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The concept of bound states in the continuum and leaky resonances is utilized in the design of a reactive silencer that can effectively suppress significant spectral lines while maintaining a low-pressure drop within the flow duct and does not require additional installation space. By adjusting the geometrical parameters of thin plates that are embedded in a waveguide, quasi-bound states (or leaky resonances) can be achieved. An optimization algorithm is employed to fine-tune these parameters, and this process is illustrated through two specific examples. The resulting design is validated through numerical simulations that account for the effects of low Mach number flow. The investigations showed that it is possible to design a spectral silencer with low-pressure drop based on the chosen approach. By combining several leaky resonances, stopbands were created with a transmission loss of up to 17 dB in a frequency range of 10 Hz. [ABSTRACT FROM AUTHOR]

Aerodynamic and aeroacoustic performance experiments were carried out on four- and eight bladed, 1.542 m diameter, axial flow cooling fans, with constant solidity and hub-to-tip ratio. Tests were conducted in an ISO5801, Type A Fan Test facility. The tip gap (TG) was reduced from 4 mm (0.26% fan diameter) to 2 mm (0.13% fan diameter), to 0 mm, for both fan configurations. The noise profile of each fan configuration at the same TG over the whole volumetric flow rate spectrum was compared to each other. The 4 mm (0.26%) TG is used as a baseline to measure the nett increase or decrease in sound levels. Noise emissions decreased as the TG was reduced. It is discovered that the four bladed fan configuration had lower noise emissions than the eight bladed fan configuration at all blade tip clearances at design flow rate. It is concluded that reducing the TG and number of blades, at constant solidity, reduces sound emissions. The 0 mm TG for the four bladed fan produced the greatest reduction in noise emissions. An increase in fan total-to-static performance is observed when reducing the TG for both fan configurations. [ABSTRACT FROM AUTHOR]

The flow in the vane-less diffuser bend and return the channel of radial turbo-machines which is perturbed by the time-periodic and circumferentially passing jet-wake structure exited from the upstream impeller, and the transient characteristics of separation and fluctuation occurring in these stationary components determine the operational stability and performances of the turbo-machines especially for the next stage. In this work, we present a numerical investigation on the transient separation and fluctuation behaviors of turbulent flow in a sector of a 180° bended axisymmetric U-turn channel subjected to time-periodic gust inflow which passes in the circumferential direction. The objective is to explore the effect of period of gust inflow, in simulating the non-dimensional blade passing frequency (BPF*) in turbo-machines, on the characteristics of flow in the whole U-turn channel. Numerical results reveal that flow separation occurs in the curved section for about half the cycle at BPF* = 1 and 2, and earlier separation is observed for BPF* = 2, while there is no separation for BPF* = 5 and 10. There is a phase lag between the local skin friction coefficient in the channel and gust inflow, and the magnitude of the phase lag is related to BPF*. As BPF* increases, the thickness of the boundary layer on both walls decreases. [ABSTRACT FROM AUTHOR]

Advances in wind-plant control have often focused on more effectively balancing power between neighboring turbines. Wake steering is one such method that provides control-based improvements in a quasi-static way, but this does little to fundamentally change the wake recovery process, and thus, it has limited potential. This study investigates use of another control paradigm known as dynamic wake control (DWC) to excite the mutual inductance instability between adjacent tip-vortex structures, thereby accelerating the breakdown of the structures. The current work carries this approach beyond the hypothetical by applying the excitation via turbine control vectors that already exist on all modern wind turbines: blade pitch and rotor speed control. The investigation leverages a free-vortex wake method (FVWM) that allows a thorough exploration of relevant frequencies and amplitudes of harmonic forcing for each control vector (as well as the phase difference between the vectors for a tandem configuration) while still capturing the essential tip-vortex dynamics. The FVWM output feeds into a Fourier stability analysis working to pinpoint candidate DWC strategies suggesting fastest wake recovery. Near-wake length reductions of >80% are demonstrated, although without considering inflow turbulence. Analysis is provided to interpret these predictions considering the presence of turbulence in a real atmospheric inflow. [ABSTRACT FROM AUTHOR]

Being able to predict ship and marine propulsion noise is an important issue for naval architectures and the international maritime community. The main objective of this paper is the numerical investigation on the noise propagation by the high skew marine propeller working in a non-uniform inflow via RANS solver in the broadband frequency range. The pressure fluctuations were monitored at three points on the propeller blade, then by using the FFT operator we computed the blade passing frequency (BPF) for different propeller loading conditions. Based on these pressure pulses and adopting the Fowcs Williams-Hawking model we calculated noise radiated at the monitoring points. The results showed the BPF and noise level increased by increasing the load on the blades and we also observed that the noise generated at the leading edge was greater than at other points. Furthermore, the study of pressure fluctuations showed the propeller tip has more pressure variations in one revolution than other regions of the propeller surface.

