Bidirectional Pumping Research Articles

Numerical Analysis of Unsteady Internal Flow Characteristics in a Bidirectional Axial Flow Pump

A bidirectional axial flow pump that utilizes an S-shaped hydrofoil design exhibits low efficiency and hydraulic instability when operated in reverse. In order to understand the unsteady flow characteristics of this bidirectional axial pump under different operating conditions, the SST k–ω turbulence model was applied to carry out a three-dimensional unsteady numerical simulation of the full flow channel of the pump. The reliability of the numerical calculation model was verified by comparing it with the experimental head and efficiency. The pressure pulsation characteristics on the impeller surface and the pump device under different operating conditions and the transient forces on the impeller were analyzed. The results show that the head and efficiency in reverse operation were lower than in forward operation and the flow streamline of the impeller outlet area was more turbulent in the reverse operation condition. The monitoring points at the inlet and the top of the impeller surface showed the largest pressure pulsation amplitude. The radial and axial forces on the impeller in the reverse operation were greater than those in the forward operation. Under a reverse 1.0 Qdes condition, the average pressure pulsation amplitudes at the inlet of the impeller were 19.2 times and 5.7 times of that at the inlet of the guide vane and the outlet of the impeller, respectively. This study provides a reference for the hydraulic design and optimization of bidirectional axial flow pumps.

Comparative experimental study on gain clamping performance of O-band BDFA with different pump schemes at different input powers

Gain clamping can overcome the effects of power transients caused by unstable factors when fiber amplifiers are used in optical networks. In recent years, bismuth-doped fiber amplifiers (BDFA) operating in the O-band have been developed rapidly, while there are fewer studies on its gain-clamping aspects. In this work, we experimentally investigate the gain-clamping performance of O-band BDFA with different pumping schemes in the ultra-wide input range. Variable optical attenuator (VOA), 3-dB coupler, and a Fiber Bragg Grating (FBG) are utilized to form a ring cavity to generate the oscillating light. The experimental results demonstrate that the BDFA achieves a gain stabilization range under all three pumping schemes compared to the unclamped one, with the best effect under bidirectional pumping. Under the condition that the pump power is 500 mW and the VOA loss is 0 dB, the maximum gain fluctuation (MGF) of the signal in the input range from −15 dBm to 6 dBm is less than 0.5 dB and the average output gain is 6.3 dB, while when the VOA loss is 5 dB, the MGF of the signal below 0 dBm is less than 0.36 dB and the average output gain is 10.3 dB. This work provides a positive reference value for the application of O-band BDFA in optical network systems.

1.2 W single-frequency Tm3+/Ho3+ co-doped fiber oscillator at 2050 nm.

In this Letter, a watt-level single-frequency fiber oscillator at 2050 nm was demonstrated for the first time, to the best of our knowlegde, in a linear laser cavity with a piece of an un-pumped Tm3+/Ho3+ co-doped fiber serving as a saturable absorber. With delicate optimization of mode filtering effect of the dynamic gratings formed in the saturable absorber, a maximum single-frequency laser output power of 1.2 W was achieved under a total bidirectional pump power of 5.8 W at 1570 nm, and the corresponding optical efficiency is 20.7%. This is, to the best of our knowledge, the highest power of a single-frequency fiber oscillator at the wavelength above 2 µm.

3.38 kW all-fiberized narrow linewidth fiber laser based on active polarization control using RMS-Prop algorithm

Active polarization control in high power narrow linewidth non-polarization maintained (non-PM) fiber amplifier is investigated in this paper. The non-PM fiber laser is realized employing bidirectional pump configuration seeded with narrow linewidth laser source. Root-Mean-Square propagation (RMS-prop) algorithm is developed and first employed in polarization control technique. When control system does not work, the polarization extinction ratio (PER) of output signal laser varies between 0.25 dB and 4.61 dB. When control system works, the PER stably remains above 12.2 dB during power amplification. At laser power of 3.38 kW, the PER is 12.2 dB, 3 dB linewidth is measured to be ∼0.32 nm, and beam quality (M2 factor) is M2x = 1.39, M2y = 1.50. This is the first time to realize over 3 kW linearly polarized fiber laser based on active polarization control to the best of our knowledge.

