Frequency Of Pressure Pulsation Research Articles

Transient flow structures and pressure pulsations of a high-pressure aero-fuel centrifugal pump

In order to study the complex transient flow characteristics of a high-pressure aero-fuel centrifugal pump within its full working envelope, a certain type of centrifugal pump is numerically simulated, in which the simulation results are compared with the experiment results to verify the effectiveness of the present simulation method. Then, the verified simulation method is selected to analyze the transient flow characteristics, in which the time-frequency characteristic of pressure pulsation at monitored positions is analyzed by using fast fourier transform. In addition, the unsteady flow structures are studied by focusing on the relative speed, turbulent kinetic energy and so on. The results show that the main frequency of pressure pulsation in the impeller and volute is rotation frequency and blade frequency, respectively, where different monitoring points show similar trend. Meanwhile, the flow is relatively stable under design flow rate condition. However, a certain large-scale vortex appears in the impeller channel under small flow rate conditions, which mainly exists at the exit of the impeller channel near the tongue. In addition, turbulent kinetic energy at the exit of the impeller and the tongue has a large distribution range and changes seriously, where a certain hydraulic loss is produced.

Numerical analysis of pressure pulsation in vertical submersible axial flow pump device under bidirectional operation

In order to analyze the pressure pulsation characteristics of a single-conduit vertical submersible axial-flow pump device under bidirectional operation, the unsteady numerical simulation of the pump device was carried out based on computational fluid dynamics. The pressure pulsation coefficient and fast Fourier transform were used to analyze the pulsation of each monitoring point in the time–frequency domain. The results show that the pressure pulsation at different positions of the pump device is mainly affected by the impeller rotation, and the amplitude is large at the blade frequency and its harmonic frequency. In the positive operation, the main frequency of pressure pulsation at each monitoring point at the inlet of the impeller is three times the rotating frequency, and in the reverse operation, the main frequency of pressure pulsation at each monitoring point is 0.5 times the rotating frequency. The amplitude of pressure pulsation at each monitoring point at the inlet of the impeller is less than that of the positive operation, while the amplitude of pressure pulsation at the outlet of the impeller and the guide vane is larger than that of the positive operation. In the positive and reverse operation, the axial force of the impeller is significantly affected by the inlet velocity, and the amplitude of the axial force is small in the rotation period. The axial force increases with the increase of flow rate. The radial force of the impeller is significantly affected by the inflow flow pattern. The radial force changes obviously in the rotation period, and the radial force does not change regularly with the flow rate. The radial force of the impeller under reverse operation is 7.75 times that under positive operation.

Influence of the hydrofoil trailing-edge shape on the temporal-spatial features of vortex shedding

Ocean energy is a kind of clean and valuable renewable resource, which can be efficient utilized through turbomachinery. The turbulent pulsation effect and unsteady flow regime will cause pressure pulsation which can destroy the stability of the unit, especially at the tailing edge of blade. This paper compares pressure field change in the downstream region with different trailing edge geometry by numerical simulation and the pulsation tracking network method. The reasons for weakening downstream pressure pulsation with the Donaldson modification and the propagation law of the pressure pulsation are clarified. By Donaldson modification, the main frequency of pressure pulsation becomes the frequency of vortex shedding (fvs) and the amplitude is reduced to 10% of the original value. The propagation law of pressure pulsation has changed and the scope of influence has been expanded. The position of vortex generation can be judged by the phase variation. The weakening of the fvs amplitude is due to the stable low-pressure region and the phase difference variation. The inhibition of the convergence effect of vortex causes the weakening of the 2fvs amplitude. This study provides an effective method and reference for understanding the downstream pressure pulsation variation of shedding vortex.

Study on the pressure pipe length in train aerodynamic tests and its applications in crosswinds

The pressure integral method is frequently used to obtain the train aerodynamic forces in experiments, but the effect of the pressure pipe length on the pressure amplitude is not understood. In this paper, based on field tests without pressure pipes, the dominant frequency (DF) ranges of the pressure pulsations on the train surface under various conditions, including open-air, crosswind, and tunnel conditions, were analyzed. Then the effect of the pressure pipe length on the pressure amplitude with various pulsation frequencies was investigated. Finally, in a full-scale test under crosswinds, the selected pressure pipe length was applied to verify its reliability and to study the train aerodynamic performance. The results showed that the maximum DF occurred when two trains passed each other (near 60 Hz), and the DF under crosswinds was the smallest (less than 1 Hz). When the pressure pulsation frequency was less than 1 Hz, the error range of the pressure amplitude was less than 5% with a pressure pipe length of ≤8 m. The pressure pipe is a polyvinyl chloride (PVC) pipe with an outer diameter of 2 mm and an inner diameter of 1.8 mm. The full-scale test results for the windproof ability of different windbreak walls and the aerodynamic forces of the train showed that the current pressure pipe length was reasonable and could reflect the actual operating conditions of the train under crosswinds.

