Abstract: The numerical method for the simulations of the flow fields and thrusts of synthetic jet underwater were studied herein. The effects of grid resolution, the first height of the boundary layer and the turbulence model on the thrusts of synthetic jet underwater were debated in detail. It is found that the thrusts are not sensitive to the grid resolution and the turbulence model. The numerical results of the thrusts are well consistent with the experimental data, indicating the effectiveness of the numerical method in the simulations of synthetic jet underwater. The efficiency of the actuator under different L/D conditions are numerically studied. The results show that the efficiency is the highest when L/D is near 4. When L/D deviates from 4, the efficiency decreases. A mathematical model of the thrusts of synthetic jet underwater was established. And a nozzle deflectable synthetic jet actuator was designed. The thrust enhancement characteristics of synthetic jets were interpreted using this model through the comparison among the thrusts of the nozzle deflectable actuator under the deflection angle of 0 and 90 degree.

Key words: synthetic jet underwater, numerical method, thrust model, thrust enhancement mechanism

摘要： 研究了水下合成射流的数值计算方法，对比了不同网格尺度、不同边界层尺度以及不同湍流模型对合成射流流场以及推力的影响，结果发现，推力计算结果对网格尺度、边界层尺度及湍流模型并不敏感。将推力数值计算结果与已有的试验结果进行了对比，两者具有很好的一致性，验证了数值计算方法的正确性。研究了不同L/D（L为活塞直径，D为出口直径）条件下合成射流激励器的推进效率，结果显示，当L/D值在4附近时，合成射流推进效率最高；当L/D值偏离4时，推进效率降低，这与已有的试验结论一致，进一步证实了数值方法的正确性。建立了水下合成射流的推力模型，该模型将合成射流的推力分为以下3个部分：质量变化引起的动量变化、加速度引起的动量变化以及外部流体的阻滞作用。结合该模型，对一种出口可偏转合成射流激励器不同偏角下的推力进行了对比分析，证明合成射流的高效率源自于外部流体的阻滞作用。

关键词: 水下合成射流, 数值方法, 推力模型, 增强机理