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

1995年设计并建造了一个新的泄放式空蚀风洞，用液氮研究了空蚀的热力学效应。1995年和1996年对文氏管中的汽蚀现象进行了研究，观察到了几度的温降，这与Z因子法的预测是一致的。1996年，在二维凸形断面上建造了一个矩形试验段，通过在试验段下游插入网格，在试验回路中产生有意的压降，改变试验段的空化数。本研究的主要目的是探讨这种泄放式风洞的可能性和可行性。在研究过程中，验证了该隧道的可行性。指出了需要改进的问题，即在试运前应将试验回路（包括试验段）充满试验液，以保证试验段处于热平衡状态，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等。试验环的热应力和收缩是另一个重要问题。

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.