Pub Date : 2023-06-01DOI: 10.1177/1475472X231183155
Wenyu Chen, Peng Wang, Yingzheng Liu
Acoustic wave scattering and fluid perturbations produced by interactions between incident acoustic wave and confined orifice flow were investigated by a combined numerical solution containing nonlinear flow simulation and linearized acoustic simulation. In flow simulations, the mainstream Reynolds number was fixed at 10,000, which relates to the cooling pipe system of lithography. Turbulent flow fields corresponding to different orifice geometries were solved by an opensource finite volume solver OpenFOAM with Reynolds-averaged Navier–Stokes turbulence model. The turbulence database could efficiently improve the accuracy of subsequent linearized acoustic simulations as the viscosity dissipations were considered. In acoustic simulations, the linearized Navier-Stokes equations were solved by a finite element solver with transformation into frequency domain. The incident acoustic waves with varying frequencies from 500 Hz to 4000 Hz were arranged first at the inlet and then the outlet surfaces, enabling a two-port analysis on the transmission and reflection coefficients of acoustic waves. The numerical setup and the two-port model were well validated by results in literature. Generally, acoustic waves tend to gradually dissipate as their frequencies increase or the opening ratio of the ducted orifice decreases. However, the nonlinear variation in the transmission and reflection coefficients against the frequency variation of the incident acoustic waves could be investigated by increasing the thickness ratio. The acoustically induced fluid perturbations that were characterized by the Q-criterion could form a ring shape vortex structure in the vicinity of the orifice edge and then develop into disk-like packets. When the circumferential shape of the orifice was changed to a square, the attenuation of the incident acoustic waves corresponded to the intensity of the three-dimensionality of the acoustic-induced vortex structures, which indicated a greater energy transfer from the acoustic waves to the fluid perturbations.
{"title":"Numerical simulation on the acoustic wave scattering and fluid perturbations inside confined orifice flow","authors":"Wenyu Chen, Peng Wang, Yingzheng Liu","doi":"10.1177/1475472X231183155","DOIUrl":"https://doi.org/10.1177/1475472X231183155","url":null,"abstract":"Acoustic wave scattering and fluid perturbations produced by interactions between incident acoustic wave and confined orifice flow were investigated by a combined numerical solution containing nonlinear flow simulation and linearized acoustic simulation. In flow simulations, the mainstream Reynolds number was fixed at 10,000, which relates to the cooling pipe system of lithography. Turbulent flow fields corresponding to different orifice geometries were solved by an opensource finite volume solver OpenFOAM with Reynolds-averaged Navier–Stokes turbulence model. The turbulence database could efficiently improve the accuracy of subsequent linearized acoustic simulations as the viscosity dissipations were considered. In acoustic simulations, the linearized Navier-Stokes equations were solved by a finite element solver with transformation into frequency domain. The incident acoustic waves with varying frequencies from 500 Hz to 4000 Hz were arranged first at the inlet and then the outlet surfaces, enabling a two-port analysis on the transmission and reflection coefficients of acoustic waves. The numerical setup and the two-port model were well validated by results in literature. Generally, acoustic waves tend to gradually dissipate as their frequencies increase or the opening ratio of the ducted orifice decreases. However, the nonlinear variation in the transmission and reflection coefficients against the frequency variation of the incident acoustic waves could be investigated by increasing the thickness ratio. The acoustically induced fluid perturbations that were characterized by the Q-criterion could form a ring shape vortex structure in the vicinity of the orifice edge and then develop into disk-like packets. When the circumferential shape of the orifice was changed to a square, the attenuation of the incident acoustic waves corresponded to the intensity of the three-dimensionality of the acoustic-induced vortex structures, which indicated a greater energy transfer from the acoustic waves to the fluid perturbations.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"22 1","pages":"321 - 350"},"PeriodicalIF":1.0,"publicationDate":"2023-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41354443","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-01DOI: 10.1177/1475472X231185082
Ilker Goktepeli, Ulaş Atmaca
Air flow characteristics of an open cavity have been numerically examined by using different turbulence models of Detached Eddy Simulation (DES), k-ε Realizable, k-ω Shear Stress Transport (SST) and Large Eddy Simulation (LES) based on an experimental study of open literature. Numerical results of transient analyses have been compared to experimental results at cavity length-based Reynolds number of Re = 4600. Pressure distributions, streamline patterns, streamwise velocity components, mean velocity values and their vectors have been given in terms of contour graphics. Moreover, velocity profiles have been presented. Pressure fluctuations have been triggered by flow separation and its reattachment. Due to upstream separation of boundary layer, there was curved boundary layer obtained between the outer potential-flow-like and the recirculation zones. As a result, negative velocity values are evidence for rotational flows affected by formation of secondary flows in the cavity. Furthermore, lower pressure region has been observed as a result of rotational flow which was powerful in the open cavity. Numerical results of DES and LES turbulence models are in good agreement with the results of reference study. As the numerical results obtained by LES turbulence model are approximately same with those of experimental reference study, LES turbulence model is mostly recommended. As an option to these turbulence models, k-ω SST model could be utilized for limited computer capacity. However, k-ε Realizable model is not sufficient for capturing rotational flows which are very effective in terms of present case.
