# Dynamic Pressure Test and Analysis of Marine Ballasted Centrifugal Pump under Rapid Changing Conditions

^{*}

## Abstract

**:**

_{d}and 0.2× Q

_{d}, the rate of pressure increase is first fast and then slow. The dynamic pressure pulsation intensity is higher than the corresponding steady-state conditions after the transient conditions. With the increase in flow rate reduction, the characteristic frequencies of the dynamic pressure are 1APF (axial passing frequency) and 1BPF (blade passing frequency) and their harmonic frequency. The rapid decrease in flow rate causes the separation vortex in the impeller channel to be generated in advance, and the scale increases, which reduces the pulsation intensity of the pump outlet to prevent an increase in the level of broadband pulsation between 2APF and 1BPF.

## 1. Introduction

## 2. Experiment System and Scheme Design

#### 2.1. Research Object

_{d}= 32.6 m

^{3}/h, head H = 15.3 m, rotating speed n = 1450 r/min and the specific speed n

_{s}= 46. Its main geometric parameters are shown Table 1. As shown in Figure 1, the top and the outlet of the volute were chosen as monitoring points to monitor the inner dynamic pressure, respectively named as P1 and P2.

#### 2.2. The Experimental Design

#### 2.3. The Experimental Scheme

#### 2.4. Test Operating Steps

_{d}condition, and start to collect dynamic pressure before the pneumatic control valve starts to execute the output signal. After sampling, the PLC controller returns to the original signal. Repeat the above operations to complete the test of S2, S3 and S4. Finally, slowly turn off the inverter after completing all the test.

## 3. Results and Analysis

#### 3.1. Time Domain Analysis of Pressure Fluctuation during the Rapid Reduction of Flow Rate

_{d}to 0.8× Q

_{d}, the pressure at P1 gradually increases. As the amplitude of the decreasing flow rate increases, the pressure at P1 shows firstly a rapid increase and then a slow increase. The times of rapid increase are 1.2 s, 0.8 s and 0.6 s, respectively, which means that the larger the amplitude of the flow rate change is, the faster the pressure increases.

_{d}to 0.8× Q

_{d}, pressure at P2 increases uniformly. As the amplitude of the decreasing flow rate increases, the pressure at P2 shows firstly a rapid increase, followed by a slow increase, and the trend is consistent with P1.

_{d}, 0.6× Q

_{d}, 0.4× Q

_{d}and 0.2× Q

_{d}, respectively, to analyse the steady dynamic pressure in the pump. The statistical data are shown in Figure 6. It can be seen from Figure 6 that the standard deviation of the dynamic pressure after the transient conditions of P1 and P2 is higher than the corresponding steady-state operating conditions. Meanwhile, the rapid change in flow leads to an increase in the amplitude of pressure pulsation, and enhances the internal turbulent flow characteristics. With the increase in flow rate change, the standard deviation of the dynamic pressure after the transient conditions becomes smaller and smaller. The rapid decrease in flow rate causes the relative velocity of the fluid in the impeller to decrease, and the effect of the dynamic and static interference between the fluid and the volute is weakened, which results in a decrease in the intensity of dynamic pressure pulsation.

#### 3.2. Dynamic Pressure Frequency Analysis

- (1)
- The frequency analysis of the dynamic pressure for P1

- (2)
- The frequency analysis of the rapid reduction in flow rate for P2

#### 3.3. The Analysis of Inner Flow by Numerical Simulation Caiculation

_{d}, 0.6× Q

_{d}, 0.4× Q

_{d}, 0.2× Q

_{d}are chosen to analyze inner flow. Figure 10 and the Figure 11 show the pressure and streamline at the middle plane of the impeller.

_{d}, the meridian velocity of the fluid near the pressure surface of the blade and shear force continuously decreases. A separation of the vortices then occurs in the middle of the pressure surface of passage 2. However, no obvious reflux for the 0.8× Q

_{d}of the steady conditions has yet occurred in the impeller. For S2, when the flow rate is rapidly reduced to 0.6× Q

_{d}, the separation vortex structure appears in the middle position of the blade pressure surface in flow passages 1, 2, and 6, and the size of the separation vortex is significantly larger than the corresponding 0.6× Q

_{d}steady-state condition. For S3 and S4, the size of the separation vortex in the flow channel is also significantly larger than the corresponding steady-state operating condition, because as the flow rate change increases, the relative velocity of the fluid particles in the flow channel continues to decrease, and the absolute velocity continues to increase. This in turn increases the imbalance between the Coriolis force and circumferential pressure of the surrounding fluid particles, meaning the generation of separation vortices and the continuous increase in scale. The larger-scale separating vortex squeezes the fluid in the flow channel, which leads to an increase in the energy of the jet at the outlet of the impeller, and an increase in the pulsation intensity of 1BPF at P1. However, the larger scale backflows move to the impeller outlet under transient conditions, which then has a collision with the tongue of the volute, which decreases the strength of the interaction between the jet form impeller outlet and tongue. Therefore, the amplitude of 1BPF at P2 is reduced, and is lower than the corresponding steady conditions. The rapid change in flow has caused an increase in the uneven distribution of the impeller outlet pressure, and it reflects that the dynamic pressure pulsation of the impeller outlet does not have an obvious characteristic frequency, thus causing an increasing pulsation level of the broadband frequency between 2APF and 1BPF.