This paper presents efficient procedures to model multistage flows using Fourier-based methods. The Favre-averaged nonlinear harmonic method is extended to compute multistage flows by introducing rotor-rotor or stator-stator interactions. A unified treatment to transfer disturbances through blade-row interfaces is also formulated. The performance of the proposed method is demonstrated in a multistage compressor and turbine with different levels of flow nonlinearity. The computed solutions using the proposed method matches well with unsteady Reynolds-averaged Navier-Stokes (RANS) simulations but require far smaller computational resources. A method is proposed to reduce the computational cost of clocking studies even further by building reduced models from existing Fourier modes. The method allows the flowfield for a required clocking position to be constructed by postprocessing the Fourier modes computed for a single arbitrary clocking configuration. This technique is demonstrated by predicting compressor efficiency variation with respect to rotor blade clocking and wall temperature distributions in a turbine hot streak migration problem. Excellent agreement with unsteady RANS simulations is found. The proposed methods become less accurate in the presence of large flow nonuniformity but the produced solutions still show significant improvement over mixing plane solutions. [ABSTRACT FROM AUTHOR]

Investigations and observations on fluid flow and performance characteristics (numerically and experimentally) and sound generation (experimentally) of single and double outlet squirrel cage fans are performed in this study. The main objective is to survey the performance of double outlet fans and the effect of two volute tongues as main sound sources. Fan performance and sound experiments are conducted using an in-duct experimental setup. The efficiency and pressure curves show that each outlet channels of the double outlet fan operates similar to a single outlet one. As a criterion for evaluating the sound generation, total sound pressure level (SPL) and the noise component at blade passing frequency (BPF) in the power spectrum are considered. A comparison between the total sound pressure levels of the fans shows that in both of them the BPF noise increases with flow rate, while higher SPL is found for the double outlet one. An exactly-higher velocity jet/wake flow from the rotor in double outlet fan is responsible for the higher BPF noise.

The demands to apply transonic centrifugal compressor have increased in the advanced gas turbine engines. Various techniques are used to increase the aerodynamic performance of the centrifugal compressor. The effects of the inclined leading edges in diffuser vanes of a transonic centrifugal compressor on the flow-field unsteadiness and noise generation are investigated by solving the compressible, three-dimensional, transient Navier–Stokes equations. Diffuser vanes with various inclination angles of the leading edge from shroud-to-hub and hub-to-shroud are numerically modeled. The results show that the hub-to-shroud inclined leading edge improves the compressor performance (2.6%), and the proper inclination angle is effective to increase the stall margin (3.88%). In addition, in this study, the transient pressure variations and radiated noise prediction at the design operating point of the compressor are emphasized. The influences of the inclined leading edges on the pressure waves were captured in time/space domain with different convective velocities. The pressure fluctuation spectra are calculated to investigate the tonal blade passing frequency (BPF) noise, and it is shown that the applied inclination angles in the diffuser blades are effective, not only to improve the aerodynamic performance and stall margin, but also to reduce the BPF noise (7.6 dB sound pressure level reduction). Moreover, it is found that the diffuser vanes with inclination angles could suppress the separation regions and eddy structures inside the passages of the diffuser, which results in reduction of the overall sound pressure level and the broadband noise radiated from the compressor. [ABSTRACT FROM AUTHOR]

Investigations and observations on fluid flow and performance characteristics (numerically and experimentally) and sound generation (experimentally) of single and double outlet squirrel cage fans are performed in this study. The main objective is to survey the performance of double outlet fans and the effect of two volute tongues as main sound sources. Fan performance and sound experiments are conducted using an in-duct experimental setup. The efficiency and pressure curves show that each outlet channels of the double outlet fan operates similar to a single outlet one. As a criterion for evaluating the sound generation, total sound pressure level (SPL) and the noise component at blade passing frequency (BPF) in the power spectrum are considered. A comparison between the total sound pressure levels of the fans shows that in both of them the BPF noise increases with flow rate, while higher SPL is found for the double outlet one. An exactlyhigher velocity jet/wake flow from the rotor in double outlet fan is responsible for the higher BPF noise. [ABSTRACT FROM AUTHOR]

Flow around the Guide vane! (GV) in Francis turbine differs with the shape of hydrofoils. The difference in the pressure of fluid travelling 10 pressure side and suction side of GV contributes to flow behavior. This study presents the numerical technique using alternative clearance gap method to predict the flow around GV and its consequent effect on turbine performance. GV profile has a significant effect on the performance of the turbine with sediment contained flui i flow. In this paper, symmetrical NACA 0012 and cambered NACA 2412, NACA 4412 hydrofoils are studied introducing 0 mm, 2 mm, and 4 mm clearance gaps. Vortex filament can be seen when fluid leaves the clearance gap due to the leakage flow occurring through the gap. The intensity of vortex leaving clearance gap rises with an increase in the size of the clearance gap. However, in the case of asymmetrical GV profile, the velocity of fluid travelling along the vortex compared to that of symmetrical hydrofoil is lower. In case of low specific speed Francis turbines, this vortex is found to be a major reason to erode the runner surface d ie to high velocity of a sand particle travelling with them. With the alternative clearance gap approach, this paper compares the pressure pulsation downstream o f GVs contributed by leakage flow for three NACA profiles, whose frequency is half of blade passing frequency. [ABSTRACT FROM AUTHOR]