Experimental Investigation of Unsteady Pressure Pulsation in New Type Dishwasher Pump with Special Double-Tongue Volute

A pressure pulsation experiment of a dishwasher pump with a passive rotation double-tongue volute was carried out and compared with the pressure pulsation of a single-tongue volute and a static double-tongue volute. The pressure pulsation of the three volute models was compared and analyzed from two aspects of different impeller speeds and different monitoring points. The frequency domain and time–frequency domain of pressure pulsation were obtained by a Fourier transform and short-time Fourier transform, respectively. The results showed that the average pressure of each monitoring point on the rotating double-tongue volute was the smallest and that on the single-tongue volute was the largest. When the impeller rotates at 3000 rpm, there were eight peaks and valleys in the pressure pulsation time domain curve of the single-tongue volute, while the double-tongue volute was twice that of the single-tongue volute. Under different impeller speeds, the changing trends of pressure pulsation time and frequency domain curves of static and rotating double-tongue volutes at monitoring point p1 are basically the same. Therefore, a volute reference scheme with passive rotation speed is proposed in this study, which can effectively improve the flow pattern and reduce pressure inside the dishwasher pump, and also provide a new idea for rotor–rotor interference to guide the innovation of dishwashers.

Experimental Study on Flow Behavior of Unshrouded Impeller Centrifugal Pumps under Inlet Air Entrainment Condition

Results on overall pump head and efficiency performance, pressure pulsation and high speed camera visualization of flow patterns behavior are presented for different inlet air-water void fractions at a given rotational speed. With the increase of inlet void fractions and decrease of the flow rates, the size of bubbles increase and tend to agglomerate in specific impeller passage locations along the blade chord. The starting point of pump breakdown is related to a strong inward reverse flow occurring in a specific location near the shroud gap of the impeller and volute tongue region. Using a constant air void fraction value of 2%, pressure pulsation frequency results are analyzed in relation with local flow mixture patterns and flow rate modification.

Numerical simulation of air injection in part load operating point

The operation hydro turbines in the off-design operating points is often accompanied by pressure pulsations with a large amplitude. One way to deal with such pulsations is to inject the air into hydro turbine flow passage. The aim of this work is to simulate this process. Previously we carried out calculations in frames of homogeneous incompressible three-phase «liquid – vapor – non-condensable gas» mixture model. The computational domain consisted of wicket gate, runner and draft tube. The wicket gate and runner were considered in the periodic stage approach. The results obtained were in good agreement with experimental data at full load operating point. It was shown that the calculations on the previous model failed to accurately simulate influence of air flow rate on the amplitude and frequency of pressure pulsations in part load. Therefore the part load regime is studied carefully in this work: different computational domains are considered, different solvers are used, including ANSYS CFX and CADRUN, developed at the Institute of Computational Technologies. Different models of «liquid – gas» mixture are used in the calculations, compressibility is also taken into account. The flow rate of the injected air ranged from 0.5 to 2 percent of the water flow rate. The influence of the injected air on the flow pattern, including the vortex rope, is investigated. The results obtained are compared with experimental data.

Special Pressure Fluctuation analyse of the pump turbine

In the 13th five-year planning, the pumped storage power stations have speeding up. A large number of pumped storage power stations will been installed. The current development of modern pump storage plants aims towards a higher flexibility and stability in operation, an extended operation range of the hydraulic machine. The stability of pump turbine has been paid more and more attention in the industry.Hydraulic pressure pulsation is very important for the stability of pump turbine. For pump turbine, the pressure pulsation on vane-less area between guide vane and runner blade is very important. It is the fundamental source of unit stability and the direct embodiment of rotational and static interference.This paper analyses the special pressure pulsation in the vane-less area of pump turbine, focusing on the pressure pulsation of one time rotating frequency and two times rotating frequency.The amplitude and frequency of pressure pulsation and the source of pressure pulsation induced by this special frequency are analysed and detected from the perspective of numerical and model test. By optimizing the design of the runner, the pressure pulsation of that particular frequency is eliminated.