{"title":"Examination of air flow characteristics over an open rectangular cavity between the plates","authors":"Ilker Goktepeli, Ulaş Atmaca","doi":"10.1177/1475472X231185082","DOIUrl":"https://doi.org/10.1177/1475472X231185082","url":null,"abstract":"Air flow characteristics of an open cavity have been numerically examined by using different turbulence models of Detached Eddy Simulation (DES), k-ε Realizable, k-ω Shear Stress Transport (SST) and Large Eddy Simulation (LES) based on an experimental study of open literature. Numerical results of transient analyses have been compared to experimental results at cavity length-based Reynolds number of Re = 4600. Pressure distributions, streamline patterns, streamwise velocity components, mean velocity values and their vectors have been given in terms of contour graphics. Moreover, velocity profiles have been presented. Pressure fluctuations have been triggered by flow separation and its reattachment. Due to upstream separation of boundary layer, there was curved boundary layer obtained between the outer potential-flow-like and the recirculation zones. As a result, negative velocity values are evidence for rotational flows affected by formation of secondary flows in the cavity. Furthermore, lower pressure region has been observed as a result of rotational flow which was powerful in the open cavity. Numerical results of DES and LES turbulence models are in good agreement with the results of reference study. As the numerical results obtained by LES turbulence model are approximately same with those of experimental reference study, LES turbulence model is mostly recommended. As an option to these turbulence models, k-ω SST model could be utilized for limited computer capacity. However, k-ε Realizable model is not sufficient for capturing rotational flows which are very effective in terms of present case.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"22 1","pages":"351 - 370"},"PeriodicalIF":1.0,"publicationDate":"2023-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47645745","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-01-20DOI: 10.1177/1475472X231152608
Samuel Afari, R. Mankbadi
A high-fidelity simulation of two in-line counter-rotating propellers in hover, and in forward flight conditions are performed. Near field flow and acoustic properties were resolved using Hybrid LES-Unsteady RANS. Far-field sound predictions were performed using Ffowcs-Williams-Hawkings formulation. The two-propeller results in hovering are compared with that of the single propeller. This enabled us to identify the aerodynamic changes resulting from the proximity of the two propellers to each other and to understand the mechanisms causing the changes in the radiated sound. We then considered the forward flight case and compared it with the corresponding hovering case. This enabled us to identify the aerodynamic changes resulting from the incoming stream. By examining the near acoustic field, the far-field spectra, the Spectral Proper Orthogonal Decomposition, and by conducting periodic averaging, we were able to identify the sources of the changes to the observed tonal and broadband noise.
