the flow domain. The impeller rotates with the constant angular speed of 150RPM, and the Reynolds number based on the impeller diameter and the blade's tip-velocity is equal to 59400. The turbulence statistics in the vertical measurement planes are reported before (Shekhar C, Nishino K, Yamane Y and Huang J, “Stereo-PIV measurement of turbulence characteristics in a flow mixer” Journal of Visualization 15 (2012) pp.293~308), which revealed that the rotation induces a downward, as well as tangential, bulk flow motion, which convects the turbulence generated at the blade-water interface, causing the turbulence level below the impeller to be much higher than the level above it. The present study is the second part of the same project, and reports the turbulence statistics in the horizontal measurement planes. The results show that the turbulence level is high in the area swept by the rotating impeller blades and underneath. However, in the outside region, the turbulence damps down and becomes negligible. The vertical and horizontal measurement results are also combined to estimate the production, convection, viscous diffusion, and turbulence dissipation terms of the turbulence kinetic energy's budget equation, along with the turbulence shear stress, along the lines where the different vertical and horizontal planes intersect.

The turbulence dissipation rate and turbulence shear stress are estimated inside a cylindrical, stirred flow mixer by carrying out Stereo PIV measurements in twelve vertical and three horizontal planes. The flow domain is vertically oriented, filled with the water. A commercially-available, three-blade impeller, HR-100, is used as the agitator. The impeller is mounted near the tip of a thin, rigid shaft, which is aligned along the central axis of the flow domain. The impeller rotates with the constant angular speed of 150RPM, and the Reynolds number based on the impeller diameter and the blade's tip-velocity is equal to 59400. The turbulence statistics in the vertical measurement planes are reported before (Shekhar C, Nishino K, Yamane Y and Huang J, “Stereo-PIV measurement of turbulence characteristics in a flow mixer” Journal of Visualization 15 (2012) pp.293~308), which revealed that the rotation induces a downward, as well as tangential, bulk flow motion, which convects the turbulence generated at the blade-water interface, causing the turbulence level below the impeller to be much higher than the level above it. The present study is the second part of the same project, and reports the turbulence statistics in the horizontal measurement planes. The results show that the turbulence level is high in the area swept by the rotating impeller blades and underneath. However, in the outside region, the turbulence damps down and becomes negligible. The vertical and horizontal measurement results are also combined to estimate the production, convection, viscous diffusion, and turbulence dissipation terms of the turbulence kinetic energy's budget equation, along with the turbulence shear stress, along the lines where the different vertical and horizontal planes intersect.

Turbulent swirl flow field in a circular pipe behind the axial fan of specified geometry has been investigated in this paper. The length of the test rig is 27.74D, where D=0.4 m is the average inner pipe diameter. Laser-based measuring techniques, such as stereo particle image velocimetry (SPIV) and laser Doppler anemometry (LDA) were applied in this investigation. Experiments were performed in two sections, behind the axial fan at the position 3.35D from the test rig inlet and downstream at the position 26.31D. The SPIV measurements were performed in the specified cross-sections of the region size of 200x90 mm with the center in the pipe axis and vertical meridian sections of 140x85 mm in size with the center in the pipe axis. Anisotropy of the turbulent velocity field, with the focus on the vortex core region and shear layer, was related to the mean velocity fields. Complex mechanisms in this fluid flow were investigated on the basis of turbulence statistical properties. Vortex core dynamics was investigated using the criterion of minimum total velocity. The turbulent swirl decay law was proved based on the integral flow characteristics, such as swirl parameter and average circulation. These results will help in constituting more reliable theoretical and numerical models for the turbulent swirl flow.

This investigation is an fundamental study about the perfomance of dynamic operated solid/mechanical vane vortex generators (VVGs). Fluidic vortex generators or so called vortex generator jets (VGJs) are more efficient in dynamic operation. Thus, the scope is to explore if VVGs are superior in dynamic operation, too. Besides, the influence of higher frequencies will be observed. The motion of the VVGs is generated by piezoceramic actuators or so called Marco Fiber Composites (MFC).The MFC actuators consist of bimoporh carbon fibre bars with applied piezoceramic face actuators on the top and downside. These MFC actuators generate a sinusoidal motion of the VVGs and were designed by analytical and experimental investigations. The MFC actuators are operated in resonance to gain the required displacement. Mass clamps applied on the bar tune the eigenfrequency into the operating point. Both, VVGs and MFC actuators, will bei integrated into a flat plate in a low speed wind tunnel. The VVGs penetrate through small plastic slits into a turbulent boundary layer. A stereo PIV system will record phase locked flow field pictures. The transient formation of the position and circulation of the vortex centers states that dynamic operated VVGs are supiror to static VVGs.