Method for optimizing blade axis position of water pump under all operating conditions

A method for making an axial-flow pump blade with an optimal blade axis position and the smallest blade hydraulic torque under all operating conditions, characterized by comprising the following operation steps:

• A. determination of calculation conditions within a range of all the operating conditions of an axial-flow pump as follows:
• an operating head range of the axial-flow pump, m equally spaced heads are selected, m=5˜10, a minimum operating head Hmin and a maximum operating head Hmax are included, the head interval is
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• H
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• H
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• n
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• for each of the m heads, n blade angles are selected at certain intervals within the operating blade angle range of the axial-flow pump, n=5˜10, a minimum operating blade angle αmin and a maximum operating blade angle αmax are included, and determining m×n calculation conditions;
• B. three-dimensional modeling and mesh generation of a calculation area of a flow field of the axial-flow pump includes a straight section with a length about 1 time an impeller diameter in front of an impeller inlet, an impeller section, a guide vane body section, and a straight section with a length of 1˜2 times the impeller diameter behind a guide vane body outlet, and three-dimensional modeling and mesh generation are conducted on the calculation area of the flow field of the axial-flow pump at total n impeller blade angles;
• C. numerical simulation of the flow field of the axial-flow pump and calculation and determination of blade hydraulic torque as follows:
• a water-mass continuity equation, a momentum equation and k-B turbulence models are adopted, pressure inlet boundary conditions and mass flow outlet boundary conditions are adopted in the calculation area of the flow field of the axial-flow pump, and CFX fluid calculation software is used for numerical simulation of the calculation area of the flow field of the axial-flow pump under the m×n calculation conditions, so as to obtain the blade hydraulic torques at different heads and different blade angles, which are listed in a table;
• D. determination of a range of a position of a blade resultant hydraulic pressure action line of the axial-flow pump and the optimal blade axis position under all the operating conditions as follows:
• according to the blade hydraulic torque and the resultant hydraulic pressure of the axial-flow pump under m×n calculation conditions calculated in steps A-C, the distance between the blade resultant hydraulic pressure action line and the current blade axis approximately on a calculation cylindrical surface under the m×n calculation conditions of the axial-flow pump is
• L
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• M
• F
• w
• ,
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• wherein L—the distance from the blade resultant hydraulic pressure action line to the current blade axis;
• M—the blade hydraulic torque;
• FW—the blade resultant hydraulic pressure, and then the optimal blade axis position is located between two blade resultant hydraulic pressure action lines farthest from each other in all the operating conditions;
• E. determination of a small region of the optimal blade axis position of the axial-flow pump under all the operating conditions includes a range width between the two blade resultant hydraulic pressure action lines farthest from each other approximately on a calculation cylindrical surface is s, the range width s is divided into k equal parts, starting from the action line closer to the current blade axis, in the two blade resultant hydraulic pressure action lines farthest from each other, blade axes 1, 2, . . . , k−1, k are set at the equal parts to the other end of the range with the width s, and distances between the k blade axes and the starting resultant action line are set as slk, 2slk, (k−1)slk, s respectively;
• a coordinate system is established, an abscissa represents a distance from the set blade axis position to the current blade axis, and an ordinate represents a maximum hydraulic torque of a blade under all the operating conditions at different blade axis positions;
• the blade hydraulic torques of the axial-flow pump under m×n calculation conditions when the blade axis is located at the set k different blade axis positions are calculated, the blade hydraulic torque with the largest absolute value of the axial-flow pump under the m×n calculation conditions at each set blade axis position is determined, positions of two set adjacent blade axes O1-O1 and O2-O2 in which an algebraic value of the hydraulic torque with the largest absolute value is positively and negatively converted are found, and then the optimal blade axis position is located in the small region between the O1-O1 axis and the O2-O2 axis, further narrowing the range of the optimal blade axis position;
• F. determination of the optimal blade axis position of the axial-flow pump under all the operating conditions includes on a calculation cylindrical surface in the blade, for the small region between the two set adjacent blade axes O1-O1 and O2-O2 in which the maximum hydraulic torque of the blade of the axial-flow pump under all the operating conditions is positively and negatively converted, a 0.618 golden section method is conducted to accelerate the fine approximation to the optimal blade axis position so as to minimize the maximum hydraulic torque of the blade of the axial-flow pump under all the operating conditions;
• if the maximum hydraulic torque under all the operating conditions is positive for the blade axis O1-O1 and the maximum hydraulic torque under all the operating conditions is negative for the blade axis O2-O2, a blade axis O3-O3 is set at a distance of 0.618slk from the axis O1-O1 to the axis O2-O2, and the maximum hydraulic torque of the blade of the axial-flow pump under all the operating conditions for the blade axis O3-O3 is calculated and determined;
• if the maximum hydraulic torque of the blade of the axial-flow pump under all the operating conditions for the blade axis O3-O3 is positive, it is indicated that the optimal blade axis is located between the axis O3-O3 and the axis O2-O2, then a blade axis O4-O4 is set at a distance of 0.618×(1−0.618)slk from the axis O3-O3 to the axis O2-O2, and the maximum hydraulic torque of the blade of the axial-flow pump under all the operating conditions for the blade axis O4-O4 is calculated and determined;
• if the maximum hydraulic torque of the blade of the axial-flow pump under all the operating conditions for the blade axis O3-O3 is negative, a blade axis O4-O4 is set at a distance of 0.618×0.618slk from the axis O1-O1 to the axis O3-O3, and the maximum hydraulic torque of the blade of the axial-flow pump under all the operating conditions for the blade axis O4-O4 is calculated and determined;
• repeat these steps, continue this way until a distance Δs between the last approaching two adjacent blade axes is small enough to satisfy a formula (2),
• Δs≤0.001m (2)
• the blade axis at this position is the optimal blade axis, which can ensure the minimization of the maximum hydraulic torque of the blade of the axial-flow pump under all the operating conditions;
• G. comparison of blade hydraulic torques before and after optimization of the blade axis position of the axial-flow pump includes the blade hydraulic torque under each calculation condition after optimization of the blade axis position is calculated and listed in a blade hydraulic torque table after the optimization of the blade axis position;
• by taking a blade angle as an abscissa and the blade hydraulic torque as an ordinate, the blade hydraulic torques of the axial-flow pump under m×n calculation conditions before and after the optimization of the blade axis position are plotted on a graph, and blade hydraulic torque points at the same head but different angles are connected to compare the blade hydraulic torques before and after the optimization of the blade axis position;
• and results show that after the optimization of the blade axis position of the axial-flow pump, the maximum absolute hydraulic torque of the blade under all the operating conditions is reduced by 45%˜50%, and the average absolute hydraulic torque of the blade is reduced by 75%˜80%;
• and
• H. creating the axial-flow pump blade with the optimal blade axis position and the smallest blade hydraulic torque under all operating conditions according to step A to step H.