The influence of front guide vane adjustment on the function of water pump and its use control

Abstract: The second phase of the water diversion project of the upper reaches of the Huangpu River in Shanghai used 12 large vertical mixed-flow pumps, all of which were equipped with an Inlet Vane Conttrol Device VR (Inlet Vane Conttrol Device VR) manufactured by KSB in Germany in front of the impeller. Adjust the performance of the pump in a wide range.
Key words: Front guide vane pump performance Guide vane angle 1 Introduction Shanghai Huangpu River upstream water diversion project Phase II uses 12 large vertical mixed flow pumps, all of which are equipped with front guide vane devices made by German KSB company in front of their impellers (Inlet Vane Conttrol Device VR), the purpose is to adjust the performance of the pump in a wide range. The pump group structure is shown in Figure 1. Its parameters are: flow Q=6.5M3/S, head H=15.5M, speed n=297rpm, comparison number ns=353, efficiency η=0.80, shaft power P=1400KW. The front guide vane device (VR device for short) is currently not widely used in domestic and foreign water pumps, and there are few technical data and reports in this regard. To this end, the author, based on the observation of the pump operation and related test data and technical data in the past three years, has made some analysis and research on the impact and reasons of the use and adjustment of the VR device on the performance of the pump, so as to have a more objective and correct understanding of the VR device. , So as to put forward some reference opinions on the actual use control of this type of pump. The influence of two-front guide vane device on the performance of water pump
　　The VR device we use is circular, the guide vanes are straight-blade type, a total of 17 pieces, the blade length is 500mm, and the device diameter is 1300mm, as shown in Figure 2. The device is driven by a motor, and the torque is transmitted to the input shaft of the device through a multi-section transmission rod equipped with a universal joint, and then the blades are rotated synchronously through the gear system in the device to achieve the purpose of adjusting the angle of the guide vane. KSB company set that the VR device guide vane is perpendicular to the horizontal plane as 90º, when the blade rotation and tilt direction is consistent with the pump impeller rotation direction, the angle is reduced (that is, the angle becomes smaller); when the blade tilt direction is opposite to the pump impeller rotation direction To increase the angle (that is, the angle becomes larger). The following first analyzes the impact of the installation of the front guide vane on the water pump and the performance of the water pump. (1) Comparison of pump performance when the front guide vane is not installed and when the front guide vane is installed and the blade angle is 90º When the blades and blades are at 90º, the characteristic curves are compared with those of the pump without the front guide vane device, as shown in Figure 3. From the figure, we can draw the following conclusions: 1. The Q-H curve of the pump without the front guide vane and the front guide vane 90 º is basically two parallel curves, with the front guide vane Q- The –H curve is slightly lower, which is due to the increase in the resistance loss of the inlet liquid flow after the front guide vane is added, which causes the head to drop. 2. It can be seen from the Q-η curve that the two curves are basically close, and there is a coincidence point. To the left of this point, the Q-η curve with the leading vane is slightly higher than the Q-η curve without the leading vane. 3 On the right side of this point, the Q-η curve with the leading vane is slightly lower than the Q-η curve without the leading vane, and this coincidence point is the optimal operating point. This shows that under the optimal working conditions, the resistance loss of the front guide vane is very small for the pump and does not cause any impact; and at low flow, due to the small flow in the inlet pipe, the flow is uneven, and the front guide vane is added. After the guide vane, it plays a role of diversion to enhance the uniformity of the flow at the inlet of the liquid stream, and the efficiency is improved compared with the original. When the flow is large, the diversion effect disappears. On the contrary, due to the increase of the front guide vane, the resistance loss increases. Resulting in a decrease in efficiency. It can be seen that when the guide vane position is at 90 º At this time, the performance of the pump is basically similar to that of the pump without front guide vane. At this time, it has little effect on the characteristics of the pump. Secondly, let’s take a look at the changes in pump performance when the guide vanes are at different angles. (2) The influence of VR device