Development and Experiments of Cavitation Tunnel for the Liquid with Very Low Temperature

1995年1月，设计并施工了一种新型吹落式空化隧道，采用液氮对空化进行了热力学效应研究。1995年和1996年对文丘里的空化现象进行了研究，观测到温度下降了几度，与z因子法预测的结果一致。1996年，建立了矩形试验截面，对二维凸形进行了空化试验。通过在下游插入网格来改变测试段的空化数，从而在测试回路中产生有意的压降。本研究的主要目的是探讨这种比普通隧道更方便、更便宜的排空式隧道的可能性和可行性。在研究过程中，验证了隧道的可行性。并指出了有待改进的问题。在试运行前，包括测试段在内的测试回路应充满测试液，以保证测试段处于热平衡状态。其他需要解决的问题是温度计和压力表的准确校准方法，以及流量计在极低温度下的故障。热应力和收缩是测试回路的另一个重要问题。

A new blow-down type cavitation tunnel was designed and constructed in the first year, 1995 where the liquid nitrogen was used to investigate the thermodynamic effect on cavitation. In 1995 and 1996, cavitation in Venturi was investigated and observed the temperature drop of a few degrees which agreed with the prediction by Z-factor method. In 1996 a rectangular test section was constructed to test the cavitation on a two-dimensional convex shape.The cavitation number at the test section was changed by inserting meshes downstream to produce an intentional pressure drop in the test loop.The main purpose of the present research is to ihvestigate the possibility and the feasibility of such the blow-down type tunnel, which is much handy and cheaper than the normal type tunnnel.During the research the feasibility of the tunnel was verified. The problems to be improved were also pointed out.The test loop including the test section should be filled with the test liquid before the test run, so that the test section is insured in thermal equilibrium condition.Other problems to be solved were accurate calibration methods of thermometers and pressure gauges, and mal-eunction of the flow meter at very low temperature. The thermal stress and shrinkage of the test loop were other important problem.