Despite their high manufacturing cost and structural deficiencies especially in tip regions, highly skewed propellers are preferred in the marine industry, where underwater noise is a significant design criterion. However, hydrodynamic performances should also be considered before a decision to use these propellers is made. This study investigates the trade-off between hydrodynamic and hydroacoustic performances by comparing conventional and highly skewed Seiun Maru marine propellers for a noncavitating case. Many papers in the literature focus solely on hydroacoustic calculations for the open-water case. However, propulsive characteristics are significantly different when propeller-hull interactions take place. Changes in propulsion performance also reflect on the hydroacoustic performances of the propeller. In this study, propeller-hull interactions were considered to calculate the noise spectra. Rather than solving the full case, which is computationally demanding, an indirect approach was adopted; axial velocities from the nominal ship wake were introduced as the inlet condition of the numerical approach. A hybrid method based on the acoustic analogy was used in coupling computational fluid dynamics techniques with acoustic propagation methods, implementing the Ffowcs Williams-Hawkings (FW-H) equation. The hydrodynamic performances of both propellers were presented as a preliminary study. Propeller-hull interactions were included in calculations after observing good accordance between our results, experiments, and quasi-continuous method for the open-water case. With the use of the time-dependent flow field data of the propeller behind a non-uniform ship wake as an input, simulation results were used to solve the FW-H equation to extract acoustic pressure and sound pressure levels for several hydrophones located in the near field. Noise spectra results confirm that the highest values of the sound pressure levels are in the low-frequency range and the first harmonics calculated by the present method are in good accordance with the theoretical values. Results also show that a highly skewed propeller generates less noise even in noncavitating cases despite a small reduction in hydrodynamic efficiency. [ABSTRACT FROM AUTHOR]

A large-scale, vaned-voluted centrifugal pump can be applied as the key component in water-transfer projects. Pressure pulsation will be an important factor in affecting the operation stability. This paper researches the propagation and spatial distribution law of blade passing frequency (BPF) and its harmonics on the design condition by numerical simulation. Experimental and numerical monitoring is conducted for pressure pulsation on four discrete points in the vaneless region, which shows that the BPF is dominant. The pulsation tracking network (PTN) is applied to research propagation law and spatial distribution law. It provides a reference for frequency domain information and visualization vaned diffuser. The amplitude of BPF and its harmonics decays rapidly in the vaneless region. BPF and BPF’s harmonics influence each other. BPF has local enhancement in the vaneless region when its harmonics attenuate. In the vaned diffuser, the pulsation amplitude of BPF attenuates rapidly, but the local high-pressure pulsation amplitude can be found on the vane blade concave side because of obstruction and accumulation of the vaned diffuser. In the volute, the pulsation amplitude of BPF is low with the decelerating attenuation. This study provides an effective method for understanding the pressure pulsation law in turbomachinery and other engineering flow cases.

The demands to apply transonic centrifugal compressor have increased in the advanced gas turbine engines. Various techniques are used to increase the aerodynamic performance of the centrifugal compressor. The effects of the inclined leading edges in diffuser vanes of a transonic centrifugal compressor on the flow-field unsteadiness and noise generation are investigated by solving the compressible, three-dimensional, transient Navier–Stokes equations. Diffuser vanes with various inclination angles of the leading edge from shroud-to-hub and hub-to-shroud are numerically modeled. The results show that the hub-to-shroud inclined leading edge improves the compressor performance (2.6%), and the proper inclination angle is effective to increase the stall margin (3.88%). In addition, in this study, the transient pressure variations and radiated noise prediction at the design operating point of the compressor are emphasized. The influences of the inclined leading edges on the pressure waves were captured in time/space domain with different convective velocities. The pressure fluctuation spectra are calculated to investigate the tonal blade passing frequency (BPF) noise, and it is shown that the applied inclination angles in the diffuser blades are effective, not only to improve the aerodynamic performance and stall margin, but also to reduce the BPF noise (7.6 dB sound pressure level reduction). Moreover, it is found that the diffuser vanes with inclination angles could suppress the separation regions and eddy structures inside the passages of the diffuser, which results in reduction of the overall sound pressure level and the broadband noise radiated from the compressor.

The present study investigated the spectrum characteristics of unsteady disturbance and the tip leakage vortex evolution during pre-stall process for a contra-rotating axial compressor (CRAC). Transient numerical simulation was carried out in a single passage of the CRAC. The original transient fluctuation and oscillation of the tip leakage vortex structure with varying flow capacity of the CRAC were revealed using circle-like pattern figure and phase-locked root mean square (PLRMS). Additionally, the tip leakage flow in terms of vortex structure evolution was visualized for the sake of revealing the flow mechanism during pre-stall process. Results show that the unsteady fluctuation first appears at φ=0.3622, and the fluctuation frequency is 2.86 BPF. Unsteady disturbance source is mainly located at the tip side of the downstream rotor leading edge. From the choking point to the near stall condition, tip leakage vortex is always found in the tip leading edge of the upstream rotor. In addition, the tip leakage vortex of upstream rotor remains in the same place over time, i.e., no fluctuation, even when the downstream rotor entered into stall state. Such a phenomenon indicates that the stall point of the contra-rotating compressor is determined by the downstream rotor. Moreover, the maximum fluctuation position is mainly concentrated on the interface between the mainstream and the tip leakage vortex of the downstream rotor. By throttling the compressor, the angle between the main leakage vortex and the circumferential direction decreases gradually. When the main leakage vortex touches and continuously impacts on the leading edge of the adjacent blade, the unsteady disturbance, which is different from that of BPF, appears firstly. [ABSTRACT FROM AUTHOR]