guide vane on pump performance at different angles 1 The influence on Q-H performance curve Figure 4 is the performance curve of the pump with VR device under various guide vane angles. It can be seen from Figure 4 that when the front guide vane is adjusted to a direction less than 90, the performance curve obtained is obviously to the left, and moves substantially parallel to the performance curve at 90 º (at the continuous operating limit Within range). This is because at this time, the direction of the liquid flow at the outlet of the front guide vane and the direction of rotation of the impeller tends to be the same, and the liquid flow has a positive pre-rotation Vlu before the entrance of the impeller of the pump. ), so Vlu>0 (when the front guide vane is 90º., Vlu=0). From Euler’s equation: HT=(u2v2u-ulvlu)/g, it is known that when the angle of the guide vane is less than 90º. When the direction is adjusted, since Vlu>0, the theoretical head HT of the pump is smaller than that of the guide vane. Hour pump head HT. And, the smaller the value of the front guide vane angle, the larger the value of Vlu, the larger the head drop, so the Q-H characteristic curve shifts to the left. In actual use, it is precisely this feature that keeps the head basically constant, so that the flow rate becomes smaller as the VR angle becomes smaller, so as to achieve the purpose of reducing the flow rate. While the current guide vane is greater than 90º direction adjustment, at this time, the direction of the liquid outlet of the front guide vane is opposite to the direction of rotation of the impeller, that is, reverse pre-rotation occurs, so Vlu<0. It can also be known from Euler’s equation that the head HT of the pump at this time is greater than the head of the front guide vane at 90°. Moreover, the greater the front guide vane angle, the smaller the Vlu, the greater the increase in pump head, and the Q-H characteristic curve shifts to the right. Therefore, under a certain head, the flow rate of the pump can be increased as the angle of the guide vane becomes larger. Practice shows that the above-mentioned effects are obvious. 2 The influence on the efficiency η of the water pump is due to the front guide vane direction 90º The two sides of the position are adjusted, so that the liquid flow produces forward and reverse pre-rotation before entering the pump impeller. The circumferential component Vlu of the absolute velocity V1 is generated at the inlet of the impeller blade, so that the impeller inlet velocity triangle is changed, as shown in the figure. 5 shown. The solid line is the velocity triangle without pre-spin, and the dotted line is the velocity triangle with forward pre-spin and reverse pre-spin. It can be seen from the figure that the relative speed ω1 under the three conditions is different. ω′1 is the relative speed when the liquid flow is pre-swirled in the forward direction; ω″1 is the relative speed when the liquid flow is pre-swirled in the reverse direction. Obviously. ω1 increases with the increase of the guide vane angle. From Figure 6, we can clearly see that the adjustment of the front guide vane angle has an obvious influence on the pump efficiency. When the guide vane is at the 90º position, the pump runs The range of the high efficiency zone is the largest and the efficiency is the highest. When the angle of the guide vane gradually increases or decreases, the operating efficiency of the pump also gradually decreases. Moreover, the farther the guide vane angle deviates from 90º the position, the greater and more obvious the drop in efficiency, which makes the pump Can not operate normally. Therefore, we limit the adjustment angle of the pump’s front guide vane to 75º—110º. Within the range, so that the pump can operate safely within the efficiency range of more than 75%. At 75º—110º ; Within the range, the operating efficiency of the pump changes. According to our analysis of the test data, there are the following rules: When the guide vane is adjusted within the range of 75º—-95º, the operating efficiency of the pump changes less. And the efficiency is higher; and once the guide vane is adjusted in the direction greater than 95º, the pump efficiency will obviously accelerate and drop. Table 1 is the test data of the operating efficiency of three pumps of the same type under different guide vane angles: Table 1 Different guide vanes Test data of pump operating efficiency at different angles Guide vane angle 75º 80º 85º 90º 95º 100º 105º 110º A pump efficiency% 81.82 82.22 82.51 82.70 81.76 80.25 77.89 76.10 B pump efficiency% 85.62 85.73 85.08 82.01 84.83 77. 