Investigation of gain-filtering Yb-doped fibers with different gain-dopant doping ratios for high power amplifier

We presented an investigation on gain-filtering Yb-doped fiber for the mitigation of transverse mode instability (TMI). The gain-filtering Yb-doped fibers were fabricated by modified chemical vapor deposition (MCVD) combined with solution doping technique. Four gain-dopant diameter ratio fibers, entailing 100% doping, ∼73% doping, Gaussian doping, and ∼57% doping, presented similar parameters with the core/inner cladding diameter of ∼30/400 μm and core numerical aperture (NA) of ∼0.061. The laser performances of four fibers were demonstrated by a bidirectional pumping all-fiber amplifier. The TMI thresholds of 100%-doped, ∼73%-doped, Gaussian-doped, and ∼57%-doped fibers, were measured to be ∼1753 W, ∼3089 W, ∼3048 W, and over 3301 W, corresponding to the M2 factors of ∼1.52, ∼1.40, ∼1.45, and ∼1.32, respectively. The experimental results indicated that by reasonably tailoring the gain-dopant doping diameter, better gain-filtering effect was manifested, exactly as higher TMI threshold and more superior beam quality. This contribution could provide an effective approach for obtaining high-brightness Yb-doped fiber amplifiers based on gain-filtering effect.

Investigation of cavitation and flow characteristics of tip clearance of bidirectional axial flow pump with different clearances

With the increasing application of bidirectional axial pump, it is necessary to study the flow and cavitation characteristics of bidirectional pump. In this paper, the cavitation and flow characteristics of the tip clearance under different clearances and different cavitation numbers of the S-hydrofoil bidirectional axial flow pump were studied by combining experimental and numerical simulation methods under reverse operation conditions. The section of the bidirectional pump was experimentally studied by high-speed photography and pressure pulsation. Based on the method of RANS, the SST-CC turbulence model and ZGB cavitation model were used to simulate the clearance cavitation of the bidirectional pump, and the cavitation morphology, velocity distribution, clearance vortex structure and energy distribution of blade tip clearance were investigated. The study reveals the flow characteristics of the clearance flow field of the bidirectional pump, and provides reference for the design and operation of it.

Design Optimization of Valve Plate of a Bi-directional Axial Piston Pump for Electro Hydrostatic Actuation Systems

Design Optimization of Valve Plate of a Bi-directional Axial Piston Pump for Electro Hydrostatic Actuation Systems

Effects of pump parameters on the oil absorption characteristics of bidirectional involute internal gear pumps

The symmetrical oil suction and discharge chambers and the reversing rotation condition of bidirectional involute internal gear pumps result in low oil absorption capacity and flow pulsation due to cavitation. However, efforts to address these issues suffer from an incomplete understanding of the effects of oil properties, suction chamber volume, suction pressure, and rotational speed on the oil absorption capacity and cavitation characteristics of these pumps. The present work addresses this issue by conducting detailed computational fluid dynamics (CFD) simulations. The results of analysis demonstrate that the degree of cavitation caused by changes in the mass fraction of dissolved gas in the oil is positively correlated with flow pulsation, while the degree of cavitation caused by changes in the suction port size, suction pressure, and rotational speed is negatively correlated with flow pulsation. The degree of cavitation in the oil suction cavity initially increases as the mass fraction of dissolved gas in the oil increases, and then decreases. The rotational speed exhibits a critical value, where the oil absorption capacity increases with increasing rotational speed below the critical value, and decreases with increasing rotational speed above the critical value. The results of this research are expected to be of great significance for guiding improvements in the design of bidirectional involute internal gear pumps and the determination of critical working conditions.

Design and numerical study of a bidirectional acoustic microfluidic pump enabled by microcantilever arrays.

Microfluidics offers a versatile and promising platform for various applications in biomedical and other fields, boasting cost-effectiveness, rapid analysis time, and a compact equipment footprint. However, achieving controlled and versatile microfluidic motion within implantable devices presents a significant challenge. In this study, we propose a novel bidirectional micro-pump design that leverages two sharp-edge microcantilever arrays, driven by ultrasound, to enable selective flow direction by manipulating the ultrasound frequency. Through systematic numerical simulation, we demonstrate the feasibility of this design and further optimize its performance through comprehensive parametric analysis. This work provides valuable guidance for the practical development of sharp-edge-based acoustic micro-pumps, particularly for potential implantable applications such as controlled drug release and in vivo sampling for advanced diagnostics.