Vertical axis wind turbines (VAWT) are a source of renewable energy and are used for both industrial and domestic purposes. The study of noise characteristics of a VAWT is an important performance parameter for the turbine. This study focuses on the development of a linear microphone array and measuring acoustic signals on a cambered five-bladed 45 W VAWT in an anechoic chamber at different tip speed ratios. The sound pressure level spectrum of VAWT shows that tonal noises such as blade passing frequencies dominate at lower frequencies whereas broadband noise corresponds to all audible ranges of frequencies. This study shows that the major portion of noise from the source is dominated by aerodynamic noises generated due to vortex generation and trailing edge serrations. The research also predicts that dynamic stall is evident in the lower Tip speed ratio (TSR) region making smaller TSR values unsuitable for a quiet VAWT. This paper compares the results of linear aeroacoustic array with a 128-MEMS acoustic camera with higher resolution. The study depicts a 3 dB margin between two systems at lower TSR values. The research approves the usage of the 8 mic linear array for small radius rotary machinery considering the results comparison with a NORSONIC camera and its resolution. These observations serve as a basis for noise reduction and blade optimization techniques.

• Application of Active noise control in a pump system with variable point of operations for the very first time. • Key technology for smart-grid controlled pump system in order to avoid undesirable pressure pulsation related issues like vibration and noise. Smart-grid control aims to use current power converter technology of pump drives for grid stabilization. Hereby, fluctuations of the power grid frequency are transmitted to the pump drive resulting in pump speed changes. Along with the inherent impeller design these pump speed changes are resulting in pressure pulsations which propagate as hydro acoustic pressure waves throughout the pump system causing noise and vibration issues in the piping system. Therefor, in order to realize smart-grid control, a solution must be found to attenuate or counteract these hydro acoustic pressure waves. In an earlier work [1] , an active noise control (ANC) system to reduce pressure pulsations at a pump's blade passing frequency (BPF) was published with the focus on constant points of operation. However, utilizing smart-grid control will results in high gradients of the pump speed and constantly changing points of operation are to be expected. This paper aims to attack those kinds of operating conditions. Within this paper, moving frequencies of interest at different pump speed gradient with and without active attenuation are analyzed and extracted from time series data by means of Vold-Kalman order tracking filter. In relation to possible fluctuations in the power grids frequency, the active attenuation performance of the ANC system is evaluated. [ABSTRACT FROM AUTHOR]

Pressure fluctuation is the primary factor that affects the stability of turbomachines. The goal of the present work is to explore the propagation of pressure fluctuations in a two-stage double-suction centrifugal pump. The pressure fluctuation characteristics of each component of a two-stage double-suction centrifugal pump are simulated under four typical flow rates based on the SST k-ω turbulence model. It is shown that the pressure fluctuation frequency at blade passing frequency and its first harmonic is the same at the suction chamber, the leading edge, and the middle of the first-stage impeller, which is different from the rotor–stator interaction. Moreover, the uneven impeller inlet flow distribution will produce fluctuations with rotation frequency and its harmonics at the leading edge of the impellers in both stages. Finally, broadband frequency is found at the trailing edge of the impellers in both stages associated with the first harmonic of the rotation frequency, especially under the part load condition. The large size backflow vortex appears in the blade flow channel leading to the low-pressure zone between the impeller, the tongue, and the start of the partition. That is why the pressure drops significantly twice in one rotation period when the blades pass through the tongue and the start of the partition.

Three-dimensional, compressible, unsteady Navier–Stokes equations are solved to investigate the flow field of a transonic centrifugal compressor with high compression ratio. The computational domain is consisted of an inlet bell mouth and an impeller with splitter blades, followed by a two-dimensional wedge vaned diffuser. The numerical method was validated by comparing the results with those of experiments in terms of aerodynamic compressor performance and flow field within the compressor passages. A detailed analysis of instantaneous and time-averaged flow field was conducted in the impeller and diffuser passages. The present study focuses on the pressure fluctuations and entropy production within the impeller and diffuser passages at the compressor design point. It is shown that the interaction between the impeller and diffuser blades leads to unsteadiness at the interface region and a pulsating behavior within the diffuser passages. Pressure waves with different convective velocities, generated by the impeller–diffuser interaction and pseudo-periodic unsteady separation bubbles, are captured in the time/space domain along the diffuser blade surfaces. The pressure fluctuation spectra were evaluated to analyze the noise characteristics of the centrifugal compressor as the main source of blade passing frequency noise. It is expected that the current unsteady Reynolds-Averaged Navier–Stokes (URANS) approach can be used as a tool for the prediction of unsteady flow and compressor noise characteristics with a proper turbulence model and well-resolved grids. [ABSTRACT FROM AUTHOR]