43 C pump efficiency% 88.50 87.36 87.40 86.92 85.80 84.47 8107 79.25 The reasons for the above phenomenon can be analyzed by Euler’s equation and velocity triangle: from the foregoing we know that 75º—110º. Within the range, when the guide vane is adjusted in the direction of less than 90°, the liquid flow will produce positive pre-rotation Vlu, which will reduce the theoretical energy head HT of the pump. However, due to the reduction of the relative speed ω1, the impact loss of the liquid flow on the impeller is greatly reduced, so the efficiency of the pump is not significantly reduced; on the contrary, when the guide vane angle is adjusted in the direction greater than 90º, although the liquid flow produces anti-prediction Rotating Vlu improves the theoretical energy HT. However, due to the increase of the relative speed ω1, the impact loss of the liquid flow on the impeller is increased, so the efficiency is relatively significantly reduced. If the guide vane angle is adjusted outside the limit, the flow will deviate from the design flow Qd, the attack angle of the liquid flow. When the change occurs, a vortex area will be formed on the working surface of the impeller blades, causing greater impact loss and lower pump efficiency. In summary, we believe that: the adjustment of the front guide vane causes the efficiency of the pump to change, and the pre-rotation of the liquid flow and the impact loss to the impeller are the main factors. Therefore, the adjustment of the front guide vane is limited. Even in the limited 75º one 110º Within the scope of use, the pump should also be avoided from running at the extreme angle for a long time. 3 The impact on the cavitation performance of the water pump is obvious. When the front guide vane is adjusted in a direction greater than 90, the liquid flow produces reverse pre-rotation, which increases the relative velocity ω1 of the liquid flow at the pump impeller inlet, and the liquid flow produces the impeller. The impact effect, as the angle of the guide vane increases, the impact becomes more serious, which has an adverse effect on the cavitation performance of the water pump. According to the basic equation of water pump cavitation: NPSHr=λ1V20/2g ten λ2ω12/2g, it is known that due to the increase of relative velocity ω1, the necessary cavitation allowance NPSHr is greatly increased, which reduces the cavitation performance of the water pump. Therefore, in operation and use, the angle of the guide vane should be adjusted according to the cavitation characteristic curve of the pump and the changes in water level and head to ensure that the effective NPSH NPSHa is greater than the required NPSHr. In addition, due to the impact of the liquid flow on the impeller, the vibration value at the impeller of the water pump also increases as the angle of the guide vane increases. Table 2 shows the corresponding values ​​of the angle change of the front guide vane and the vibration value at the impeller when a certain pump is at a certain water level. Table 2 Corresponding changes in the front guide vane angle and the vibration value at the impeller. Guide vane angle 75º 80º 85º 90º 95º 100º 105º 110º Vibration value (mm/s) 1.87 1.90 1.93 2.01 2.08 2.19 2.24 2.55 Three conclusions The adjustment of the front guide vane of the water pump can effectively change the operating conditions of the water pump and meet the requirements of production and use to a greater extent. At the same time, due to the adjustment of the guide vanes, the direction of the liquid flow changes, so that the impact of the liquid flow on the impeller and the energy head loss increase, resulting in a decrease in the operating efficiency of the pump, and affecting the cavitation performance of the pump. However, as long as the adjustment range of the guide vane is limited to an appropriate area, its negative effects 55 Concluding remarks The adjustment of the front guide vane of the water pump can effectively change the operating conditions of the water pump and meet the requirements of production and use to a large extent. At the same time, due to the adjustment of the guide vanes, the direction of the liquid flow changes, so that the impact of the liquid flow on the impeller and the energy head loss increase, resulting in a decrease in the operating efficiency of the pump, and affecting the cavitation performance of the pump. However, as long as the adjustment range of the guide vane is limited to an appropriate area, its negative effects 55 Concluding remarks The adjustment of the front guide vane of the water pump can effectively change the operating conditions of the water pump and meet the requirements of production and use to a large extent. At the same time, due to the adjustment of the guide vanes, the direction of the liquid flow changes, so that the impact of the liquid flow on the impeller and the energy head loss increase, resulting in a decrease in the operating efficiency of the pump, and affecting the cavitation performance of the pump. However, as long as the adjustment range of the guide vane is limited to an appropriate area, its negative effects