Experimental comparison study of the performance of reflector-based O-band BDFA under different pumping schemes

A bismuth-doped fiber amplifier (BDFA) operating in O-band with a double-pass structure in combination with a reflector is experimentally compared in detail under three pumping schemes. Different pump powers and signal input powers are used to investigate the effect on gain and noise figure (NF). The results show that not all wavelengths in the O-band but only wavelengths in the 60 nm range (1290 nm-1350 nm) can be improved with a double-pass, where the improvement is most prominent at 1320 nm; The gain improvement can only be obtained with a double-pass when the signal is input with low-power (approximately below −7 dBm). Among the three pumping schemes, the gain enhancement is most prominent with bidirectional pumping. A maximum gain of 31 dB was achieved at 1320 nm for −20 dBm input signal in double-pass with the pump power of 500 mW under bidirectional pumping scheme, which is an improvement of nearly 25.4% compared to single-pass. In addition, compared to forward and backward pumping also improved by 5.7% and 23.8%. This work demonstrates that the performance of O-band BDFAs can be effectively enhanced by reflectors, which have positive practical significance and reference value.

Demonstration of 3kW × 2 ports bidirectional output oscillating-amplifying integrated fiber laser employing chirped and tilted fiber Bragg gratings for co-SRS suppression.

Bidirectional output oscillating-amplifying integrated fiber laser (B-OAIFL) is a newly developed configuration with many advantages like compactness and good reliability. In this work, a B-OAIFL with a low time-stabilized threshold was constructed by employing a pair of side pump/signal combiner in the oscillating section, which demonstrates smooth temporal characteristics with no pulse detected by the photodetector at the output power level of only a few of tens Watts. We investigated the effect of side pumping on the Raman Stokes light and verified its contribution to mitigating the temporal-chaos-induced stimulated Raman scattering (SRS). The phenomenon of co-SRS caused by the mutual excitation of backward Stokes light from two amplifying sections under bidirectional pumping was first reported and studied. A pair of chirped and tilted fiber Bragg gratings (CTFBGs) were applied between the oscillating and amplifying sections to suppress the co-SRS, and the effect of the number of CTFBGs on the suppression of co-SRS was studied in detail experimentally. Finally, we successfully suppressed the co-SRS, and achieved a 3kW × 2 ports laser output, with a near-single-mode beam quality of M A 2∼1.3,M B 2∼1.4. In contrast, without the use of CTFBG, only a 2 kW-level output was obtained from each port, limited by co-SRS (with an SRS suppression ratio of less than 15 dB). The maximum output power of end A and end B is 3133 W and 3213 W, with the SRS suppression ratio of about 27.6 dB and 28.1 dB, respectively. No TMI features were observed under bidirectional pumping. The results demonstrate a significant potential for further power scaling based on this configuration. To the best of our knowledge, it is the highest output power achieved based on the B-OAIFL.

Pumping scheme for ultra-wideband WDM transmission using distributed Raman amplification

This paper describes the pumping schemes for ultra-wideband (UWB) WDM transmission using only distributed Raman amplification. By using numerical analysis based on the Gaussian noise model, we evaluate the amplification performances for all-Raman UWB-WDM transmission using higher-order pumping and/or forward pumping in addition to conventional 1st-order backward pumping. Moreover, we discuss the effect of forward Raman gain in 1st-order bidirectional pumping configuration, and clarify that the forward Raman gain should be carefully optimized taking account of both noise performance and nonlinear degradation.

Positive and Negative Performance Analysis of the Bi-Directional Full-Flow Pump with an “S” Shaped Airfoil

In this study, model tests and numerical simulations are conducted to study the bi-directional full-flow pump (BFFP). Firstly, the head, efficiency and shaft power of the BFFP are significantly higher in the positive operating condition than in the negative operating condition. When the unit operates in the positive direction, the clearance reflux flow rate, the flow uniformity and velocity-weighted average angle of the impeller inlet, and the intensity of pressure pulsation are significantly greater than those during the negative operation. When the pump unit is operating at low flow rates, the clearance reflux produces a significant disturbance to the impeller inlet main flow. Two vortices appear in the near-wall area of the clearance outlet (i.e., impeller inlet), and the range of vortices is larger in the positive operation than in the negative operation. Secondly, at low-flow and design-flow conditions, the total entropy production of the pump unit in the positive direction is greater than that in the negative direction. When at small- and design-flow rates, the amplitude of pressure pulsation in the positive direction is smaller than that in the negative direction. This study will contribute to the research and development of a full-flow pump.

