Flow Inside the Sidewall Gaps of Hydraulic Machines: A Review

Abstract

The paper critically reviews the current state of the art in flow inside sidewall gaps of hydraulic pumps and turbines. It describes the consequences of the presence of this type of flow in turbomachinery and then relates it to other physical phenomena that determine the behavior, operating characteristics, and overall performance of the machine. Despite the small dimensions of the rotor-stator spaces, the flow in these regions can significantly affect the overall flow field and, consequently, efficiency. The circulation of the fluid inside the gaps and secondary flow that is caused by rotating elements influences the disk friction losses, which is of great importance, especially in the case of low specific speed pumps and turbines. The flow pattern affects the pressure distribution inside a machine and, thus, generates axial thrust. The presence of secondary flow also significantly changes the rotordynamics and can bring about undesirable vibrations and acoustics issues. This article aims to review and summarize the studies that were conducted on the mentioned phenomena. Experimental and numerical studies are both taken into consideration. It proposes some requirements for prospective research in order to fill current gaps in the literature and reveals the upcoming challenges in the design of hydraulic machines.

Effect of Splitter Blades on Performances of a Very Low Specific Speed Pump

“…At low specific speed, pumps provide high pressure at low flow rate. To achieve these performances, impellers have large diameters, causing an important part of the shaft power to be dissipated in the sidewall gaps of the pump due to disk friction [1,2]. These pumps are also prone to low-flow head instability, where a positive head slope at low-flow can be observed (dH/dQ > 0).…”

Fatigue Strength Analysis of a Prototype Francis Turbine in a Multilevel Lifetime Assessment Procedure Part II: Method Application and Numerical Investigation

“…Additional time dependence of the formula increases the complexity of the investigated correlation. A good review about the internal flow, arising unsteady flow phenomena and impact on runners axial thrust forces is shown in [46]. Within the framework of the research project MDREST, prototype site measurements for validation purposes were performed.…”

Influence of impeller blade rounding and surface roughness on the internal hydraulics and performance of pump as turbine

“…These water impurities adversely affect the performance of PAT due to an increase in surface roughness (ε). Therefore, 'ε' is one of the critical parameters influencing PAT performance, which needs to be studied in detail [17][18]. Further, it is noticed that the studies This article has been accepted for publication in a future issue of AME, but has not been fully edited.…”