sound pressure level

Investigating the sound radiated from faulty rolling element bearings (REBs) in rotor-bearing systems is as crucial as studying their vibration characteristics. This approach offers experts and researchers a more comprehensive understanding of faulty REB behavior, enhancing fault diagnosis capabilities. This study examines the impact of bearing faults, pedestal looseness, and shaft eccentricity on the vibro-acoustic characteristics of REBs. Additionally, it assesses the influence of fault severity and compound fault scenarios on these behaviors. A 6-degree-of-freedom (DOF) dynamic model is developed for an SKF 6205 bearing, including the shaft, inner ring, outer ring, and pedestal. The Hertzian theory is employed to model contact between the bearing balls and inner/outer rings. The governing equations are solved using the Runge-Kutta method to determine the surface velocity of the REB components, yielding a 4.56% error compared to experimental results, demonstrating good agreement. Based on the surface velocity, the sound pressure level (SPL) is calculated by modeling the inner and outer rings as cylindrical sound sources. The results reveal that auditory and visual observation can identify shaft eccentricity, while sound is a more sensitive indicator of bearing faults. Detecting incipient faults remains challenging, regardless of whether vibration or sound measurement tools, such as accelerometers or sound level meters, are employed. Furthermore, phase portraits indicate that pedestal looseness and bearing faults, unlike shaft eccentricity, result in chaotic and unpredictable motion, which may explain the sudden failures often observed in industrial REBs.

Evaluation of cavitation erosion risk, whether through numerical (CFD) or experimental methods, is crucial in many fluid flow design processes. This risk correlates directly with cavitation signals on affected surfaces. The aim of this study is to optimize the placement of piezoelectric sensors to investigate cavitation-induced erosion on solid surfaces and to enhance the numerical evaluation of their correlation with recorded signals from the sensors. In this study, based on the technical specifications of the K23 tunnel, a convergent-divergent channel has been designed to reduce the pressure in its test section below the vapor pressure, thereby creating the potential for bubble formation on the sample plate. Within this channel, four semi-cylindrical bluff bodies have been utilized as the most effective obstacles to increase cavitation erosion. A quick method for identifying cavitation erosion involves applying a special color to the sample plate. The Film Applicator has been employed as the optimal tool for achieving a uniform color and a thin paint layer on the sample plate. Through CFD modeling, potential cavitation zones are identified under various test conditions to refine the placement of piezoelectric sensors in experimental tests. As a result, piezoelectric sensors are positioned more accurately to measure sound pressure levels. The sound pressure levels obtained using piezoelectric sensors in the time domain, are compared with erosion-induced cavitation zones on the sample test surfaces. The strong agreement between sound pressure levels and observed erosion on the sample plates confirms the accuracy and improvement in the placement of piezoelectric sensors based on CFD modeling.

Acoustic measurements were performed using microphone downstream of a 2-D wind turbine blade section in wind tunnel. The experiments have been carried out in both static and oscillatory pitching cases. The latter is usually experienced by the blades in actual circumstances. The microphone was 1.5 chords downstream of the airfoil and the measurements were conducted at three transverse positions, i.e. behind the trailing edge, midway between the trailing edge and the ground and very close to the ground. A CFD simulation of the flowfield has also been conducted using Fluent to correlate the acoustic behavior to the phenomena observed in the flowfield around the blade. The results show that the acoustic noise heard by a listener located on the ground is higher and stronger than that positioned downstream of the trailing edge, showing the ground effect on acoustic noise reverberation. The aerodynamic noise heard by the listener, changes from a treble to bass sound as the angle of attack increases. Beyond stall, the flow is dominated by the vortices shed into wake and the acoustic noises would be at very low frequencies which would result in a bass sound accompanied by structural vibration. In high angle of attack range, such noises can hardly be heard by a normal person but have a very destructive role on blade structure.

