Research On The Artesian Flow Characteristics Of Axial-flow Circulating Pump For Warships

The axial-flow circulating pump is one of the key hydraulic components in circulating water system of modern warships.When the navigational speed of warship meets certain requirement,the circulating pump will operate under artesian flow condition and its impeller rotates passively at low speed.The characteristics of unsteady internal flow and excitation of circulating pump under artesian flow condition are different from those under normal condition,which is very important for the integrated technical indicators of circulating pump and the stable operation of circulating water system.In this paper,the axial-flow circulating pump of low specific speed is studied.According to the experimental measurements and numerical calculations,the research on artesian flow performance,unsteady internal flow and excitation of the model pump under different operating conditions are carried out.The main research work and results are as follows:1.The DN200 closed loop test system is set up and then the performance parameters and pressure pulsation signals of the model pump under different artesian flow conditions are measured.The performance of the model pump under artesian flow condition is obtained and the uncertainties of measured values are analyzed.The validity of numerical simulation is verified from rotation speed and pressure pulsation under artesian flow condition.The research shows that the accuracy of parameters measured by this system meets the requirements of level one in GB/T 3216-2016.The rotation speed,flow loss and flow loss coefficient increases linearly,increases exponentially,decreases rapidly and then stabilizes with the artesian flow rate increases.When the flow rate is equal to the design value,the rotation speed of impeller under artesian flow condition is smaller than that under normal condition.2.The large eddy simulation method is adopted to simulate the unsteady flow in model pump under different artesian flow conditions.The BVF and limit streamline methods are used to analyze the characteristics of flow near blade surface.The characteristics of unsteady internal flow in model pump under different artesian flow conditions are discussed by analyzing the distribution of streamline and evolution of vortex.The research shows that the positive and negative peak areas of BVF on blade pressure surface increases with the artesian flow rate increases.The phenomenon of separation flow on blade pressure surface occurring at 1/5 chord from inlet edge which near the hub and backflow on both sides are typical flow characteristics under artesian flow condition.From hub to shroud,the extent of separation flow in impeller shows an enhancing trend,but the extent of separation flow and the scale of separation vortex in guide vane show weakening trends.The extent of separation flow in impeller has no obvious change with the artesian flow rate increases,but the extent of separation flow and the scale of separation vortex in guide vane show weakening trends with the artesian flow rate increases.The phenomenon of large-scale separation flow in guide vane and complicated wake flow is the main flow characteristic of pump under artesian flow condition.The trajectory slope of shroud leaking vortex decreases with the artesian flow rate increases,but the strength of vortex in guide vane channel increases with the artesian flow rate increases.The evolution period of separation vortex at the leading edge of guide vane is equal to 1/5 impeller rotation period.3.The results of experimental measurement and numerical calculation about pressure pulsation are processed and analyzed,and then the characteristics of pressure pulsation at different measuring points under several artesian flow conditions are obtained.The relationship between flow structure evolution and main frequency of pressure pulsation is also explored preliminarily.The research shows that the main characteristic frequency of pressure pulsation at each section is blade passing frequency and its second harmonic frequency.On the section of impeller inlet and rotating center,both the amplitudes of pressure pulsation at characteristic frequency and the RMS values in different frequency ranges mostly increase with the artesian flow rate increases.The energy of pressure pulsation under artesian flow condition is mainly concentrated in the frequency band of 0~500 Hz.The amplitude of pressure pulsation at blade passing frequency on the section of impeller inlet increases from hub to shroud.The amplitude of pressure pulsation on middle section of guide vane shows a trend of slow decrease and then sharp reduction from hub to shroud.The maximum amplitude of pressure pulsation in guide vane channel is located in the middle channel and the amplitude of pressure pulsation at blade passing frequency shows a decreasing trend with the artesian flow rate increases.The vortex structure evolution near leading edge of guide vane pressure surface is caused by rotor-stator interaction.The evolution of other unsteady vortex structures is the main hydraulic inducement for low-frequency discrete signals of pressure pulsation.4.The LMS multi-channel vibration and noise test system is used to collect and analyze the vibration acceleration signals at measuring points of pump under artesian flow condition.The spectrum characteristics of vibration acceleration under different artesian flow conditions are obtained.Both the RMS values of vibration acceleration in different frequency bands and the total vibration energy at each measuring point are analyzed and their trends with artesian flow rate are also discussed.The research shows that the wide-band excitation signals appear in every measured spectrum under artesian flow condition and its energy grow with the artesian flow rate increases.The RMS values of vibration acceleration in different frequency bands at each measuring point increase with the artesian flow rate increases,the values in different directions and the total vibration energy have the same trends with the artesian flow rate increases.The total vibration energy at outlet of guide vane will increase rapidly when the artesian flow rate is larger.