Flat Versus Radius Parshall Flume Wing Walls

In 1994, Dr. Fred Blaisdell published an evaluation of the data collected by Dr. Parshall on his namesake flume. As part of the evaluation, Dr. Blaisdell tested both full size and scaled Parshall flumes to validate the ratings of 6-foot, 10-foot, and 15-foot flumes.

Blaisdell found that, at high flow rates, a wave and trough phenomena developed when standard 45º wing walls were used. As the flow rates increased, the phenomena, which started at the junction of the inlet wing wall and the entrance of the flume, increased and moved from the entrance of the flume towards the point of measurement.

wave phenomena at junction of wing wall and Parshall flume

As a result of his investigations, Blaisdell recommended the use of radius inlet wing walls in lieu of the more traditional 45º ones. The radius wing walls allowed for the formation of streamlines that were parallel to the flume sidewalls – which lead to less surface turbulence and more accurate flow measurement. This recommendation is in line with Dr. Parshall's later publications on the flume (1950, 1953), where only radius wing walls are shown (instead of his earlier works where 45º wing walls were depicted).

smooth flow into a Parshall flume using radius inlet wing walls

While 45º wing walls were found to introduce turbulence at higher flow rates, in applications where radius wing walls are not practical, it is still recommended that wing walls be used - instead of abruptly transitioning from a wider channel into the enterance of the flume.

Parshall flume with flat inlet wing walls