Incipient cavitation in liquids flowing in pipes curved in one plane are affected by the pipe bend radii and pipe diameters, but little by pipe bend angles ranging from 60 to 120 degrees. Critical cavitation indices decrease with higher Reynolds number and pressure ratio. Bulk liquid temperature increase lowers the mean critical velocity at which cavitation occurs

Stonemetz, R. E.

English

NASA Technical Reports Server

May 1966	 Brief 66-10228 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Studies Reveal Effects of Pipe Bends on Fluid Flow Cavitation 
The problem: 
To determine the conditions that cause incipient 
cavitation in liquids flowing in pipes curved in one 
plane. Pipelines containing suction ducts and small 
bend radii are conducive to cavitation at high volu-
metric flow rates. Although considerable data are 
available on cavitation occurring in fluid flow over 
bodies of various shapes, little has been published on 
cavitation in pipe bends. Cavitation can cause erosive 
action in the bend areas and a loss in flow efficiency. 
The solution: 
The results of a series of tests using water as the 
working fluid, in a Reynolds number range of 4 x 10 
to 2 x 106 and at pressure ratios of 0.04 to 0.40, in 
pipe bends curved in one plane and made of a 
transparent plastic are as follows: 
1. Cavitation was affected by the pipe bend radii 
and the pipe diameters, and little, if any by pipe 
bend angles ranging from 60° to 120°. The 
critical cavitation index (i.e., the index computed 
for flow just entering cavitation) was greater for 
smaller ratios of bend radius to pipe diameter. 
2. Critical cavitation indices decreased with increas-
ing Reynolds number and pressure ratio (i.e., the 
ratio of liquid vapor pressure to upstream dynamic 
pressure). 
3. Increasing the bulk liquid temperature lowered 
the mean critical velocity at which cavitation 
occurred. 
4. An empirical relationship, taking into account 
the effects of bend radius and pipe diameter, was 
derived for the determination of the critical cavita-
tion index. 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
How it's done: 
Transparent pipe elbows having bends of 60°, 90°, 
and 120° in one plane, pipe diameters of 1.5, 2.0, 
and 4.0 inches, and bend-radius-to-pipe-diameter 
ratios of 0.7, 1.0, and 1.5 were subjected to varying 
water flow rates from a raised, open-top reservoir. 
The flow rate was regulated by replaceable orifices 
near the bottom of the downcomer below the test 
section. A three-probe pressure pickup arrangement 
was used to measure the average upstream static 
pressure. Single pressure measurements, directly op-
posite one another, were made in the bend. All 
pressures were recorded electrically. 
For computing the volume flow rate, the water 
reservoir was filled to a predetermined level and 
timed through a measured fall of such magnitude 
that steady flow conditions could be assumed to be 
established in 5 seconds and that the pressure-head 
differential would be negligible. With a given orifice 
size, test elbow, and reservoir liquid level, a shutoff 
valve was opened and a test was run. The orifice 
size was increased until cavitation was visually ob-
served in the elbow. For each run, maximum, 
minimum, and mean values were determined for the 
pressure at each probe position. The water tempera-
ture was varied from 70° to 130° F in steps of 
approximately 15° F. 
Notes: 
1. No consideration was given to the effects of 
dissolved gas, surface tension, rate of bubble 
growth by diffusion, surface roughness, and water 
cleanliness.
(continued overleal) 
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000227 2020-03-11T17:32:31+00:00Z
2. Inquiries concerning this innovation may be di-
rected to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama, 35812 
Reference: B66-10228 
Patent status: 
No patent action is contemplated by NASA. 
Source: R. E. Stonemetz 
(M-FS-516) 
Brief 66-10228	 Category 05


Studies reveal effects of pipe bends on fluid flow cavitation

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