对两种对旋螺旋桨在悬停和前飞状态下的高保真仿真进行了研究。采用混合les -非定常RANS对近场流场和声学特性进行了解析。采用ffowcs - williams - hawkins公式进行远场声音预测。对双螺旋桨与单螺旋桨的悬停效果进行了比较。这使我们能够确定由于两个螺旋桨彼此接近而导致的空气动力学变化，并了解导致辐射声音变化的机制。然后，我们考虑了向前飞行的情况，并与相应的悬停情况进行了比较。这使我们能够识别来自流入气流的空气动力学变化。通过检查近声场、远场光谱、光谱固有正交分解以及进行周期性平均，我们能够确定观测到的音调和宽带噪声变化的来源。
{"title":"Simulations of multi-rotor interaction noise at hovering & forward flight conditions","authors":"Samuel Afari, R. Mankbadi","doi":"10.1177/1475472X231152608","DOIUrl":"https://doi.org/10.1177/1475472X231152608","url":null,"abstract":"A high-fidelity simulation of two in-line counter-rotating propellers in hover, and in forward flight conditions are performed. Near field flow and acoustic properties were resolved using Hybrid LES-Unsteady RANS. Far-field sound predictions were performed using Ffowcs-Williams-Hawkings formulation. The two-propeller results in hovering are compared with that of the single propeller. This enabled us to identify the aerodynamic changes resulting from the proximity of the two propellers to each other and to understand the mechanisms causing the changes in the radiated sound. We then considered the forward flight case and compared it with the corresponding hovering case. This enabled us to identify the aerodynamic changes resulting from the incoming stream. By examining the near acoustic field, the far-field spectra, the Spectral Proper Orthogonal Decomposition, and by conducting periodic averaging, we were able to identify the sources of the changes to the observed tonal and broadband noise.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"22 1","pages":"153 - 187"},"PeriodicalIF":1.0,"publicationDate":"2023-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43009820","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-01-17DOI: 10.1177/1475472X231152607
Sujit Kumar, Priyanshu Mishra, S. Narayanan
The present paper provides a detailed acoustic characterization of symmetric and asymmetric NACA airfoils for various thickness ratios to determine the best thickness ratio and geometry which provide lower acoustic radiations with respect to the standard NACA0010 airfoil. The studies are conducted for various t/c values of 0.12, 0.15 and 0.21, where t is the airfoil thickness and c is the airfoil chord. The far-field acoustic emissions are observed to decrease with increase in t/c ratios for both the symmetric and asymmetric airfoils. For all the t/c values and jet velocities studied, the asymmetric airfoils show higher noise reductions from mid to high frequencies as compared to the symmetric ones, which might be due to the reduced transverse velocity fluctuations as a result of the large distortions imparted to oncoming turbulent gust by the formation of the larger stagnation pressure zone. The symmetric airfoils show a maximum reduction up to 3 dB from mid to high frequencies while asymmetric ones show a reduction up to about 5 dB. An empirical expression is developed for the ΔOAPWL as a function of t/c only for both the symmetric and asymmetric airfoils, where ΔOAPWL is the overall sound power reduction level in dB. It reveals that the ΔOAPWL follow a second order polynomial for both the symmetric and asymmetric airfoils at all jet velocities studied. It is observed that thicker (i.e., t/c = 0.21) symmetric and asymmetric airfoils show lower acoustic radiations as compared to the thinner ones for all the emission angles. In general, it is observed that the thinner airfoils show higher directivity as compared thicker ones, albeit they show a common trait of downstream directivity. Further the highest directivity is seen at an emission angle of 67.5° for both the symmetric and asymmetric airfoils. Thus, the present study clearly demonstrates that the airfoils with higher t/c ratios could be considered as the best passive means for achieving substantial reductions of airfoil broadband noise over a wide range of frequencies.