Experimental study on pressure fluctuation characteristics of model pump in Huangjinxia hydro-junction

In this study, the pressure pulsation characteristics of different position in the model pump unit are studied by experiments in combination with the Huangjinxia hydro-junction. The pressure pulsation of the inlet pipe, the volute outlet and the area between impeller and guide vane under different operating conditions were measured and analyzed. The results show that the maximum pressure pulsation amplitude of the pump is less than the guaranteed values by comparing the test results with the value requirement of the pump, which ensures the safe and stable operation of the pump. FFT transform is used to analyze the main frequency and amplitude of pressure pulsation. The main frequency and secondary frequency at the impeller inlet are respectively 15.29 and 7.65 times of the rotating frequency, which are 2 and 1 times of the blade frequency. The amplitude of main frequency at each monitoring point increases with the increase of head. The test results of pressure pulsation value meet the requirements of the contract in the whole pump operation rang.

Effect of bend radius and insulation on adiabatic section on the performance of a single closed loop pulsating heat pipe: experimental study and heat transfer correlation

Pulsating heat pipes are a relatively newer generation of heat pipe which are wickless thus more economical and less fabrication-intensive. These devices are made of a capillary sized tube bent in a serpentine form to result in a closed system. In this study a single closed loop pulsating heat pipe made of 2 mm internal diameter copper tubing is experimentally investigated for two different bend radii. The performance comparison is made for two fluids – methanol and water, for varying heat loads from 10 W to 100 W, with various inclinations from vertical bottom heated mode to horizontal mode, for a constant fill ratio of 60%. The sharper bend, though making the device more compact, is found to reduce the performance. One of the bend geometries is further investigated for the effect of insulation on the adiabatic sections. The insulation is found to certainly widen the heat load range though a distinct performance improvement is not found. The variation of the frequency of pressure pulsations with respect to the fluid, heat load and inclination is also studied. Additionally, one of the geometry is tested with FC 72 fluid as well to arrive at a correlation for heat flux for varying fluids, heat fluxes and inclinations, covering 116 data points. The performance trends predicted by the correlation are in line with those reported in the literature.

Clocking effect of outlet RGVs on hydrodynamic characteristics in a centrifugal pump with an inlet inducer by CFD method

This paper investigates the hydrodynamic characteristic of a single-stage centrifugal pump with inlet inducer and outlet Radial Guided Vanes (RGVs) influenced by the clocking effect for the first time. Different from general ones, the outlet RGVs in this paper have specificities. The hydraulic performance and dynamic characteristics of the centrifugal pump are numerically studied and validated by experiments. The results indicate that there is an optimum position of RGVs that can not only increase the pump head and efficiency but also reduce the pressure fluctuation intensity. A non-dimensional parameter describing the velocity non-uniformity of the impeller outlet is first proposed, which is negatively related to the pump’s hydraulic performance. The clocking position of the RGVs will affect the velocity homogeneity at the impeller outlet, and further influence the hydraulic characteristics of the pump. Besides, the clocking effect of outlet RGVs mainly affects the amplitudes of BPF for both the pressure fluctuation and radial force, and the most obvious frequency of pressure pulsation and radial force is 3 BPF correlating with the inlet inducer. It is recommended to install the volute-tongue tip near the middle of two vanes.

Performance of water-jet pump under acceleration

The instantaneous acceleration affects the performance of the water-jet pump obviously. Here, based on the user-defined function, the method to simulate the inner flow in water-jet pumps under acceleration conditions was established. The effects of two different acceleration modes (linear acceleration and exponential acceleration) and three kinds of different acceleration time (0.5s, 1s and 2s) on the performance of the water-jet pump were analyzed. The results show that the thrust and the pressure pulsation under exponential acceleration are lower than that under linear acceleration at the same time; the vapor volume fraction in the impeller under linear acceleration is 27.3% higher than that under exponential acceleration. As the acceleration time increases, the thrust gradually increases and the pressure pulsation amplitude at the impeller inlet and outlet gradually decreases, while the law of pressure pulsation is the opposite at the diffuser outlet. The main frequency of pressure pulsation at the impeller outlet is different under different acceleration time. The research results can provide some reference for the optimal design of water-jet pumps.