Three-dimensional, unsteady Navier-Stokes equations are numerically solved to investigate the turbulent flows in a stirred vessel. The computational domain consists of an unbaffled, cylindrical vessel with a pitched-blade turbine impeller. An Eulerian-Eulerian multiphase flow model is applied to determine the shape of the free-surface vortex core. This numerical method is validated by comparing its results with laser Doppler velocimetry measurements in terms of velocity distribution and turbulence kinetic energy profiles at different positions. In the present study, URANS approach with a hybrid zonal turbulence model, k − ω SST and SST-SAS, is used to predict the unsteady pressure and velocity fluctuations within the vessel. Pressure and inward-outward radial velocity waves are generated by the impeller rotation and are captured in the time/space domain close to the impeller trailing edge. The pressure and velocity spectra are computed to characterize the blade passing frequency as the main source of unsteadiness in the turbulent flow within the vessel. The results indicate that the current URANS approach with a proper turbulence model and well-resolved grids can be used as a predictive tool for the flow field and large turbulence scales in the stirred tanks. [ABSTRACT FROM AUTHOR]

Cavitation in pumps causes destructive consequences and occurs at certain operating circumstances. Therefore, it must be detected and prevented. The main thrust of the present work is detection and investigation of cavitation in a centrifugal pump experimentally, by monitoring the flow characteristics as well as the vibration spectrum. It is an attempt to declare the discrete signature of cavitation at various strengths on the vibration spectrum. The experimental results on a centrifugal pump at a rotational speed of 2850 rpm and absolute values of suction pressures from 10 to 78 kPa, showed that the inception of cavitation is declared by sudden deterioration in the hydraulic characteristics, decrease in the efficiency and increase in the overall vibration level. As the cavitation strength increases, the vibration level decreases and then increases sharply. Cavitation can be detected by online monitoring of the vibration amplitude of the discrete frequencies corresponding to the pump rotational speed and the first blade passing. As the pump operation moves from no-cavitation to cavitation case, the vibration amplitude of the rotational speed frequency increases while it decreases for the first passing frequency. Also, the cavitation in pumps signs the vibration spectrum by appearance of high energy at high frequencies. [ABSTRACT FROM PUBLISHER]

This paper presents an elucidation of three-dimensional flow phenomena that induce an aero-acoustic sound of Blade passing frequency (BPF). Three-dimensional separated and vortical flow fields in an air conditioning system have been investigated by Experimental fluid dynamics (EFD) analysis using an unsteady wall pressure measurement system and by Computational fluid dynamics (CFD) analysis using a Reynolds-averaged Navier-Stokes (RANS) simulation as described in the first report of the present study. Generally, the aero-acoustic sound of BPF is one of the main aero-acoustic sounds in air conditioning systems. Based on the EFD analysis, the wall pressure fluctuation of BPF is found to be not only located near the scroll tongue region but also widely located around the scroll casing wall. It was found that there is no correlation between the sensor positions in the circumferential direction and the pressure fluctuation level of BPF. Based on the CFD analysis results, it was found that an attachment line on the center of the scroll casing wall develops by interacting with secondary flow from the multi-blade fan. A pair of secondary vortex structures in the scroll casing longitudinally develops in the circumferential direction. As the pair of secondary flow structures with high vorticity develops in the circumferential direction and interacts with the scroll casing, wall pressure fluctuation of BPF is generated even though it is located far away from the scroll tongue. [ABSTRACT FROM AUTHOR]

Current approaches to fan noise simulation are mainly based on the Lighthill equation and socalled aeroacoustic analogy, which are also based on the transformed Lighthill equation, such as the wellknown FW-H equation or the Kirchhoff theorem. A disadvantage of such methods leading to significant modeling errors is associated with incorrect solution of the decomposition problem, i.e., separation of acoustic and vortex (pseudosound) modes in the area of the oscillation source. In this paper, we propose a method for tonal noise simulation based on the mesh solution of the Helmholtz equation for the Fourier transform of pressure perturbation with boundary conditions in the form of the complex impedance. A noise source is placed on the surface surrounding each fan rotor. The acoustic fan power is determined by the acoustic-vortex method, which ensures more accurate decomposition and determination of the pressure pulsation amplitudes in the near field of the fan. [ABSTRACT FROM AUTHOR]

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A series o f continuous vibration measurements in 14 upwind wind turbines o f the same model and belonging to the same wind farm have been conducted. The data were acquired over a period lasting approximately half a year. The tower axial vibration acceleration has been monitored in the frequency band from 0 to 10 Hz with an accelerometer mounted on the gearbox casing between the intermediate and the high-speed shafts. It has been observed that the average frequency spectrum is dominated by the blade passing frequency in all the wind turbines. The evolution of the vibration magnitudes over the entire range of operating conditions is also veiy similar for all the wind turbines. The root-meansquare (rms) acceleration value has been correlated with the wind speed, and it has been found that a linear fit with a positive slope is a useful model for prediction purposes. [ABSTRACT FROM AUTHOR]

