Combined Particle Image Velocimetry Research Articles

An Experimental Study on Turbulent Circular Wall Jets

The results of a laboratory investigation on the characteristics of a circular three-dimensional turbulent wall jet are presented. Measurements were performed up to 50 nozzle diameters using a combined Particle Image Velocimetry and Planar Laser Induced Fluorescence approach that captured simultaneously the planar velocity and concentration fields. Both the velocity and concentration profiles exhibited similarity in the streamwise and spanwise directions after sufficient distance from the nozzle. The existence of a secondary mean motion is shown to be responsible for the far greater lateral spread compared to the normal spread for both the momentum and scalar mixing. Using curve fitting, the mean properties of the three-dimensional wall jet are approximated. The consistency of the relationships is further examined based on mass conservation and momentum balance.

Simultaneous two-dimensional flow velocity and gas temperature measurements by use of a combined particle image velocimetry and filtered Rayleigh scattering technique

For the first time, to the best of our knowledge, two-dimensional instantaneous measurements of the flow velocity and the gas temperature have been performed in a turbulent flame with simultaneous use of particle image velocimetry and planar filtered Rayleigh scattering. These single-shot measurements provide simultaneous information on the local flame structure (curvature and temperature gradients) and on the local flow conditions (vortices, flow divergences, and strain rates). The applicability of the technique is demonstrated in a turbulent lean CH(4)-air V flame.

Rocking motion, trajectory and shape of bubbles rising in small diameter pipes

The trajectory, rocking motion, and shape of a single air bubble rising in water were investigated utilizing the particle tracking velocimetry (PTV) measurement technique. The three components of the velocity and acceleration vectors of the bubble were obtained by employing a stereoscopic technique. This technique allowed for a better description of rising bubble behavior. Four charged coupled device (CCD) cameras at different view angles acquired the view volume images. Two experimental configurations were employed in this study. In the first setup the bubbles were tracked for a duration of 133.3 ms. The viewing area was 24.6 mm high and 18.6 mm wide, so the bubbles trajectories could be determined. In this configuration, the bubbles rose in a stagnant and a laminar water flow. The average equivalent spherical diameter of the bubbles was 3.6 mm. In the second experimental setup configuration, the bubbles were tracked for 66.7 ms, but the viewing area was reduced to 11.0 mm high and 13.0 mm wide. In addition, a combined shadow particle image velocimetry (SPIV) technique was employed. This technique allowed for an accurate description of the bubble shape. The results indicate that the trajectory of the bubbles was zigzag or helical, and the shape was oblate spheroidal. The period of the cyclic motion and the amplitude decreased as a result of the wall effect. The bubbles rising close to the pipe wall have more rotational behavior than the bubbles flowing through the pipe center. This is a consequence of bubble/wall interaction.

Probing the velocity fields of gas and liquid phase simultaneously in a two-phase flow

The feasibility of simultaneous measurements of the instantaneous velocity fields of gaseous and liquid phase is demonstrated in a laminar, unsteady two-phase flow. Thus, the instantaneous relative velocity field can be measured in such media. This is achieved by combining Particle Image Velocimetry (PIV) and a gas-phase velocimetry technique, which is based on laser-induced fluorescence (LIF) from a gaseous tracer. The wavelength shift of LIF is exploited to separate it from Mie scattering from the liquid phase. The new technique and the PIV measurement system work independently in this approach. Thus, the measurement accuracy and precision of the new technique can be validated by comparing it to the PIV results in regions of the flow field where the relative velocity vanishes.

Measurement of mixing processes with combined digital particle image velocimetry and planar laser induced fluorescence

Abstract A combined digital particle image velocimetry (DPIV) and planar laser induced fluorescence (PLIF) approach was developed to measure both the time mean and turbulent mass transport in mixing processes. The system couples the two well-known techniques to enable synchronized planar measurements of flow velocities and concentrations in a study area. The potential interference effect between the seeding particles for DPIV and the fluorescent dye excitation for PLIF was carefully investigated. The performance of the system was verified with the experimental results of a turbulent round jet discharging into a stagnant environment. Comparison between the measurements obtained in the present study with the large body of existing information on pure jets is satisfactory. The key advantage of the shorter duration required with this approach compared to point-based techniques is highlighted.

Combined particle image velocimetry and visualization experiments on instabilities in a flat plate boundary layer with zero pressure gradient

Quantitative and visual data of artificially forced instabilities are acquired in a flat plate boundary layer in air. For the first time, particle image velocimetry (PIV) allows the instantaneous recording of a complete velocity field. With this technique, quantitative data are obtained within the boundary layer and very close to the wall. By using a light sheet technique it is possible furthermore to obtain visual data. Reproducible and constant conditions in the development of the instabilities are achieved by forcing the boundary layer with well-controlled disturbances. These disturbances are generated with an arrangement for acoustic excitation.

Three-dimensional study of Rayleigh-Bénard convection by particle image velocimetry

A three-dimensional study of the flow velocity field can be obtained by combining particle image velocimetry measurements in several parallel fluid planes with appropriate numerical processing. This process has been used to investigate the Rayleigh-Bénard convective flow in a small box. The light source was a 5 mW He-Ne laser with an electromechanical chopper that produced pulses of 6 ms minimum duration and 100 ms separation. The data reduction by fringe analysis provides at least 200 in-plane velocity vectors in each of the 15 fluid planes that were studied. From them, the out-of-plane velocity component was calculated, which allowed a complete three-dimensional flow map to be constructed.

Stereoscopic particle image velocimetry

The three components of the velocity field in a plane can be measured simultaneously by combining particle image velocimetry (PIV) and stereoscopy. A set-up has been devised to take two stereoscopic images of the flow simultaneously with only one camera, thus making automatic recording of three-dimensional (3D) velocity fields quite straightforward. Theoretical and practical considerations in implementing this stereoscopic PIV system are presented. The performance of the technique has been investigated by measuring several known displacements produced on a solid surface, and the application of the system to the measurement of the 3D velocity field in an acoustic streaming flow is presented.

Time-resolved particle image velocimetry used in the investigation of cavitation bubble dynamics

The temporal evolution of the velocity field of an unsteady fluid flow can be tracked by combining particle image velocimetry and high speed photography. We used this technique to investigate the flow around cavitation bubbles during their collapse near a solid boundary. The light source was an argon laser with an external acoustooptic deflector which produces series of short pulses. Using a drum camera for high speed photography, we achieved a temporal resolution of 10 kHz and a spatial resolution of better than 2 points/ mm(2). Velocities could be determined without directional ambiguity in a range from 2 to 30 m/s.

Time resolved particle image velocimetry

The temporal evolution of the velocity field of an unsteady fluid flow can be tracked by combining Particle Image Velocimetry (PIV) and high speed photography. Two alternative techniques for PIV are discussed: the classical light sheet technique and a method which makes use of the light scattered in forward direction. We applied time resolved PIV to investigate the flow around cavitation bubbles during their collapse near a solid boundary. The light source was an argon laser with an external acousto-optic deflector which produces series of short pulses. Using a drum camera for high speed photography, we achieved a temporal resolution of 10 kHz and a spatial resolution of better than 2 points/mm 2. Velocities could be determined without directional ambiguity in a range from 2 m/s to 30 m/s.