{"title":"Investigations of thickness effects on the acoustic characteristics of symmetric and asymmetric airfoils","authors":"Sujit Kumar, Priyanshu Mishra, S. Narayanan","doi":"10.1177/1475472X231152607","DOIUrl":"https://doi.org/10.1177/1475472X231152607","url":null,"abstract":"The present paper provides a detailed acoustic characterization of symmetric and asymmetric NACA airfoils for various thickness ratios to determine the best thickness ratio and geometry which provide lower acoustic radiations with respect to the standard NACA0010 airfoil. The studies are conducted for various t/c values of 0.12, 0.15 and 0.21, where t is the airfoil thickness and c is the airfoil chord. The far-field acoustic emissions are observed to decrease with increase in t/c ratios for both the symmetric and asymmetric airfoils. For all the t/c values and jet velocities studied, the asymmetric airfoils show higher noise reductions from mid to high frequencies as compared to the symmetric ones, which might be due to the reduced transverse velocity fluctuations as a result of the large distortions imparted to oncoming turbulent gust by the formation of the larger stagnation pressure zone. The symmetric airfoils show a maximum reduction up to 3 dB from mid to high frequencies while asymmetric ones show a reduction up to about 5 dB. An empirical expression is developed for the ΔOAPWL as a function of t/c only for both the symmetric and asymmetric airfoils, where ΔOAPWL is the overall sound power reduction level in dB. It reveals that the ΔOAPWL follow a second order polynomial for both the symmetric and asymmetric airfoils at all jet velocities studied. It is observed that thicker (i.e., t/c = 0.21) symmetric and asymmetric airfoils show lower acoustic radiations as compared to the thinner ones for all the emission angles. In general, it is observed that the thinner airfoils show higher directivity as compared thicker ones, albeit they show a common trait of downstream directivity. Further the highest directivity is seen at an emission angle of 67.5° for both the symmetric and asymmetric airfoils. Thus, the present study clearly demonstrates that the airfoils with higher t/c ratios could be considered as the best passive means for achieving substantial reductions of airfoil broadband noise over a wide range of frequencies.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"22 1","pages":"188 - 206"},"PeriodicalIF":1.0,"publicationDate":"2023-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46991682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-01-11DOI: 10.1177/1475472X221150176
A. Karn, Ritvik Anand, Aditya Kataria, R. Donga, Naman Agarwal, V. Singh
The physics of music has been well studied and has provided the basis on which musical instruments are made, studied and characterized. Significant research has been conducted on the different kinds of musical instruments, which range from traditional instruments like the mridangas of India to the bagpipes of Scotland. In fact, a lot of research has been carried on the acoustics of different kinds of flutes as well, such as the Finnish kantele and the Indonesian Kompangs. The Indian subcontinent, the birthplace of transverse flutes and a host of other instruments, itself has a plethora of unique musical instruments that have been scientifically examined. Yet, the Bastar flutes of India have evaded the due scientific attention that they deserve owing to their unique sound generation mechanism. Quite strangely and surprisingly, these Bastar flutes are a unique genre of flutes that don’t require lips to be played, and are quite intriguing. The current research explores the aeroacoustics of a Bastar flute via experimental measurements, computational simulations and analytical formulations. The results demonstrate that the amplitude produced is directly proportional to the number of rims present. This are also responsible for producing a low-frequency, high-amplitude melodious sound. It also suggests that the underlying mechanism behind sound generation in a Bastar flute is a unique blend of edge tone and a jet tone, demonstrating a rare phenomenon not seen in traditional musical instruments. This uncommon phenomenon has the potential to unlock several new applications in the field of acoustics.
{"title":"Playing flute without lips? Tones of music lost in time: An investigation of the indigenous Bastar flutes of India","authors":"A. Karn, Ritvik Anand, Aditya Kataria, R. Donga, Naman Agarwal, V. Singh","doi":"10.1177/1475472X221150176","DOIUrl":"https://doi.org/10.1177/1475472X221150176","url":null,"abstract":"The physics of music has been well studied and has provided the basis on which musical instruments are made, studied and characterized. Significant research has been conducted on the different kinds of musical instruments, which range from traditional instruments like the mridangas of India to the bagpipes of Scotland. In fact, a lot of research has been carried on the acoustics of different kinds of flutes as well, such as the Finnish kantele and the Indonesian Kompangs. The Indian subcontinent, the birthplace of transverse flutes and a host of other instruments, itself has a plethora of unique musical instruments that have been scientifically examined. Yet, the Bastar flutes of India have evaded the due scientific attention that they deserve owing to their unique sound generation mechanism. Quite strangely and surprisingly, these Bastar flutes are a unique genre of flutes that don’t require lips to be played, and are quite intriguing. The current research explores the aeroacoustics of a Bastar flute via experimental measurements, computational simulations and analytical formulations. The results demonstrate that the amplitude produced is directly proportional to the number of rims present. This are also responsible for producing a low-frequency, high-amplitude melodious sound. It also suggests that the underlying mechanism behind sound generation in a Bastar flute is a unique blend of edge tone and a jet tone, demonstrating a rare phenomenon not seen in traditional musical instruments. This uncommon phenomenon has the potential to unlock several new applications in the field of acoustics.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"22 1","pages":"110 - 130"},"PeriodicalIF":1.0,"publicationDate":"2023-01-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41960252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-01-10DOI: 10.1177/1475472X221150173
