Rain Bird Golf Division, Azusa, California

Engineers at Rain Bird’s Golf Division used CFD computer simulations to reduce the pressure loss in golf course irrigation components by more than 50 percent. Swing joints are the components that connect the sprinkler to the waterline in an irrigation system. Because they can dramatically reduce the cost of maintenance and replacement parts, swing joints are used in most golf courses to protect every sprinkler head. The only disadvantage of the traditional swing joint is the fact that the three 90° bends found in each one introduce a significant pressure loss. This pressure loss shows up as additional power required to run the central pumping stations found at almost every American golf course.

Contours of velocity magnitude are shown for one of the initial designs studied. CFD analysis showed that pressure loss and turbulence in the elbow was clearly concentrated in the inside corner region.	Contours of velocity magnitude are shown for the improved design

Rain Bird engineers recently initiated a project with the goal of substantially reducing these losses. They began by simulating the company’s and competitors’ existing elbow designs. The simulation results showed that pressure loss and turbulence in the elbow was clearly concentrated in the inside corner region. Existing designs at this time all had a sharp inside corner in order to minimize molding expense. But the analysis results showed that after passing this corner, water was directed immediately to the opposite outside wall of the elbow where it created a high-pressure zone. In effect, water was flowing only in the outside half of the pipe, reducing its effective diameter by 50 percent and greatly increasing pressure loss.

Developing an Improved Design

With just a few iterations of analysis, Rain Bird engineers gained a clear understanding of the problem and were well on their way to solving it. They quickly iterated toward a significant design change that had a major impact on pressure losses. First, the cross-sectional area of each elbow was increased by reducing the corner radius of the outer wall. Second, the sharp inside corner of the elbow was softened by increasing its corner radius. These changes reduced pressure loss by over 50 percent, by doubling the effective diameter of the elbow without changing its external dimensions.

Pressure loss chart

Analysis of the new design showed that the water flow now followed the larger diameter internal wall around the corner rather than rushing to the opposite wall. The result is that installing the new swing joint throughout a golf course can substantially reduce the amount of power required to drive the central pumping system. Another alternative, for golf courses that are satisfied with their existing power consumption, is to use smaller and less expensive swing joints without increasing pressure drop. For example, a Rain Bird Eagle 900 rotor, which normally requires a 1-1/2 inch swing joint, can now be supplied by a Rain Bird 1-1/4 inch diameter swing joint. The price of the 1-1/4 inch swing joint is about $8.00 less than the 1-1/2 inch swing joint. The savings on a large golf course would be on the order of $16,000.

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