As a kind of pump with low head and large capacity, the mixed-flow pump is widely used in large quantities of fields including water conservancy and sewage system of municipal works and so on. The pressure pulsation and flow-induced noise of pump have become two of the most important issues which have negative effect on reliability. The pressure pulsation is the interior performance of the unsteady flow in the pump and the flow-induced noise and vibration are the exterior performance of the unsteady flow in the pump. In order to study the rules of pressure pulsation and flow-induced noise change under different flow rate conditions in a mixed-flow pump and to find the relationship between pressure pulsation and flow-induced noise, the flow field and sound field were numerical simulated. This paper used the PRO/E software to build the pump model and to use the ICEM CFD to conduct the mesh division of the calculated domain. The mixed-flow pump mainly consisted of inlet pipe, impeller, volute and discharge pipe. The unsteady flow was numerical simulated based on RANS solver and SST turbulence model. During the unsteady simulation, the mixed-flow pump rotated for 18 cycles so as to improve the simulation stability. The simulation results of the last 2 periods were used to analyze the time domain characteristics and frequency domain characteristics of pressure pulsation in the pump. And by using the pressure pulsation on the blade as noise source, acoustic Boundary Element Method (BEM) was applied to simulate the flow-induced noise of the mixed-flow pump. The simulation results show that the pressure pulsation amplitude decreases from shroud to hub both at the inlet and outlet of the impeller, and the maximum pressure pulsation appears at the inlet of impeller. So it is crucial to conduct some optimal design for the shroud location in order to weaken the pressure pulsation. Along the circumferential direction in the volute, the pressure pulsation amplitude appears to be the largest near the tongue, the pressure pulsation decreases with the increase of circular angles. And at the outlet of volute, the pressure pulsation appears approximately to be nothing which indicates the flow at this location is steady. The dominant frequency of pressure pulsation in each monitoring point of the mixed-flow pump is always the blade passing frequency under different flow rate conditions. The rotor-stator interaction between the rotating blades and the stationary volute may be the major source of flow-induced noise in the mixed-flow pump. The dominant frequency of flow-induced noise is integral effected by the pressure pulsation and the structure mode of the pump. It is easy to occur resonate between fluid domain and structure domain when the domain frequency of pressure pulsation is closely equal to the domain frequency of the structure mode. The stronger the pressure pulsation is, the more intense the radiation level of corresponding flow-induced noise will produce under the same condition. Weakening the pressure pulsation in the mixed-flow pump is an effective way to reduce the flow-induced noise. This paper has reference value for study on pressure pulsation and flow-induced noise in fluid machinery. [ABSTRACT FROM AUTHOR]

• This advance provides a new tool for cooling tower performance monitoring and maintenance. • Infrasound data was collected persistently outside of two nuclear research reactor cooling towers. • An algorithm was developed to extract cooling tower fan speeds from that infrasound data. • The approach was found to be transferable between facilities as well as between microphone types. Mechanical draft cooling towers (MDCTs) serve a critical heat management role in a variety of industries. For nuclear reactors in particular, the consistent, predictable operation of MDCTs is required to avoid damage to infrastructure and reduce the potential for catastrophic failure. Accurate, reliable measurement of MDCT fan speed is therefore an important maintenance and safety requirement. To that end, we have developed an algorithm for automatically predicting the rotational speeds of multiple, simultaneously operating fan rotors using contactless, infrasound measurements. The algorithm is based on identifying the blade passing frequencies (BPFs), their harmonics, as well as the motor frequencies (MFs) for each fan in operation. Using the algorithm, these frequencies can be automatically identified in the acoustic waveform's short-time Fourier transform spectrogram. Attribution is aided by a set of filters that rely on the unique spectral and temporal characteristics of fan operation, as well as the intrinsic frequency ratios of the BPF harmonics and the BPF/MF signals. The algorithm was tested against infrasound data acquired from infrasound sensors deployed at two research reactors: the Advanced Test Reactor (ATR) located at Idaho National Laboratory (INL) and the High Flux Isotope Reactor (HFIR) located at Oak Ridge National Laboratory (ORNL). After manually identifying the MDCT gearbox ratio, the algorithm was able to quickly yield fan speeds at both reactors in good agreement with ground truth. Ultimately, this work demonstrates the ease by which MDCT fans may be monitored in order to optimize operational conditions and avoid infrastructure damage. [ABSTRACT FROM AUTHOR]

