| The vehicle fire centrifugal pump is the key equipment for fire-fighting and rescue of the fire rescue brigade,and its function is to provide the fire-water with constant flow and high head for fire-fighting and cooling protection at the scene of the fire.When the vehicle fire centrifugal pump is in use,its inlet cross-section presents non-uniform flow state due to the layout of fire hose or the restriction of installation space.The non-uniform inlet flow can cause the degradations of hydraulic efficiency and cavitation performance of vehicle fire centrifugal pump to result in the reduction of outlet water pressure,and then affect the fire-fighting efficiency and fighting capability of the fire rescue brigade.At present,few basic theoretical studies on inner flow mechanism and optimization design of the vehicle fire centrifugal pump with non-uniform inlet flow are conducted,therefore,in order to study the inner flow mechanism of the vehicle fire centrifugal pump and establish the optimization design method to improve the operation efficiency,this dissertation is based on the National Science and Technology Support Programme Project(2011BAK03B05)“Research on New Equipment and Application Technology for the Urban Fire Fighting”and the National Key Technology R&D Program Project(2016YFC0800608)“Key Equipment Technology of Water Supply and Smoke Exhaust in Large Fire Sites and Integrated Fire-fighting Individual Equipment”,to study the mechanism of the influence of non-uniform inlet flow on the performance and inner flow characteristics of centrifugal pump and to establish the optimization design method of the vehicle fire centrifugal pump by using the prototype pump with the flow rate of 25 m~3/h.Then the method is applied to optimize the design of CB10/90 vehicle fire centrifugal pump.The main research contents and innovations are as follows:1.The inner flow law of vehicle fire centrifugal pump performance degradation induced by non-uniform inlet flow is mastered.The performance characteristics,cavitation characteristics and inner flow structure of CB10/90 vehicle fire centrifugal pump with straight pipe and elbow are compared and studied by the method of test and numerical analysis.Under the rated flow condition,the efficiency of the vehicle fire centrifugal pump with elbow decreased by 8%,the pump head decreased by 7m,and the NPSHr increased by 0.77m.The inner flow variations of vehicle fire centrifugal pump caused by non-uniform inlet flow mainly concentrate on the front part of impeller channel.On the same radial cross-section of impeller,the area of low pressure zone of elbow pump is obviously larger than that of straight-pipe pump,and the decentered flow is observed.The pressure of blade suction surface of elbow pump is lower than that of straight-pipe pump,which causes the pressure difference between working surface and suction surface of blade to increase and induce the increase of periodic radial force on the impeller because of nonuniform force on each blade.However,with the development of the fluid in the impeller channel,the flow is gradually uniform,and the flow state at the volute is similar to that of the pump with uniform inflow.Meanwhile,the calculation results of flow losses of impeller and volute show that the hydraulic loss of impeller increases by more than 3 m due to non-uniform inflow,and the variation of hydraulic loss in volute is small.Inner flow variation and loss calculation show that the non-uniform inlet flow is mainly influence on the impeller channel.2.The inner flow characteristics of centrifugal pump with non-uniform inlet flow are obtained by the PIV test technique.The database of design parameters of the vehicle fire centrifugal pump with non-uniform inlet flow is established.The elbow radius ratio,blade inlet angle,blade number,blade wrap angle,blade outlet angle,impeller outlet diameter,blade outlet width and flow area ratio are taken as the basic parameters.With dimensionless treatment,the design parameters of the excellent hydraulic model can be used to optimize similar pumps of same specific speed and different sizes.Based on the prototype pump with the flow rate of 25 m~3/h,the performance test and PIV inflow test platform of centrifugal pump with non-uniform inlet flow are built,and the test control system and data acquisition system are established.The performance and inner flow characteristics of the centrifugal pump with elbow inflow are tested and studied.The elbow inflow causes the prototype pump head to drop by 10%,the efficiency to drop by 8%,and the NPSHr to increase by 0.8m.Under the operating conditions of 0.8Q_D、1.0Q_D及1.2Q_D,the flow velocity distributions at the impeller inlet of centrifugal pump with elbow are biased to some extent.The main body of the liquid flow is inclined to the outer wall of the elbow,and the fluid velocity near the inner wall is lower.Especially at the0.8Q_D condition,the non-uniform velocity distribution at the impeller inlet extends to the entire impeller passage with the fluid flow in the impeller.Each blade of impeller is subject to different loads,which results in the deflection of impeller in the radial direction to affect the operation stability of the drive shaft.3.The inner flow mechanism and the significant factors affecting the efficiency of the vehicle fire centrifugal pump are found.Based on the database of design parameters of the vehicle fire centrifugal pump,the design parameters of the centrifugal pump are analyzed by orthogonal test.A combination orthogonal table of 8factors and 3 levels is established,and 27 groups of scheme combinations are obtained.The performance characteristics of 27 schemes are predicted by numerical simulations,and the simulation method is verified by the performance test of prototype pump.In the orthogonal scheme,the maximum difference of head and efficiency are 8.7m and 11.2%respectively.By the range analysis,the primary and secondary relationships of eight factors are obtained.The blade inlet angle,impeller outlet diameter and area ratio have greater influence on pump efficiency.Especially,the level change of the blade inlet angle can cause a great variation of the impeller inlet flow field.The inner flow comparison of the impellers with four blades,five blades and six blades,shows that the proper increase of the blade inlet angle is beneficial to the improvement of non-uniform inflow.4.The optimization design method of the vehicle fire centrifugal pump based on the hybrid algorithm is established for the first time.The hybrid algorithm of genetic algorithm and particle swarm optimization is founded to design optimally the prototype pump with elbow,which combines the strong global search ability of genetic algorithm and the strong local search ability of particle swarm optimization.An optimization design method of vehicle fire centrifugal pump with non-uniform inlet flow based on the hybrid algorithm is established by optimizing the prototype pump with non-uniform inlet flow.The pump performance and inner flow characteristics of the prototype pumps before and after optimization are compared and analyzed by combining the numerical simulation with the experimental verification,which verifies the feasibility of this optimization design method.The CB10/90 vehicle fire centrifugal pump with elbow is optimized.The large-scale turbulence structure in the optimized impeller passage is improved,and the impeller inlet pressure is obviously increased.The appropriate increase of blade inlet angle is conducive to matching non-uniform inlet flow,reducing shock loss and improving pump efficiency.Under the rated flow condition,the efficiency of the optimized vehicle fire pump is increased by 4.1%,and the NPSHr is decreased by 0.38m.The pump performance is obviously improved.5.The generation and development law of radial hydraulic force of the centrifugal pump with non-uniform inlet flow are studied.Based on numerical analysis and empirical formula calculation,the radial force characteristics of the prototype pump with straight pipe and elbow are analyzed.The radial forces of the prototype pump under two kinds of water inlet flow conditions are periodic and the periodic shapes are similar,which shows that the unsymmetrical structure of volute is the main cause of radial hydraulic force on the prototype pump.The influence of non-uniform inlet flow on radial hydraulic force of prototype pump is quantified,the elbow flow causes the radial hydraulic force of prototype pump to increase by around4%.Comparing the radial force characteristics of prototype pumps before and after optimization,the improvement of nonuniform flow in impeller channel reduces the radial force of prototype pump by around 2%. |