Variations of Performance and Pressure Pulsation During Cavitation in Centrifugal Pumps with Entrained Air

Most of the research on the cavitation with entrained air has focused on the military direction, but it ,about centrifugal pumps, which is relevant to people's livelihood, is still relatively lacking. In order to study the basic law of the development of cavitation inside centrifugal pumps under aeration conditions, a test bench suitable for cavitation experiments with incoming flow containing gas was obtained. Furthermore, a single-stage single-suction 6-blade centrifugal pump was used as the research object to conduct pressure pulsation experiments under cavitation condition when the incoming flow was 1.0% air viod fraction at 2900r/min-50m3/h. The results showed that: After cavitation happened, the greater aeration content will deteriorate the pump's anti-cavitation performance, but the head curve is more gentle in falling down compared to natural cavitation. Hence aeration has a beneficial effect on the performance degradation of the pump under the cavitation condition. At the same time, before the cavitation number drops to the fracture cavitation number of the pump, aeration has improvement in the efficiency of the pump in different degrees , especially in the situation with the ventilated rate of 1.0%. The main frequency of pressure pulsation at the inlet and outlet of the test pump after aeration is dominated by the blade frequency. The shaft frequency signal at the outlet gradually decreases with the cavitation number lessened. Moreover the amplitude of the blade frequency grows slightly with the reduction of the cavitation number. But it tends to soar when the cavitation number is less than the fracture cavitation number.

Vibration Diagnosis and Treatment for a Scrubber System Connected to a Reciprocating Compressor

Severe vibration was observed at a scrubber system connected to a reciprocating compressor during commissioning stage. Field measurements including vibration, pressure pulsation, and modal experiment were conducted to determine the causes of vibration, which showed that the excessive vibration was caused by pressure pulsation-induced mechanical resonance. Vibration reduction treatment for mechanical resonance avoidance via the installation of support on scrubber was proposed and then validated by resonance analysis and one-way fluid structure interaction (FSI) analysis. Resonance analysis showed both the dominant frequencies of pressure pulsation and rotational frequencies of compressor were beyond resonance regions, and FSI analysis indicated that the vibration levels of the scrubber system at its design conditions were within the allowable limit. Installation of two braces with a band clamp on the scrubber was implemented. The effectiveness of the treatment was verified by comparison of measured data before and after scrubber modification; the peak amplitudes occurring at the dominant excitation frequencies in both vibration and pulsation spectra declined greatly after modification, which guaranteed the long-term stable operation of the scrubber.

Improvement of Intake Structures in a Two-Way Pumping Station with Experimental Analysis

Pumping stations are important regulation facilities in a water distribution system. Intake structures can generally have a great influence on the operational state of the pumping station. To analyze the effects of the bell mouth height of the two-way intake on the performance characteristics and the pressure pulsations of a two-way pumping station, the laboratory-sized model pump units with three different intakes were experimentally investigated. To facilitate parameterized control, ellipse and straight lines were used to construct the profile of the bell mouth. The frequency domain and time-frequency domain of the pressure pulsations on the wall of intakes were analyzed by the Welch’s power spectral density estimate and the continuous wavelet transform (CWT) methods, respectively. The results showed that the bell mouth height (H) has significant influences on the uniformity of the impeller inflow and the operation stability of the pump unit. When H = 204 mm, the data fluctuated greatly throughout the test process and the performance curves are slightly lower than the other two schemes. As the bell mouth height gradually decreases, the average pressure difference of each measuring point began to decrease, more homogeneous velocity distribution of impeller inflow can be ensured. The amplitude of blade passing frequency is obvious in the spectrum. While when (H) is more than 164 mm, the main frequency of pressure pulsations at three points fluctuates with the rotation of the impeller. When H decreases to 142 mm, pressure pulsations will be independent of the operating conditions and positions which contributes to the long-term stable operation of the pump unit.

System Design and Characteristic Analysis of Follow-up Hydraulic Muffler Based on Gear-Screw Transmission

In order to improve the attenuation frequency range of traditional static two-stage H-type hydraulic muffler, a two-stage follow-up hydraulic muffler driven by gear-screw is designed based on PLC. The Muffler can change its structure parameters according to the rotational speed of the hydraulic pump, and attenuate the two pulsation frequencies of the hydraulic pump. Considering the structural parameters and gear transmission of the muffler, the static and dynamic characteristics of the muffler are analyzed systematically, and the stability of the muffler is verified by the case simulation test. The results show that the two-stage follow-up hydraulic muffler based on PLC can attenuate the two pressure pulsation frequencies at the same time, and the operation is stable and the response speed is fast. The two-stage follow-up hydraulic muffler has practical significance and value to provides a way for engineering hydraulic system noise reduction.

