_Article_  
Study into the Improvement of Dynamic Stress Characteristics and Prototype Test of an Impeller  
Blade of an Axial-Flow Pump Based on Bidirectional  
Fluid-Structure Interaction  
[PERSON] 1, [PERSON] 1,*, [PERSON] 2,*(), [PERSON] 3, [PERSON] 4 and [PERSON] 1  
College of Energy and Electrical Engineering, Hohai University, Nanjing 211100, China  
College of Agricultural Engineering, Hohai University, Nanjing 210098, China  
School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China  
College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China  
Correspondence: [EMAIL_ADDRESS] (Y.Z.); [EMAIL_ADDRESS] (H.C.); Tel.: +86-25-83786979 (Y.Z.); +86-15195977674 (H.C.)  
Received: 20 July 2019; Accepted: 29 August 2019; Published: 2 September 2019  
**Featured Application: The thickness of rotating parts of hydraulic machineries, such as the impeller blade of axial pump studied in this paper, affect the hydraulic performance as known. However, unsuitable thin thickness will cause cracks on the structure. This paper design and validate an approach of thickening impeller blade root to increase the strength of blade and minimize the impact on hydraulic performance. An experimental method for the underwater measurement of the dynamic stress of prototypical hydraulic machinery was put forward to validate the simulation results. This study can be referred to enhance stability at design stage for structure of hydraulic machineries' blades.**  
This paper performed a numerical study into the dynamic stress improvement of an axial-flow pump and validated the simulation results with a prototype test. To further analyze the dynamic stress characteristics of impeller blades of axial-flow pumps, a bidirectional fluid-structure interaction (FSI) was applied to numerical simulations of the unsteady three-dimensional (3-D) flow field of the whole flow system of an axial-flow pump, and the gravity effect was also taken into account. In addition, real-structure-based single-blade finite element model was established. By using the finite element method, a calculation of the blade's dynamic characteristics was conducted, and its dynamic stress distribution was determined based on the fourth strength theory. The numerical results were consistent with the prototype tests. In a rotation cycle, the dynamic stress of the blade showed a tendency of first increasing, and then decreasing, where the maximum value appeared in the third quadrant and the minimum appeared in the first quadrant in view of the gravity effect. A method for reducing the stress concentration near the root of impeller blades was presented, which would effectively alleviate the possibility of cracking in the unreliable region of blades. Simultaneously, an experimental method for the underwater measurement of the dynamic stress of prototypical hydraulic machinery was put forward, which could realize the underwater sealing of data acquisition instruments on rotating machinery and the offline collection of measured data, finally effectively measuring the stress of underwater moving objects.  
pump impeller blades; fluid-structure interaction; gravity effect; stress characteristics improvement; prototype test