Dhanush Vittal-Shenoy, R. Gojon, T. Jardin, Marc C. Jacob
The aeroacoustics of an SD7003 airfoil at Reynolds number 60,000 is investigated using Large Eddy Simulation. Five simulations are performed to study the effects of angle-of-attack and Mach number at fixed Reynolds number. For the three cases with angle-of-attack equal to 0° (M = 0.1, 0.3 and 0.6), a pure tonal noise associated with a 2D organisation of the flow is obtained. This flow topology is due to the establishment of a well known aeroacoustic feedback loop between the separation point on the suction side of the airfoil and the trailing edge. The occurrence of this loop is corroborated by the presence of a standing wave pattern with characteristic mode number in accordance with Panda’s model. The main effect of the Mach number is to promote flow separation and hence increase separation length and mode number. In addition, the first harmonic and the sub-harmonic of the tone, observed in the far field acoustic spectrum, are found to be generated in the wake, presumably due to non-linear vortex interactions. For the two other angles-of-attack 4° and 8° at M = 0.1, the feedback loop does not establish and a Laminar Separation Bubble (LSB) is observed. When increasing the angle-of-attack, the LSB shrinks with earlier reattachment. For those two cases, far-field spectra are characterized by a low frequency associated with the breathing motion of the LSB and the reattachment point fluctuating in space. The frequency of this fluctuation depends on the curvature of the bubble. Far-field spectra are also characterized by a broadband trailing edge noise whose frequency range decreases with the angle-of-attack. Again, this evolution is found to depend on the curvature of the bubble which may promote a centrifugal instability in the separated shear layer.
{"title":"Angle-of-attack and Mach number effects on the aeroacoustics of an SD7003 airfoil at Reynolds number 60,000","authors":"Dhanush Vittal-Shenoy, R. Gojon, T. Jardin, Marc C. Jacob","doi":"10.1177/1475472X221150173","DOIUrl":"https://doi.org/10.1177/1475472X221150173","url":null,"abstract":"The aeroacoustics of an SD7003 airfoil at Reynolds number 60,000 is investigated using Large Eddy Simulation. Five simulations are performed to study the effects of angle-of-attack and Mach number at fixed Reynolds number. For the three cases with angle-of-attack equal to 0° (M = 0.1, 0.3 and 0.6), a pure tonal noise associated with a 2D organisation of the flow is obtained. This flow topology is due to the establishment of a well known aeroacoustic feedback loop between the separation point on the suction side of the airfoil and the trailing edge. The occurrence of this loop is corroborated by the presence of a standing wave pattern with characteristic mode number in accordance with Panda’s model. The main effect of the Mach number is to promote flow separation and hence increase separation length and mode number. In addition, the first harmonic and the sub-harmonic of the tone, observed in the far field acoustic spectrum, are found to be generated in the wake, presumably due to non-linear vortex interactions. For the two other angles-of-attack 4° and 8° at M = 0.1, the feedback loop does not establish and a Laminar Separation Bubble (LSB) is observed. When increasing the angle-of-attack, the LSB shrinks with earlier reattachment. For those two cases, far-field spectra are characterized by a low frequency associated with the breathing motion of the LSB and the reattachment point fluctuating in space. The frequency of this fluctuation depends on the curvature of the bubble. Far-field spectra are also characterized by a broadband trailing edge noise whose frequency range decreases with the angle-of-attack. Again, this evolution is found to depend on the curvature of the bubble which may promote a centrifugal instability in the separated shear layer.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"22 1","pages":"131 - 152"},"PeriodicalIF":1.0,"publicationDate":"2023-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49022594","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-01-09DOI: 10.1177/1475472X221150181
T. Jardin, R. Gojon, N. Doué, H. Parisot-Dupuis
We compare medium and high fidelity numerical simulations to experiments conducted on low Reynolds number rotors typical of small scale Unmanned Aircraft Systems (UAS). We first show that these numerical approaches provide reasonable estimates of the aerodynamic performance and farfield tonal noise and hence apply them for the investigation of the influence of solidity ratio on the aerodynamics and acoustics of small scale rotors operating under hovering, iso-thrust conditions. We show that while solidity ratio has a weak impact on aerodynamic performance, it may help drastically reduce farfield tonal noise. This reduction is however found to depend on the interplay between thickness and loading noise such that increasing the solidity by increasing the number of blades at constant blades’ aspect ratio or by decreasing the blades’ aspect ratio keeping the number of blades constant may yield very different, sometimes opposite, trends.