The impeller diameter is one of the fundamental parameters of double channel sewage pumps. In order to analyze the effect of different impeller diameters on pressure fluctuation, the unsteady characteristics of a double channel sewage pump was numerically simulated by using the Mixture multiphase flow model and the developed standard k-e turbulence model. The double channel pump mainly consisted of volute, impeller, inlet extension and outlet extension. In order to improve the calculation stability, the impeller totally rotated for 18 cycles in the simulation and the total computation time was 0.3724 s. The simulation results of the last 2 periods were used to analyze the pressure fluctuation in the pump. Monitoring points were set in the middle of each section in volute circumference and in the tongue region so as to analyze the distribution and variation of the pressure fluctuation with the impeller diameter in the volute especially around the tongue. The calculation results were compared with the experimental data when the impeller diameter was 103 mm. The experiment was conducted in an open test platform, and the test measured the hydraulic performance of the pump and the pressure pulsation of the volute outlet. The pump head and efficiency deviation between calculated and experimental results were 2.37% and -0.46% respectively under the design condition, while the errors were slightly larger but less than 5% under other conditions, which illuminated that the numerical model and calculation methods predicted the hydraulic performance of double channel sewage pump extremely well so that it could be used to predict the characteristics under other impeller diameters. The pressure pulsation trend between calculated and experimental results fitted well and the error was small, which demonstrated that the CFD (computational fluid dynamics) method was able to forecast the distribution and variation of pressure pulsation in the pump accurately. The results showed that the pressure fluctuation of volute circumference under the design condition generally got weaker with the addition of certain amount of particles and the maximum decreased by 30.9%, and the average pressure pulsation reduction of the volute circumferential points decreased with the increase of impeller diameter. The results made clear that selecting appropriate impeller diameter could contribute to prevent pressure pulsation and the induced vibration and noise in the pump when transporting solid-liquid two-phase flow. The pressure fluctuation around the tongue got more and more sharply with the increase of impeller diameter when the water included proper amount of particles. The dominant frequency of points near the tongue was almost the blade passing frequency. Compared with water, the maximum amplitude of the reduction of the pressure pulsation increased and then decreased with the increase of impeller diameter, and the maximum reduction was 22.7%. The lower point of these points in the tongue region was affected maximumly by the rotor-stator interaction between impeller and volute. Instantaneous static pressure of every monitoring point fluctuated sharply when impeller diameter increased to 105 mm under solid-liquid two-phase flow. Selecting the appropriate impeller diameter could contribute to weaken the pressure pulsation when transporting solid-liquid two-phase flow. The study indicates that the impeller diameter has a very important impact on the distribution and variation of the double channel sewage pump and it provides the basis for the optimization design of double channel sewage pump. [ABSTRACT FROM AUTHOR]

Multirotor drone generally controls its attitude and position through the variation of the angular speed of each rotor, which makes the sound signature from it considerably different from the one of single-rotor flight vehicle. Specifically, the sound spectrum of single-rotor vehicles is dominated by the blade passing frequency (BPF) components, determined by the angular speed of the rotor. In contrast, the variation in the angular speed in the multirotor makes it challenging to predict the effects of the multirotor noise. In this study, the effects of the variation in the angular speed of each rotor on the noise of a hovering multirotor were quantified and predicted through uncertainty quantification and single-rotor stochastic analysis. Multirotor experimental results indicated that the Revolution per second (RPS) uncertainty of the multirotor is sensitive to maximum tilt angle and payload. The experimentally quantified angular speed variation is used as input to single-rotor stochastic analysis, and the measured aerodynamic and acoustics results show good agreement with the analytically/numerically predicted results. On comparing multirotor noise, the single-rotor noise with RPS uncertainty results exhibit similar spectral characteristics, especially near the BPF harmonics. Furthermore, the results reveal that the single-rotor stochastic simulation with angular speed uncertainty can predict angular speed variation effects on the multirotor noise in the hovering condition. This study concludes that the sound characteristics of a hovering multirotor can be predicted by considering a single-rotor case with RPS uncertainty. [ABSTRACT FROM AUTHOR]

A large-scale, vaned-voluted centrifugal pump can be applied as the key component in water-transfer projects. Pressure pulsation will be an important factor in affecting the operation stability. This paper researches the propagation and spatial distribution law of blade passing frequency (BPF) and its harmonics on the design condition by numerical simulation. Experimental and numerical monitoring is conducted for pressure pulsation on four discrete points in the vaneless region, which shows that the BPF is dominant. The pulsation tracking network (PTN) is applied to research propagation law and spatial distribution law. It provides a reference for frequency domain information and visualization vaned diffuser. The amplitude of BPF and its harmonics decays rapidly in the vaneless region. BPF and BPF's harmonics influence each other. BPF has local enhancement in the vaneless region when its harmonics attenuate. In the vaned diffuser, the pulsation amplitude of BPF attenuates rapidly, but the local high-pressure pulsation amplitude can be found on the vane blade concave side because of obstruction and accumulation of the vaned diffuser. In the volute, the pulsation amplitude of BPF is low with the decelerating attenuation. This study provides an effective method for understanding the pressure pulsation law in turbomachinery and other engineering flow cases. [ABSTRACT FROM AUTHOR]

