What is Supercavitation?

Super cavitation, also known as supercavitation, is an extreme form of cavitation. When supercavitation occurs, the entire near-wall region around the fluid is a mixed flow of vapor and liquid. When the pressure is low enough, a "cavity" filled with a vapor phase is formed, called a supercavity. Under the condition that the relative movement speed between the object and the liquid does not reach a sufficiently low pressure, the gas can also be manually injected to form a "ventilated supercavity" that mainly contains gas inside and covers most or all surfaces of the object.

Super-cavitation, also known as "supercavitation". Cavitation when the length of the cavitation region exceeds the range around the fluid. It is formed by the further reduction of the pressure in the low-pressure zone of the water flow and the continuous development of the cavitation zone. After the formation of supercavitation in the water flow, the flow resistance will increase. The cavitation collapse region of the supercavitation is far away from the structure, and the structure itself does not undergo cavitation erosion. Utilizing this characteristic in engineering, some structures are designed to be super-cavitated as a measure to reduce or exempt cavitation. ^[2]

Figure 4

The airfoil of a supercavitated hydromechanical runner blade is different from the common aerodynamic airfoil in terms of shape and dynamic characteristics.

FIG. 4 is a pressure distribution diagram of a common airfoil and a certain supercavitation airfoil. The common aerodynamic airfoil is a streamlined airfoil with a thicker front half and a thinner tail. The lift generated by the airfoil around the airfoil is mainly achieved by reducing the back pressure of the airfoil. The maximum thickness of a supercavitation airfoil is close to the tail of the airfoil, while the front half of the airfoil is thin. The lift of the airfoil around the airfoil is mainly formed by the frontal pressure of the airfoil. When the operating conditions change, the pressure change on the back of the airfoil is small. The positive side always maintains positive pressure.

The length of the cavitation cavities when the supercavitation airfoil flows around the supercavity chemical conditions (Figure 5)

Same-wing chord length

Ratio

Should be greater than 3 to 4, at least not less than 1.5, otherwise the unstable working conditions of the cavities will interfere with the flow around the airfoil surface.

Figure 5

There are many types of supercavitation airfoils. Foreign countries have developed various supercavitation airfoils with good performance for hydraulic machinery such as propellers and water pumps. Tests show that although the highest efficiency of a super-cavitation pump is lower than that of a general water pump, the performance of the super-cavitation pump is much better than that of a general water pump under the condition of air chemical industry, that is, the super-cavitation pump is no longer limited by cavitation. Can maintain high operating efficiency. ^[4]