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Abstract A large capacity and high-pressure piston wa-ter pump is often used as the power supply in a high-pressure water-jet propulsion system (HWPS). When thepiston water pump works, some flow and pressure pulsationis generated and then creates large thrust pulsation and jetnoise. In most cases, an accumulator charged constantpressure gas is always installed near the outlet of the waterpump to absorb the flow and pressure pulsation. If thethrust of HWPS is required to alter, the rotation and outputpressure of the water pump will change. So, the function ofthe accumulator absorbing flow pulsation and pressurepulsation will weaken. 35981
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To solve this problem, an effectivemeans that makes multiple accumulators which are chargeddifferent pressures to connect with the outlet chamber ofthe water pump is put forward in this paper. According tothe structural pattern of water pump, working pressurerange of HWPS and allowable value of pressure pulsationfactor, some key parameters, could be worked out by op-timal calculation method proposed first, such as the numberof accumulators, volume and charged pressure of eachaccumulator. Finally, results of simulation and experimentrevealed that three pairs of accumulators, whose pa-rameters were optimally calculated from actual workingconditions, could keep the pressure pulsation factor toabout the allowable value all along when working pressureof HWPS varied over the range. Keywords Flow pulsation Pressure pulsation Accumulator Water pump High-pressure water-jetpropulsion systemList of symbolsAA Cross-sectional area of the anterior pipeline ofaccumulator (m2)AN Passage area of nozzle (m2)Cd Flowrate coefficient of the anterior pipeline ofaccumulatorCN Flowrate coefficient of nozzleCd Flowrate pulsation coefficientdA Inner diameter of the anterior pipeline ofaccumulator (m)fq Frequency of the flow pulsation (Hz)fp Frequency of the pressure pulsation (Hz)K Specific heat ratio, K = 1.4lA Length of the anterior pipeline of accumulator (m)n Rotation speed of water pump (r/min)N Number of pressure spotsP Working pressure of HWPS, namely outletpressure of water pump (Pa)pAk Gas pressure in the kth accumulator (Pa)pAqk Initial charged pressure in the kth accumulator(Pa)pci The ith pressure spot calculated (Pa)pmax Maximum working pressure of water pump (Pa)pmin Minimum working pressure of water pump (Pa)pN Outlet pressure of nozzle (Pa)pdmax Maximum value of pressure pulsation (Pa)pdmin Minimum value of pressure pulsation (Pa)pdmax(m) Crest values of pressure pulsation (Pa)pdmin(m) Trough values of pressure pulsation (Pa)q Instantaneous output flowrate of water pump(m3/s) qAk Flowrate of the kth accumulator (m3/s)qN Flowrate through nozzle (m3/s)qr Delivery capacity of water pump (m3/r)R The number of pressure spots to calculate thepdmax and pdmin of pressure pulsationRek Reynolds number in anterior pipeline of the kthaccumulatorvk Water velocity in anterior pipeline of the kthaccumulator (m/s)VAk Volume of the kth accumulator (m3)VAqk Bladder volume of the kth accumulator (m3)VAr Net volume of accumulators (m3)zp Piston number of water pumpdp Pressure pulsations factor[dp] Allowable value of pressure pulsations factordVm1 Pulsation volume of water pump (m3)Dpk Pressure difference of the anterior pipeline ofthe kth accumulator (Pa)kk Resistance coefficient along anterior pipeline ofthe kth accumulator’s inletl Kinematic viscosity of water (m2/s)q Density of water (kg/m3)1 IntroductionThe high-pressure water-jet propulsion system (HWPS),which is a novel thruster, ejects a high-speed and high-pressure water stream from a nozzle to engender thrust andpushes watercraft forward [1].
Usually, a special axial pistonwater pump is employed as a power supply in HWPS. Theswash plate angle of this axial piston water pump is 25 ,which is larger than other piston pumps (about 10 ), so thewater pump has a large displacement. Besides, the wa-ter pump can discharge high-pressure water. Therefore, thewater pump can generate large thrust. When the axial pistonwater pump is working, each piston discharges water dis-continuously. So the water pump’s instantaneous flow,whichis related to the revolution speed and the number of piston,has a periodic change, namely flow pulsation. The basicfrequency fq of the flow pulsation is closely related to therevolution speed n and piston number Zp of the water pump,that is fq = nZp/60 (Zp is even) or fq = nZp/30 (Zp is odd).When the flow pulsation comes across impedance (suchas orifices, elbows, pipes, etc.), some pressure pulsations areproduced. These pressure pulsations, which include a basicfrequency fp = fq and some harmonic frequency m 9 fp(m = 2, 3, 4…), could arouse some strong piping vibrationsand fluid noise as a vibration source. Because the thrust andjet noises are closely related to the output pressure of thewater pump in HWPS, the pressure pulsation can generatesome thrust pulsation and acutely jet noise. In such a case,an effective buffer technology is needed to restrain flowpulsation and pressure pulsation in HWPS.As for the flow pulsation and pressure pulsation phe-nomenon of piston hydraulic pump, researchers have car-ried out some good methods to reduce it. Among thesemethods, the most effective and widely used method is toinstall some bladder type accumulators near the outlet of ahydraulic pump, so as to absorb the flow pulsation and putdown the pressure pulsation [2–5]. To a bladder type ac-cumulator, the bladder volume and charged pressure are thetwo most important structural parameters, which are diffi-cult to be changed when working. Thus, the optimumvalues of the two parameters should be determined ac-cording to the structure parameters, output flowrate andpressure of the hydraulic pump, so as to maximize theefficiency of absorbing flow and pressure pulsation [6–8].However, the thrust of HWPS could be changed only byshifting the rotation speed of the water pump to adjust theoutlet flowrate and pressure.