Comparison of transient characteristics of positive and negative power-off transition process of “S” shaped bi-directional full-flow pump

In this study, the positive and negative power-off process of a bi-directional full-flow pump is investigated by model tests and numerical simulations, and the results show that under steady conditions, the head of the bi-directional full-flow pump in the positive direction is larger than in the negative direction. The positive power-off process of the bi-directional full-flow pump is slower than the negative power-off process. The clearance backflow rate of the bi-directional full-flow pump continues to drop during the power-off process until it remains stable under the runaway condition. The clearance backflow causes the vortex at the impeller inlet and the size of the vortex gradually decreases during the power-off process. Compared to the positive power-off process, the backflow vortex ratio is greater, and therefore, the flow pattern is poorer during the negative power-off process. The entropy production rate in the negative power-off process is significantly greater than that in the positive power-off process. The pumping condition has the largest hydraulic loss in the whole power-off process. The runaway rotational speed in the positive power-off process is higher than that in the negative power-off process, and the axial force in the positive runaway condition is 1.40 times greater than in the negative runaway condition. During the power-off process, the vibration and pressure pulsation in the negative operation is significantly greater than that in the positive operation, and the acceleration of the impeller vibration from large to small is the Y (vertical) direction, Z (axial) direction, and X (horizontal) direction. The research in this paper can provide an important reference for the design and operation of the bi-directional full-flow pump.

Bidirectional Cladding-Pumped Multicore EDFA and its Optimization for Energy Efficiency by Tuning Pump Condition

This work investigates the feasibility of improving the energy efficiency of a cladding-pumped multicore (MC) EDFA by utilizing bidirectional (BD) pumping. We combined a conventional forward-cladding-pumped MC-EDFA with backward cladding pumping and tuned the pump-gain characteristics and gain shape by controlling the optical pump power ratio of its forward and backward pumps. Since EDFAs have wavelength dependence, output power equalization by each wavelength channel is extremely important for amplifying the wavelength division multiplexing (WDM) signal. The standard method of current equalization is to adjust the attenuation by the output power of each wavelength channel. The main issue with the current standard equalization is the indispensable optical power loss caused the reduced optical amplification efficiency of the EDFA. Our previous work demonstrated that the optical power loss due to equalization can be reduced by controlling the optical power ratio of the forward and backward pumps. This leads to improved energy efficiency of the signal amplification and equalization of both the WDM and spatial division multiplexing (SDM). <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this paper, we report our detailed investigation into the tuning amplification characteristics of the BD-MC-EDFA. Our main focus was the gain, noise figure (NF), and gain shape of a 7-core BD-MC-EDFA prototype when forward and backward optical pump power was changed. Under 8 W of total optical pump power, the percentage of 60% forward cladding optical pump power was found to be optimal for efficiency considering the minimum output optical power loss due to equalization. This condition translates into a 1.7% pump conversion efficiency (PCE) improvement, which corresponds to a 24% reduction of the total optical pump power compared to conventional MC-EDFA with only forward cladding pumping. Although the NF deteriorated by 1.0 dB in wavelength average in the 4.5-THz signal bandwidth in exchange for the efficiency improvement, degradation of the 34.2-GBaud polarization multiplexed 16 quadrature amplitude modulation (PM-16QAM) signal amplified by the BD-MC-EDFA operated under the optimized condition was negligible.

Quasi-Soliton Mode in a Multi-Span Fiber-Optic Communication System Using Optical Amplifiers

The paper considers a method for maintaining a quasi-soliton mode in a multi-span fiber-optic communication system using discrete Erbium optical amplifiers, as well as Raman amplifiers with distributed amplification with counter and bidirectional pumping. The OptiSystem 19 and OptiPerformer 19 programs were used to model quasi-soliton fiber-optic communication systems. The simulation results are compared with theoretical data, and the advantages of a fiber-optic communication system with a Raman amplifier and bidirectional pumping are demonstrated.

