Masahiro Ishigaki

Measurements of acoustic streaming in a looped-tube thermoacoustic engine with a jet pump

This paper reports on the acoustic streaming in a looped-tube thermoacoustic prime mover equipped with an asymmetric constriction called a jet pump. The time-averaged mass flow velocity was determined using visualization methods and using acoustic field measurements. It was demonstrated that the magnitude and the direction of the velocity were dependent on the orientation of the jet pump. From the observed velocities, we estimated the heat carried away from the hot heat exchanger by the mass flow. It was shown that the heat loss was decreased from 30 W to 6.5 W by reversing the orientation of the jet pump, when the input heat power supplied to the prime mover was 100 W. The influence of the acoustic streaming was also studied from the cooling temperature of the looped-tube cooler.

Numerical analysis of thermoacoustic spontaneous oscillations in a 2D rectangular and an axisymmetric closed tube

We analyze stability of thermoacoustic spontaneous oscillations of helium gas (Taconis oscillations) using the numerical simulation. The flow fields in a 2D rectangular closed tube and a circular cylindrical closed tube are simulated by solving the 2D and axisymmetric compressible Navier-Stokes equations, respectively. In the 2D rectangular tube, two steady states (oscillation state and quiescent state) are obtained at the same temperature ratios. On the other hand, in the axisymmetric cylindrical tube three different oscillation modes are observed: the fundamental mode and the second mode of a standing wave, and the oscillation with a shock wave.

Stability of thermo-acoustic oscillation in a closed tube by numerical simulation

The thermo-acoustic oscillation (Taconis oscillation) in a two-dimensional (2D) closed tube with a large thermal gradient was studied by numerical simulation of the 2D compressible Navier–Stokes equations. Both ends of the tube were hot (T=TH), and the center of the side wall was cold (T=TC). We analyzed the stability of thermo-acoustic oscillations in the closed tube at various values of the initial pressure p0 and temperature ratio θ=TH/TC. Hysteresis phenomena were observed when the boundary layers are thin at the initial pressures 25, 35, 50, 75 and 100 kPa. On the other hand, we could not observe the hysteresis phenomenon when the boundary layer is thick at the initial pressure of 17.5 kPa. We analyzed the temperature distributions in the cold region, and a heat pumping from the cold region toward the hot region was observed in the cold region. These heat pumping phenomena are related to the hysteresis phenomena.

Visualization of Acoustic Streaming in a Looped Tube Thermoacoustic Engine with a Jet Pump

The steady flow induced in a looped tube thermoacoustic engine having a jet pump is visualized using a sheet‐like laser light and small tracer particles. It is shown that the acoustic streaming velocity and its direction depend on the configuration of the jet pump. The performance of the looped tube cooler is also shown to be significantly affected by the acoustic streaming induced in the loop.

Numerical Analysis of Stability of Thermo-acoustic Oscillation in a 2D Closed Tube

‡The thermo-acoustic oscillation (Taconis oscillation) in a two dimensional closed tube with large thermal gradient is studied by numerical simulation of the two-dimensional compressible Navier-Stokes equations. Both ends of the tube are hot (T = T H ), and the center of side wall is cold (T = T C ). We analyze the stability of thermo-acoustic oscillations in the closed tube with different initial pressures and temperature ratios θ = T H /T C . We observe two steady states between the temperature ratio 5.88 ≤ θ ≤ 6.49 at the initial pressure p 0 = 1 x 10 5 Pa. On the other hand, we do not observe the hysteresis phenomenon at the initial pressure p 0 = 0.175 x 10 5 Pa. We analyze the energy flow in the tube length direction, and the heat pumping is observed in the cold region.