{"title":"Numerical and experimental analysis of the influence of solidity on rotor aeroacoustics at low Reynolds numbers","authors":"T. Jardin, R. Gojon, N. Doué, H. Parisot-Dupuis","doi":"10.1177/1475472X221150181","DOIUrl":"https://doi.org/10.1177/1475472X221150181","url":null,"abstract":"We compare medium and high fidelity numerical simulations to experiments conducted on low Reynolds number rotors typical of small scale Unmanned Aircraft Systems (UAS). We first show that these numerical approaches provide reasonable estimates of the aerodynamic performance and farfield tonal noise and hence apply them for the investigation of the influence of solidity ratio on the aerodynamics and acoustics of small scale rotors operating under hovering, iso-thrust conditions. We show that while solidity ratio has a weak impact on aerodynamic performance, it may help drastically reduce farfield tonal noise. This reduction is however found to depend on the interplay between thickness and loading noise such that increasing the solidity by increasing the number of blades at constant blades’ aspect ratio or by decreasing the blades’ aspect ratio keeping the number of blades constant may yield very different, sometimes opposite, trends.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"22 1","pages":"85 - 109"},"PeriodicalIF":1.0,"publicationDate":"2023-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48142042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-01-03DOI: 10.1177/1475472X221150170
Harinath Reddy Nakkala, Krishnamurthy Srinivasan
The offset jet configuration is one where the jet is discharged at some distance from a solid surface. Although the geometric configuration may look simple, the flow may involve several complexities. In propulsion systems, the high-speed jet generated from the rear engine of an aircraft, flowing nearby the fuselage, can be treated as an offset jet. In this work, an experimental investigation of the interaction noise due to circular high-speed offset jets is performed in an anechoic environment at different nozzle pressure ratios and offset ratios (height of the jet centerline above the plate per nozzle width). A large horizontal plate placed over a height-adjustable stand is used as the offset plate. Acoustic characteristics such as overall sound pressure level and the directivity pattern of free and offset jets are compared for different nozzle pressure ratios. The effect of offset ratio on noise characteristics is also investigated. Flow visualization is also carried out to understand the shock structure and its noise generation mechanism. Acoustic characteristics reveal that noise levels are higher for an offset jet compared to a free jet. Sound pressure levels for offset ratio 0.5 are lower than those for other offset ratios. The noise levels are higher for offset ratio 1.0 due to the presence of feedback tone. Schlieren visualization studies also corroborate the above characteristics.
{"title":"Aeroacoustic characteristics of supersonic offset jets","authors":"Harinath Reddy Nakkala, Krishnamurthy Srinivasan","doi":"10.1177/1475472X221150170","DOIUrl":"https://doi.org/10.1177/1475472X221150170","url":null,"abstract":"The offset jet configuration is one where the jet is discharged at some distance from a solid surface. Although the geometric configuration may look simple, the flow may involve several complexities. In propulsion systems, the high-speed jet generated from the rear engine of an aircraft, flowing nearby the fuselage, can be treated as an offset jet. In this work, an experimental investigation of the interaction noise due to circular high-speed offset jets is performed in an anechoic environment at different nozzle pressure ratios and offset ratios (height of the jet centerline above the plate per nozzle width). A large horizontal plate placed over a height-adjustable stand is used as the offset plate. Acoustic characteristics such as overall sound pressure level and the directivity pattern of free and offset jets are compared for different nozzle pressure ratios. The effect of offset ratio on noise characteristics is also investigated. Flow visualization is also carried out to understand the shock structure and its noise generation mechanism. Acoustic characteristics reveal that noise levels are higher for an offset jet compared to a free jet. Sound pressure levels for offset ratio 0.5 are lower than those for other offset ratios. The noise levels are higher for offset ratio 1.0 due to the presence of feedback tone. Schlieren visualization studies also corroborate the above characteristics.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"22 1","pages":"5 - 22"},"PeriodicalIF":1.0,"publicationDate":"2023-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47939555","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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