Spinning behavior of flow-acoustic resonant fields inside a cavity: Vortex-shedding modes and diametral acoustic modes

The spinning behavior of flow-acoustic resonant fields inside an axisymmetric cavity configuration was numerically investigated in four flow conditions containing different resonances between vortex-shedding modes and diametral acoustic modes. Zonal large-eddy simulations (ZLESs) were conducted to determine the aeroacoustic and aerodynamic fields simultaneously. In the ZLESs, a shear stress transport turbulence model was used to model the relatively steady flow field inside the inlet and outlet sections. Simultaneously, the wall-modeled LES formulation was used in the cavity section to resolve the highly complex flow-acoustic resonant fields. The ZLES results were well validated by the experimental results in the literature in terms of the frequency, amplitude, and spatial features of the acoustic pressure pulsations. Subsequently, the spinning behavior and mechanism of the excited diametral acoustic modes and the resonant vortex-shedding modes were comprehensively illustrated. The results showed that the excited diametral acoustic mode span anticlockwise along the cavity circumference, resulting in intense acoustic-pressure fluctuations several times greater than at the inlet dynamic-pressure head, together with longitudinal pressure propagations. Using proper orthogonal decomposition analysis, the spinning mechanism was found to be closely related to the interaction between the α-mode and the β-mode, which had fixed temporal and spatial phase lags. Thereafter, the first vortex-shedding mode gave rise to a strong spinning motion of the resonant flow field, while the second vortex-shedding mode created a slight spinning motion. The corresponding phase-dependent flow fields at consecutive planes along the cavity circumference revealed the spatiotemporal evolution of the velocity variations, surface streamlines, and vorticity variations of the shedding vortices. Large-scale helical vortex tubes were formed within the cavity volume due to the strong spinning behavior.

Effect of nozzle pressure ratio on pulsation frequency of air jets used in hole drilling

In this study, air-jet experiments were performed to investigate the effects of nozzle pressure ratios (n) on the pulsation frequency and structure of free-flow and impinging-flow fields. The experiments performed for different nozzle pressure ratios involved the collection of a series of photographs of the free-flow field structure and the measurement of the pressure distribution and pulsation frequency of the impinging-flow field. In addition, the gray values of the photographs of the free-flow field were extracted to calculate the frequency spectrum of the free-flow field. When n > 1, the free-flow field oscillated spatially along the jet axial direction, but its frequency was independent of the spatial position and depended only on the nozzle pressure ratio. With an increase in the nozzle pressure ratio, the frequency values sequentially increased, decreased, increased, and then stabilized. The pressure of the impinging-flow field depended only on the stand-off distance, and decreased rapidly with increasing stand-off distance. However, the pressure distribution of the impinging-flow field was dependent on the nozzle pressure ratios, and with an increasing nozzle pressure ratio, the pressure distribution changed from radial attenuation along the jet direction to a distribution with multiple pressure peaks in the flow field. Multiple frequencies existed in the impinging-flow field, and the overall pulsation was stronger than that of the free-flow field for the same pressure ratios.

Dynamic characteristics of a hydro‐turbine governing system considering draft tube pressure pulsation

Hydropower takes on many tasks such as peak regulation and frequency modulation in the power system. In the actual operation process of the hydro-turbine governing system, there is a certain degree of pressure pulsation in the draft tube. When the system is under unrated operating conditions, the draft tube pressure pulsation is more intense, and its dynamic behaviour becomes more complicated. In this study, the draft tube pressure pulsation is introduced into the dynamic model of the hydro-turbine governing system, and its influences on the transient characteristics of the system are analysed under unrated conditions and rated conditions. The authors find that compared with the rated conditions, the draft tube pressure pulsation under unrated conditions has more significant effects on the transient characteristics of the system. A damped frequency of pressure pulsation is proposed in this study which provides an efficient method of regulating the dynamic behaviour of the system in real operation. All these findings are expected to be helpful for further study of the influence of pressure pulsation on transient characteristics of hydropower systems and improving their dynamic characteristics under operating conditions.

Study on hydraulic characteristics of large vertical axial-flow pump used as constant frequency power generation

In order to study the stability of power generation in reverse of a pumping station unit, the computational fluid dynamics simulation and finite element analysis of the whole passage has been carried out, to study the pressure pulsation and stress distribution law under the condition of power generation in reverse, and compared with them in pump mode. The simulation results showed that, under the condition of power generation in reverse, the pressure pulsation of each monitoring point in front and at back of the runner were higher than that under pump mode. The most amplitude of pressure pulsation was about twice as large as the pump mode, increased gradually from hub to rim. The flow was seriously affected by the rotating runner. The internal frequency of pressure pulsation was blade frequency. The results of fluid–solid coupling showed that the stress mainly concentrated on the root of the pressure side and the suction side of the blade, and the maximum equal stress appeared on the suction side of the blade. The maximum stress and strain value under the condition of power generation in reverse were 20% higher than that under pump mode, and the maximum stress was about twice.