Shroudless VCT Impeller Geometry for Monotonic Head-Flow Curves
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Solution Overview
Problem
High specific speed VCT pumps exhibit unstable head characteristics at low volumetric flow rates due to a 'dip' in the head vs. flowrate curve, limiting their operating range and requiring complex casing treatments or nozzles that decrease efficiency.
Innovation Solution
A shroudless VCT pump impeller design with S-shaped shroud and mean streamline blade angles, minimizing discharge recirculation on the shroud sides, ensuring a monotonically decreasing head with increasing flow rates without grooves or double inlet nozzles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional VCT pump impeller design is used, then the pump can operate at high specific speed, but the head vs. flowrate curve exhibits a dip at low flow rates limiting the operating range
Solution Approach 1:
The patent applies local quality by creating S-shaped streamlines with inflection points at specific locations on the blade surfaces. The blade angle distribution is optimized locally along the streamline, with different curvature characteristics at different positions (leading edge, inflection point, trailing edge). This localized geometric modification eliminates discharge recirculation at low flow rates while maintaining efficient flow patterns at design flow rates, thereby resolving the head curve dip issue.
Solution Approach 2:
The patent employs curvature principles by designing S-shaped streamlines with specific inflection points. The streamlines transition from convex to concave curvature at the inflection point, creating a geometric configuration that redirects flow away from the discharge recirculation zone. This curvature-based design modifies the flow separation characteristics and eliminates the dip in the head vs. flowrate curve.
2Adaptability or versatility
If casing treatments like grooves or double inlet nozzles are added to eliminate head curve dip, then the operating range is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the solution from the casing and relocates it to the impeller blade geometry itself. Instead of adding grooves to the casing or using double inlet nozzles, the invention modifies the impeller blade streamlines to inherently eliminate discharge recirculation. This extraction of the functional requirement from auxiliary components and integration into the primary impeller design simplifies the overall system while achieving the same performance improvement.
Solution Approach 2:
The impeller blade design with S-shaped streamlines performs the function of eliminating discharge recirculation inherently, without requiring external casing treatments. The optimized blade geometry self-regulates the flow patterns across different operating conditions, providing the head curve dip elimination feature as an intrinsic property of the impeller rather than requiring additional complex components.
3Ease of manufacture
If conventional impeller blade geometry is used, then the manufacturing process is simple, but discharge recirculation occurs at low flow rates causing head instability
Solution Approach 1:
The patent applies parameter changes by modifying the blade angle distribution and streamline curvature parameters along the blade surface. The S-shaped streamlines are defined by specific geometric parameters (inflection point location, curvature radius, blade angle variations) that are optimized to eliminate discharge recirculation. These parameter modifications are implemented through standard impeller manufacturing processes, maintaining ease of manufacture while achieving head stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances the operating range of VCT pumps to beyond the best efficiency point (BEP) flow rate, maintaining efficiency and reducing complexity and cost.
Implementation Method 1
a motor 100 that drives a vertical shaft 102 which descends within a pit 104 into a pump casing 108 and rotates an impeller 106 inside the pump casing 108, which draws a liquid 110 up from the pit and out through a pump outlet 112
Implementation Method 2
Each of the blades has a pressure side 150 and a suction side 152
Data Source
AI summary
A shroudless vertical turbine pump (VTC) impeller and method of design thereof minimizes or eliminates discharge recirculation on the shroud sides of the impeller blades, thereby providing a monotonically decreasing head as a function of flow rate from zero flow to a flow rate that is beyond a best efficiency point (BEP) flow rate, and in embodiments beyond 120% of the BEP. Each blade of the impeller has S-shaped mean and shroud streamlines having inflection points located between the exit gate and the terminating edge. The disclosed method comprises varying locations of the inflections points for candidate designs and applying computational fluid dynamics (CFD) to determine successful candidates that meet all application requirements while providing a monotonic head/flow curve. In embodiments, this process is continued until an optimal impeller design is identified, for example a design that optimizes power, energy efficiency, and/or NPSHR.