Session: 01-01-04 Fluid Machinery Symposium

Paper Number: 131002

131002 - Optimization of a Closed 2-Channel Impeller With Experimental and Optical Support 

Due to the high number of solids in wastewater and the resulting increased susceptibility to clogging for wastewater pumps, wastewater impellers are classically designed with a low number of blades as semi-open or closed impellers. In addition to higher possible efficiencies, the closed impellers also have an advantage in terms of resistance to wear compared to semi-open impellers. However, the closed 2-channel impellers have not yet been able to demonstrate good resistance to clogging by fibrous materials. At the Chair of Fluid System Dynamics at the Technical University of Berlin, a prototype is being used in a clogging test rig, that can accommodate various geometries manufactured via 3D printers. This allows the testing and optimization of different blade and hub geometries to achieve a low susceptibility to clogging for this impeller type. A basic impeller for optimization has already been presented at AJK23 to introduce the methodology of the possible optimization. The methodology consists of the use of 3D CFD, the long-time functional performance test on the clogging test rig, and an optical access located at the suction side of the pump for the detailed investigation of the interaction between impeller and duster. Modification 0, which has already been demonstrated, showed poor clogging behavior concerning dusters and will be improved in this publication using the optimization strategy already presented.

Based on the findings of the basic impeller and the clogging behavior, another impeller, called modification 1, is designed and simulated, which is then manufactured and installed in the test rig. Based on the findings of modification 0, this impeller has a significantly thicker leading edge with almost the same blade length. This thickened blade leading edge is intended to allow the dusters to slip off, as the leading edge of modification 0 was the main reason for the increasing clogging. The clogging tests again show a noticeable clogging potential, but with a significantly lower degree of saturation, which describes the maximum amount of dusters that can be collected inside the impeller. This leads to a significantly improved degree of long-time functional performance. The optical method shows that the suction side of the blade instead of the blade’s leading edge in particular contributes significantly to clogging, which is why a further modification, called modification 2, is designed, simulated and tested which has a convex suction side of the blade. This convex suction side is intended to enable a slipping off the dusters. The results of modification 2 in the test rig show greatly improved clogging behavior with a significantly increased degree of long-time functional performance. Likewise, no dusters remained in the impeller after the end of the tests at the Best Efficiency Point, which indicates good slipping behavior. This is additionally illustrated in the optical tests. As an outlook, a revision of the hub geometry is given, since the 3D CFD simulation as well as the optical measurements of modification 2 have shown that the dwell time of the dusters in the impeller is still very long, as already shown in the previous publication regarding modification 0.

Presenting Author: David Beck Technische Universität Berlin