190km Φ-OTDR with bidirectional Raman and relay erbium-doped fiber hybrid amplification

In this paper, a long-distance coherent detection phase-sensitive optical time-domain reflectometer (Φ-OTDR) scheme with bidirectional Raman and relay erbium-doped fiber hybrid amplification is proposed. The bidirectional Raman pump light acting on the erbium-doped fiber (EDF) can realize the passive amplification of pulsed signal light and Rayleigh backward scattering (RBS) light at the same time. The scheme utilizes bidirectional 1455 nm pumps as the pump source of relay amplification to achieve a longer sensing distance. Experimental results demonstrate that, an ultra-long Φ-OTDR system with 190 km sensing distance and 22 m spatial resolution is realized. Multi-point vibration signals are located and restored at 69.67 km, 120.13 km and 190.79 km, respectively. The average signal-to-noise ratio (SNR) of positioning curve is 10.32 dB, the average SNR of demodulated phase signal is 26.02 dB, and the frequency response range is from 5 Hz to 150 Hz. Furthermore, the sensing system has good linear characteristics of phase demodulation with a correlation coefficient of 0.997. The actual disturbance events are also detected at the far-end of sensing fiber. To the best of our knowledge, this system achieves the longest-distance Φ-OTDR without relay power supply. This passive hybrid amplification method can avoid the intermediate power supply along sensing fiber, which provides a reference for long-distance vibration monitoring of Φ-OTDR system.

A new approach to controlling a hydraulic indirect elevator with a variable-speed pump

The paper describes a new approach to the issue of controlling an indirect elevator with a bidirectional variable-speed pump and a simple controller based on the position sensor. The aim of this paper is to present a method of controlling the speed of the elevator to ensure smooth movement and proper positioning of the car on the floor, regardless of its load and ropes rigidity. The main feature of the proposed solution is the use of a frequency inverter in vector mode to control the speed of the car in both directions. The control function is based on virtual cams comparing actual measurements from the car position sensor. The proposed control strategy has been experimentally verified on the existing indirect elevator drive, and the obtained results indicate a very high accuracy in maintaining and shaping the speed and positioning of the car. The conducted research confirms the possibility of using a new method of controlling hydraulic and indirect elevators. The benefits of this method include a less complex hydraulic system, the control of overloads in the car and vibrations in the rope system, and the possibility of energy recovery.

Influence of central wavelength of pump source and pump direction on transverse mode instability threshold of fiber laser

In high-power ytterbium ion-doped fiber lasers where the output power is limited only by the transverse mode instability (TMI), the TMI threshold of fiber lasers with counter-propagating pumping (counter-pumping) structure is usually greater than that of co-propagating pumping (co-pumping), and bidirectional pumping (bi-pumping) is in turn greater than that of counter-pumping. In order to increase the TMI threshold, we optimized the central wavelength of the pump source to a bi-pumped fiber laser oscillator. In the experiment, we found that only the central wavelength of the pump source is changed in the same fiber laser, and the TMI threshold of the bi-pumping structure is sometimes greater than the sum of the TMI thresholds at the time of only co-pumping and only counter-pumping, sometimes approximately equal to, sometimes less. In addition, an interesting phenomenon was also reported that the counter-pump injection power of the fiber laser in the TMI threshold of bi-pumping is larger than the TMI threshold of only counter-pumping. Using the fiber laser simulation software, we explained the above phenomenon from the two directions of thermal effect and population reverse ratio in the active fiber. These research results are helpful to further optimize each device parameter of fiber laser and achieve higher power output.

Design of a 5th Generation District Heating Substation Prototype for a Real Case Study

The evolution of district heating networks is moving toward low temperatures in heat distribution with so called 4th generation networks. However, the lowest heat transfer fluid temperatures in district heating are achieved through ultra-low temperature networks, referred to as 5th generation district heating networks (5GDHNs). Low temperatures in heat distribution results in an extremely different configuration of 5GDHN compared to traditional district heating network, especially in the grid substation due to the inability to directly couple the grid with the buildings. This paper presents a detailed design of a 5th generation substation prototype, which is carried out to verify the proper operation and monitor the performance of this type of substation in a real case study. The prototype is fed by low-temperature waste heat, currently dissipated through evaporative towers, and will be built in the city of Brescia, Italy. The layout of the substation prototype, consisting of a bidirectional pumping system, a reversible water-to-water heat pump, an inertial thermal energy storage and a heat exchanger, is presented. An analysis is performed to figure out which refrigerant offers the best performance of the heat pump. In addition, fixed the refrigerant, the performance of the grid connected heat pump is found to be increased from 29.5% to 55.5% for both heating and cooling compared with a stand-alone air-to-water heat pump solution. Finally, the process flow diagram and the piping and instrumentation diagram of the substation are presented and commented.