The purpose of this paper is to investigate the effect of aspect ratio on vortex shedding, and transient flow-induced noise over a rectangular cylinder is presented. The freestream velocity is assumed 50 m/s. URANS equations with turbulence model  are employed to flow analysis. Aerodynamic noise calculations are performed using the FW-H analogy. The rectangular cross-section with various lengths and widths is considered. A comparison of the results extracted in the present study with the experimental results of other references indicates the accuracy of the present research. The aspect ratios from 0.6 to 6 (equivalent to Reynolds numbers from 2.5 × 104 to 5.6 × 104) are studied. The simulations can be divided into two categories. In the first category, the ratio of length to width (R = B/H) is less than one, and in the second one, this ratio is greater than one. In the first case, noise is reduced by a relatively low slope. But in the second condition, the behavior of noise is different in various ratios and the slope of noise variations is high. The flow structure is also discussed in this paper. It is founded that for the first category, by increasing the aspect ratio, both the fluctuations and aerodynamic forces are reduced, and the longitudinal wake zone is increased. But in the second category, fluctuations of flow may be increased or decreased in various aspect ratios.

To reduce the noise in a pump piping system and increase the usage time of equipment, a new type of porous muffler is proposed in this paper. A water guide cone is incorporated into the muffler structure, which may help to redirect the fluid media in the piping system. The porous structure is adapted from a muffler shell, water cone wall and round bottom plate. According to this structure, the muffler sample is made, and a pump pipeline system test bench is set up. The outlet noise of the pump pipeline system is measured after installing the muffler. At the same time, the muffler is numerically simulated by combining computational fluid mechanics and Lighthill acoustic theory. The characteristics of the flow field and external sound field under three different flow conditions of 200 m3/h, 400 m3/h and 600 m3/h are assessed. The numerical simulation results show the same dominant frequency and trend as the experimental results. The rationality of the numerical simulation is verified. Research shows that: the level of sound pressure at the muffler's outlet is lower than at the inlet, causing muffling, and the characteristics of a quadrupole sound source appear at the outlet. The proposed muffler has a certain effect in reducing noise in the pump pipeline system.

Metro stations as public places are very important in terms of speech clarity, safety, and security. However, due to the size and physical-special characteristics of these places, the use of non-acoustic materials, and providing acoustical comfort is practically not possible, and in emergencies, hearing voice messages is not possible for people with different mental and physical conditions and workers are prone to hearing damage. The purpose of the study is to assess the acoustic conditions of metro stations to provide auditory satisfaction. Two crucial and distinct stations of Tabriz city were measured using B&K2260 sound level meter. SPL and RT are two of the most significant parameters in users' auditory satisfaction, which are used in the assessment of sound level and speech perception by humans. The measurements and evaluations show that (Lt) in Saat and Khayyam Stations are 106.4 and 104.2 dB, and the minimum is 85.6 and 82.4 dB, respectively. The measured maximum reverberation time (RT) is 7.21 and 5.17 seconds, respectively, at frequencies of 500 and 630 Hz with Gain=-20. According to the values of international standards, both parameters are in the unacceptable range, and in addition to causing irreparable damage to human hearing, in the long run, it covers all sounds, and people are not able to hear the sounds with lower levels than the level of the environmental noise. Therefore, by increasing the surfaces and reducing the volume via architectural elements, it is possible to help improve the acoustical conditions in metro stations.

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

Cavitation phenomenon can cause deterioration of the hydraulic performance, damage by pitting, material erosion, structure vibration and noise in fluid machinery, turbo-machinery, ship propellers and in many other applications. Therefore, it is important to detect inception of cavitation phenomenon. An experimental study has been carried out in order to investigate the noise radiated by various cavitating sources to determine the validity of noise measurements for detecting the onset of cavitation. Measurements have been made measuring the noise radiated by a number of configurations in a water tunnel at various operating condition to determine the onset of cavitation. The measurements have been conducted over a frequency range of 31.5 Hz to 31.5 kHz in one-third octave bands. The onset of cavitation was measured visually through a Perspex side of the working section of the water tunnel. Moreover, a theoretical estimate of the pressure radiated from the cavitation nuclei at their critical radii and their frequency was presented. Tests indicated that, generally, at the point of visual inception there was a marked rise of the sound pressure level in the high-frequency noise, whilst the low-frequency noise increased as the cavitation developed. This finding was supported by the theoretical estimate of the pulsating frequency of cavitation nuclei. The results illustrated that the visual observations of inception confirm the noise measurements.