Numerical simulation of particle motion in an ultrasound field using the lattice Boltzmann model.

In this paper we investigate the motion of small particles suspended in a fluid through which an ultrasound field is propagating. The application of the lattice Boltzmann model to this problem is considered using a two dimensional model. Particles in an ultrasound field are observed to move with a mean particle motion. Further, the time-averaged force on a fixed cylinder is computed and found to be in good agreement with a theoretical expression for the radiation force. Simulations are performed with a single particle, although the approach can equally be applied for a larger number of particles.

PIV applied to eckart streaming produced by a medical ultrasound transducer.

Particle image velocimetry (PIV) is applied for the first time to study Eckart streaming induced by a medical ultrasonic transducer operating at a frequency of 3.3 MHz and effective acoustic intensities of 0.25 and 3 Wcm(-2). A temporal series of velocities in a two-dimensional plane were recorded resulting in an experimental set comprising over half a million velocity data points. These enabled average and fluctuating properties to be determined and clearly indicated the quasi-steady nature of the flow. The average large scale velocity fluctuations along the axis caused by this quasi-steady property were calculated to be 2 and 20 m ms(-1) at effective intensities of 0.25 and 3 Wcm(-2) respectively corresponding to approximately 25% of the peak flow velocity in both cases. Furthermore averaged shear rates were calculated with peak values of 1 and 8 s(-1) for the low and high intensities respectively. The present investigation indicates the usefulness of PIV for such studies and serves as a prelude to investigations of streaming in biological type fluids.

Particle image velocimetry analysis using an optically addressed spatial light modulator: effects of nonlinear transfer function.

Optical processors for generating a two-dimensional squared autocorrelation function have been presented for postprocessing particle image velocimetry photographs of fluid flows. The incoherent-tocoherent conversion can be performed by an optically addressed spatial light modulator. The transfer function of these devices is far from linear and will influence the performance of the optical processor.

Two different transfer functions, characterizing the two main types of commercial optically addressed spatial light modulators as an analog and a binary transfer function, have been simulated digitally.

Results of numerical simulations on the influence of introducing these nonlinear transfer functions to the correlation function for particle image velocimetry analysis are presented.

Spectral analysis and cross-correlation techniques for photon counting measurements on fluid flows.

Photon counting techniques for the measurement of turbulent fluid flows are analyzed, and it is shown that considerable errors can result if conventional Fourier methods are used to transform count correlation records from LDV systems onto the frequency domain. Two alternative schemes are presented that overcome this difficulty. The first involves the use of high resolution spectral techniques to transform count autocorrelation records, and the second makes use of the count cross-correlation between signals from two detectors. A theoretical analysis is presented for the count cross-correlation process, and experiments in air flow show turbulence levels predicted by the two methods to be in close agreement.