## 4. Conclusions

- The dynamic pressure in the ballast pump periodically increases. The larger the amplitude of the flow reduction is, the greater the rate of the pressure increase. While the flow rate rapidly decreases to 0.4× Q
_{d}and 0.2× Q_{d}, the pressure builds up quickly and then slowly. - The dynamic pressure pulsation intensity of each transient scheme is higher than the corresponding steady-state conditions after the transient conditions. With the rapid reduction in the flow rate, the dominant frequencies of the dynamic pressure are 1APF and 1BPF and their harmonic frequencies.
- The rapid reduction in flow rate accelerates the separation of the vortex in the impeller channel, which shows that the separating vortexes are generated in advance, and their scale increases, which in turn reduces the pulsation intensity of the pump outlet and also causes an increase in the level of broadband pulsation between 2APF and 1BPF.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 2.**Sketch diagram of the experimental system for rapid reduction of flow rate. 1 Model pump, 2 Pressure sensor, 3 PLC controller, 4 Data collection systems, 5 Computer, 6 Electromagnetic flowmeter, 7 Pneumatic control valve, 8 Air compressor, 9 Backwater valve, 10 Water tank, 11 Vent hole, 12 Inlet hole, 13 Level gauge, 14 Drain valve, 15 Water outlet valve, 16 Base.

**Figure 6.**The standard deviation of dynamic pressure of transient and steady conditions at (

**a**) P1 and (

**b**) P2.

**Figure 7.**Frequency distribution at P1 under each (

**a**) Steady conditions and (

**b**) Transient conditions.

**Figure 9.**Frequency distribution at P2 under each (

**a**) Steady conditions and (

**b**) Transient conditions.

**Figure 11.**The pressure and streamline distribution in impeller under steady conditions (

**a**) 0.8× Q

_{d}, (

**b**) 0.6× Q

_{d}, (

**c**) 0.4× Q

_{d}and (

**d**) 0.2× Q

_{d}.

**Figure 12.**Pressure and streamline distribution in impeller after rapid change conditions (

**a**) 0.8× Q

_{d}, (

**b**) 0.6× Q

_{d}, (

**c**) 0.4× Q

_{d}and (

**d**) 0.2× Q

_{d}.

Overflow Component | Geometric Parameters/Unit | Symbol | Value |
---|---|---|---|

Impeller | Inlet diameter/mm | D_{1} | 65 |

Outlet diameter/mm | D_{2} | 214 | |

Outlet width/mm | b_{1} | 8 | |

Blade number | Z | 6 | |

Volute | Diameter of basic circle/mm | D_{3} | 240 |

Inlet width/mm | b_{2} | 20 | |

Outlet diameter/mm | D_{4} | 50 |

Parameters | Value |
---|---|

Measuring range | 0–1 MPa |

Output signal | 4–20 mA |

Precision grade | 0.25% Fs |

Power supply | 10–28 VDC |

Working condition | −10–80 °C |

Experimental Schemes | |||
---|---|---|---|

S1 | S2 | S3 | S4 |

1.0× Q_{d}–0.8× Q_{d} | 1.0× Q_{d}–0.6× Q_{d} | 1.0× Q_{d}–0.4× Q_{d} | 1.0× Q_{d}–0.2× Q_{d} |

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**MDPI and ACS Style**

Zhu, Z.; Liu, H.
Dynamic Pressure Test and Analysis of Marine Ballasted Centrifugal Pump under Rapid Changing Conditions. *J. Mar. Sci. Eng.* **2021**, *9*, 1299.
https://doi.org/10.3390/jmse9111299

**AMA Style**

Zhu Z, Liu H.
Dynamic Pressure Test and Analysis of Marine Ballasted Centrifugal Pump under Rapid Changing Conditions. *Journal of Marine Science and Engineering*. 2021; 9(11):1299.
https://doi.org/10.3390/jmse9111299

**Chicago/Turabian Style**

Zhu, Zhipeng, and Houlin Liu.
2021. "Dynamic Pressure Test and Analysis of Marine Ballasted Centrifugal Pump under Rapid Changing Conditions" *Journal of Marine Science and Engineering* 9, no. 11: 1299.
https://doi.org/10.3390/jmse9111299