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In this article, the performance of the novel external stimulation oscillator and the optimized self- excited oscillator has been investigated by CFD numerical simulation. The efficiency and stimulation mechanism of the two kinds of oscillators were analyzed in numeric form. The cycle proportion of wall-attached jet switching time was calculated separately at different operating frequency. Additionally the reason for the difference of two oscillators was analyzed and explained.

Fluidic oscillator as a fluid control device has been developed recent years. The oscillation jet of compressible fluid has been used in microfluidic mixer [

Using the Coanda effect [

Based on the previous research about the oscillator, the sonic oscillator was optimized to obtain a higher total pressure of outlet. Then the oscillator performance and stimulation characteristic were compared with the novel external stimulation oscillator.

Many two-dimensional and three-dimensional simulations suggest that the difference of node parameters is within 2%. Two-dimensional simulation can save a lot of time.

The FVM (Finite Volume Method) was used to discretize the governing equations, the Roe flux difference splitting scheme was adopted for the convection term and the central difference scheme for dissipation term. Second order implicit time step was chosen for unsteady integrals [

The total pressure of the nozzle inlet was P_{i} = 0.36 MPa, channel outlet P_{o} = 0.18 MPa, and the expansion ratio ε = P_{i}/P_{o} = 2. The peak value of the total pressure of stimulating flow was 0.36 MPa, and the valley value was 0.18 MPa. The waveform of the stimulating flow was trapezoidal wave by programming the incentive function (UDF). Two oscillators used the same nozzle width: W = 2.5 mm, and the same angle of splitter: θ = 20˚. Other structure parameters were showed in

K, the ratio of the total pressure of channel outlet to total pressure of nozzle inlet, denotes the total pressure retention rate. The higher total pressure retention rate of the oscillation jet means the less the energy loss. The K of the general and the optimized oscillators are shown in

Structure parameter | S (mm) | L (mm) | h (mm) | b (mm) | D (mm) | H (mm) |
---|---|---|---|---|---|---|

Sonic oscillator | 1.5 | 1.5 | - | - | 4 | 11 |

External stimulation oscillator | 1 | 3 | 2.25 | 0.5 | - | 10 |

Efficiency Parameter | Category of Oscillators | |||
---|---|---|---|---|

General Sonic Self-excited | Optimized Sonic Self-excited | General External Stimulation | Optimized External Stimulation | |

K | 70.4% | 82.2% | 82.6% | 89.4% |

On the contrary in external stimulation oscillator, the static pressure of stimulating inlet is higher than that of the downstream. The stimulating flow could be accelerated by self-expansion. So it scarcely consumed the energy of main jet. Therefore, the total pressure loss was much less than the self-excited oscillator as shown in

As

R, the ratio of the suspension time of main jet to the cycle time, denotes the cycle proportion of wall-attached jet switching time. The wall-attached main jet switching process is under the boost and momentum of the stimulating flow. Evaluation of the pros and cons of the switching process depends on the adherence behavior of main jet and the duration of swing. An increase in switching time keeps the oscillator in bi-pass state, which means turbulence and increased loss. Therefore, the smaller the R is, the less the energy loss is.

In order to change the oscillation frequency of sonic oscillator, the length of controlling tube was adjusted (

Due to the difference of stimulating characteristics, the efficiency of external stimulation oscillator is higher than that of distributary self-excited oscillator by nearly 10%, and the energy loss rate is reduced by almost 50% relatively.

The stimulating flow of distributary self-excited oscillator has no explosive and sustained characteristic. It must rely on the entrainment of the main jet to re-accelerate. So this process loses a large amount of kinetic energy. Unlike self-excited oscillation, stimulating flow of external oscillation drains from the same gas source with main jet. It makes the stimulating flow have the approximate total pressure with main jet. So a self-expan- sion influx with main jet would not consume too much energy.

L_{c} (m) | 1 | 1.3 | 1.5 | 2 | 2.3 | 2.5 | 3 | 3.5 | 4 |
---|---|---|---|---|---|---|---|---|---|

f (Hz) | 100 | 85 | 72 | 56 | 50 | 46 | 39 | 35 | 30 |

The jet switching speed is relatively slow in the distributary self-excited oscillator. At different oscillation frequencies, the cycle proportion of wall-attached jet switching time of self-excited oscillator are all higher than that of external stimulation oscillator.

The results from numerical simulation and analysis indicate that the novel external stimulation oscillator has the higher efficiency and the better stimulation performance.

This work was financially supported by the National Natural Science Foundation of China (51276026).

Junlong Li,Jiupeng Zou, (2016) Numerical Analysis on the Oscillator of External Stimulation and Self-Excited. Journal of Applied Mathematics and Physics,04,1494-1498. doi: 10.4236/jamp.2016.48156