| This study is carried out under the financial support from National Science & Technology Pillar Program of China (2013BAK06B02). With the construction of ecological China and with the development of environmental governance, the single channel centrifugal pumps has been widely used in the sewage treatment and nonblocking convey. However, the the respect of the high energy consumption and poor running stability, there are still lots of difficults need to study. In order to improve the efficiency and running stability and further enrich and develop the design methods of the single channel pump, the unsteady characteristics and hydraulic design method are researched deeply in this study by the mehod of combining theoretical analysis, experimental tests and numerical calculations. The main work and creative achievements are summarized below:1. A synchronous experiment rig was established to investigate the pump performance and unsteady characteristics of the single channel pump. By using the test rig the energy performance, head pulsation, pressure fluctuation and radial force were conducted synchronously. It is found that (1) the unsteady characteristics of the single channel pump head is strong. At the design point, the pulsation of the head is 26.6% of the average head. (2) The impeller rotation angle when the minimum value of the head occurs increases from 43° to 60° as the operating point increases from 0.6Qd to 1.4Qd, while the impeller rotation angle when the maximum value of the head occurs decreases from 280° to 268°. (3) When the blade outlet edge just sweeps across the tongue, the pressure pulsation in the 8th section of the volute experiences a peak value. As the impeller rotation angle increases from 0° to 360°, the volute section where the peak pressure occurs decrasing from the 8th section to the 1st section. (4) The time-averaged radial force first decreases and then increases as the flow rates increases, with the minimum value occurring at the optimal operating point. When the operating flow rate increases from the 0.4Qd to 1.4AQd, the direction of the time-average radial force increases from 265° to 272° downstream the volute tongue.2. The CFD calculation method for simulating the complex internal flow of the single channel pump was verified based on the experiments. And the internal flow characteristics of the single channel impeller were analyzed. The results show that (1) to simulate the internal flow of the single channel pump the unsteady simulation method should be applied. For the simulations under small flow rates, the SST k-co model can be used, and the k-ε model can be used under other flow conditions. (2) When the impeller rotation angle increases from 0° to 325°, the circumferential locations of the high pressure zone at the impeller outlets rises from 40° to 330°, and the high pressure area is always located downstream of the blade outlets. (3) Under the low flow conditions, serious separation and recirculaton flow will occur within the flow passage of the blade pressure side.3. Considering the strong unsteady characteristics inside the single channel pump, the mathematical model for Busemann theoretical slip coefficients h0 and cm were established based on the assumption of single relative eddy by Backstrom. For the first time, a formula to solve slip factor within the full flow range for the single channel impeller was built. And the formula was verified by carring experiments on a single channel pump with a specific speed ns=140. It is concluded from the results that (1) the mathematical model has a good consistency with the theoretical solution. And the mathematical model for the slip coefficients ho is more accurate than the Wiesner method when β2B≥40°. (2) The calculation results for the slip factor by the formula agree well with the experimental data over the whole flow range, with the maximum deviation only 5.05%.4. By using the slip factor formula for the whole flow range and the energy loss model for the single channel pump, a energy performance prediction model for the single channel pump was established. And the prediction model was validated through the experiments on two single channel pumps. The results show that the head, power and efficiency of the single channel pump can be predicted accurately. The maximum deviation between the calculation results and the measured results is less than 6%.5. The hydraulic design method for the single channle impeller was improved. The maximum particle diamter, the head under design point and the maximum motor power were considered as the constraint condition for the design, and the highest efficiency of the pump was used as the objective function for the design process. Then the calulation methods for the main geometrical parameters of the single channle impeller were improved based on the energy performance prediction model. For the first time, a full monotonous blade profile function was proposed for the "thin-type" single channel impeller. A midline space function of the flow channel for the "thick-type" single channel impeller was proposed for the first time. By using the two functions, the drawing method for the single channel impeller was improved. Two single channel impellers were designed with the improved hydraulic method and the performance was compared with the similar products from home and abroad, the results show that the performance of the two impellers designed by the improved method has reached the international advanced level.6. The effects of the blade profile function, the blade outlet angle (β2B) and the blade wrap angle (εsb) on the energy performance were studied experimentally and numerically. The results show that (1) the mixing losses occurring at the impeller outlet and the internal hydraulic losses of the impeller can be reduced by using the monotonous blade profile function, by decreasing the β2B and by decreasing the blade outlet angle of the suction side β2SB-The internal hydraulic losses of the impeller decreases significantly and the mixing losses are less affected when the εsb is increased. (2) As β2B decreases, the head curve becomes steeper and the power curve shows non-overloading characteristic. (3) With β2B increasing from 8° to 25°, the head and power increases, and the efficiency firstly increases and then decreases. The maximum efficiency is increased by 7 percentage points. As β2B increases from 24° to 42°, the head and power increases, and the efficiency decreases. The maximum reduction of the efficiency is 1.8 percentage points. When εsb is increased from 290° to 390°, the power decreases, while the head and efficiency increases, the maximum increment of the efficiency is 7.79 percentage points.7. The effect of the blade outlet angle (β2B) and the blade wrap angle (εsb) on the head pulsation, the pressure fluctuation and the radial force were studied experimentally. The results show that (1) the temporal distribution of the maximum head and the direction of the radial force are mainly influenced by the blade outlet angle of the pressure side (β2PB), and are less affected by β2SB and εsb. With β2PB increasing from 8° to 25°, the maximum head becomes hysteresis gradually in the time domain, and the circumferential angle of the direction of the radial force decreases gradually. (2) As β2B increases from 8° to 25°, β2SB increases from 24° to 42° and εsb decreases from 390° to 290°, the head pulsation, the pressure fluctuation and the radial forces increase gradually. The decreasing order of the effects of the geometrical parameters on the head pulsation and pressure fluctuation is β2B>β2SB>εsb.b. For the radical force the order is β2SB>β2B>εsb.(3) In the case of ensuring the energy performance and the passage capacity for the particles, it can help to improve the pump unsteady characteristics and the operational stability by decreasing β2B,β2SB and by increasing εsb. |
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