This paper develops and proposes an Inverse Tracing Method (ITM) in the time domain to tackle the problem of the radiating noise caused by unsteady propeller sheet cavitation, in which the relationship between the time of the noise source and the time of the propagated sound can be inversely traced by the piecewise cubic-spline functions. By applying the inversely traced relationship into the solution of the wave equation, the Dirac delta function is assumed to simplify to δ (0), so the time integral is assumed to vanish. In addition, the unlimited differential terms also can be replaced by differentiating the piecewise cubic-spline functions. In order to validate the corrections of the ITM, the far-field noise calculated by the ITM is compared with that predicted by the far-field method proposed by Nobel et al. (1986), and good agreement is shown. The near-field noise obtained by the ITM is checked by the experimental results of a container ship, and the ITM overestimates the experimental data by about 2 dB. A workboat is also taken as a computing sample to predict the radiating noise caused by unsteady propeller sheet cavitation. Because the cavity volumes are over-predicted, the predicted noises by the ITM are obviously stronger than the measured noises. As the numerical cavity volumes are modified to meet the measured volumes, by adjusting the cavitation number, the predicted Sound Pressure Level (SPL) at the first blade passing frequency (i.e. the maximum SPL) by the ITM is smaller than the measured value, by 4 dB. At higher blade passing frequencies, the measured SPLs are remarkably stronger than the predicted levels, due to the appearance of tip vortex cavitation in the model test. • Highlight for Reviews. • The proposed scheme (ITM) is a new method, and can predict noises in both near and far fields. • The unlimited differential term can be expressed by the coefficients of the piecewise third-order polynomial. • The validation tests are carried out in both near and far fields for this method (ITM), and good agreements are obtained. • The predicted maximum sound pressure level (SPL) is smaller than the experimental data by 4 dB for the sampled workboat. [ABSTRACT FROM AUTHOR]

Vertical axis wind turbines (VAWT) are a source of renewable energy and are used for both industrial and domestic purposes. The study of noise characteristics of a VAWT is an important performance parameter for the turbine. This study focuses on the development of a linear microphone array and measuring acoustic signals on a cambered five-bladed 45 W VAWT in an anechoic chamber at different tip speed ratios. The sound pressure level spectrum of VAWT shows that tonal noises such as blade passing frequencies dominate at lower frequencies whereas broadband noise corresponds to all audible ranges of frequencies. This study shows that the major portion of noise from the source is dominated by aerodynamic noises generated due to vortex generation and trailing edge serrations. The research also predicts that dynamic stall is evident in the lower Tip speed ratio (TSR) region making smaller TSR values unsuitable for a quiet VAWT. This paper compares the results of linear aeroacoustic array with a 128-MEMS acoustic camera with higher resolution. The study depicts a 3 dB margin between two systems at lower TSR values. The research approves the usage of the 8 mic linear array for small radius rotary machinery considering the results comparison with a NORSONIC camera and its resolution. These observations serve as a basis for noise reduction and blade optimization techniques. [ABSTRACT FROM AUTHOR]

Backflow vortices occasionally occur in the annular mixing zone between the main and axially reverse whirling flows from the impeller tip clearance on an axial pump or compressor. A number (N) of tornado-like backflow vortices rotate around themselves and revolve around the casing axis with a diameter (d) and a revolving angular velocity (ω). To investigate the factors determining N and the movement of the backflow vortices, theoretical analyses are performed. Each backflow vortex is generated in the mixing zone; the core region of each backflow vortex is considered to be a forced vortex, while the outer region is considered to be a free vortex. The ratio (f) of the forced vortex to the distance between the backflow-vortex center and the casing is defined. Each backflow vortex has a circulation and induces movements of all the other backflow vortices depending on the distance between the vortices. The casing restricts the movements of all the backflow vortices, and imaginary image vortices are considered on the other side of the casing. Consequently, for d, ω, N, and f, any parameter can be determined if the other three parameters are specified. As an application of the present theory to an inducer representing an axial pump or compressor, the number (Ncav) of "backflow-vortex cavitations," which occur around the backflow-vortex center, is predicted. Cavitation is visible; therefore, Ncav is quantitatively measurable. In the parameter ranges studied for the tested inducer, the predicted value of N accurately agrees with the experimentally measured value of Ncav. [ABSTRACT FROM AUTHOR]

Pressure fluctuation is the primary factor that affects the stability of turbomachines. The goal of the present work is to explore the propagation of pressure fluctuations in a two-stage double-suction centrifugal pump. The pressure fluctuation characteristics of each component of a two-stage double-suction centrifugal pump are simulated under four typical flow rates based on the SST k-ω turbulence model. It is shown that the pressure fluctuation frequency at blade passing frequency and its first harmonic is the same at the suction chamber, the leading edge, and the middle of the first-stage impeller, which is different from the rotor–stator interaction. Moreover, the uneven impeller inlet flow distribution will produce fluctuations with rotation frequency and its harmonics at the leading edge of the impellers in both stages. Finally, broadband frequency is found at the trailing edge of the impellers in both stages associated with the first harmonic of the rotation frequency, especially under the part load condition. The large size backflow vortex appears in the blade flow channel leading to the low-pressure zone between the impeller, the tongue, and the start of the partition. That is why the pressure drops significantly twice in one rotation period when the blades pass through the tongue and the start of the partition. [ABSTRACT FROM AUTHOR]