Aeroacoustic Analysis Research Articles

Optimizing Duct Geometry for Micro-Scale VAWTs: Exploring Aerodynamics and Aeroacoustics with URANS and DDES Models

Among several advantages of the Vertical Axis Wind Turbines (VAWTs), such as the low cut-in speed, these turbines have lower efficiency compared to Horizontal Axis Wind Turbines (HAWTs). In order to increase the power of VAWTs, a novel approach is employed to address the aforementioned issue. In this study, a convergent-divergent duct (including three components: nozzle, diffuser, and flange) is used, and in the first step of this study, the angles and lengths of all duct components and throat width are optimized (in 3D configuration). In the optimization process, first, the design points are determined by the Design of Experiment (DOE) method, and for each design point, the flow field inside the duct is modeled by the Reynolds-Averaged Navier-Stokes (RANS) approach. Moreover, the objective function of this optimization problem is to maximize the velocity of the flow inside the duct. In the following, the general treatment of the statistical population is forecasted using the Response Surface Method (RSM), and the optimal duct is obtained using the Genetic Algorithm (GA). It is observed that the optimal duct increases the local wind speed up to 1.99 times (from 5 m/s to 9.94 m/s at the throat). Furthermore, a sensitivity analysis was performed on the duct components, which are the most effective parameters in increasing wind speed, nozzle angle, and nozzle length. In the second step, a Darrieus VAWT (with both 2D and 3D configurations) is numerically validated, and then this turbine is scaled-down and located in the optimal duct. The position and tip-clearance of a turbine within the optimal duct are investigated to find the best configuration for higher power generation. Subsequently, both the bare wind turbine and the ducted wind turbine undergo thorough aerodynamic and aeroacoustic analysis, using unsteady RANS and Delayed Detached Eddy Simulations (DDES) approaches, respectively. The results reveal a remarkable improvement in the aerodynamic efficiency (power coefficient increased up to 2.5 times) with the addition of the optimal duct, while the aeroacoustic performance of the system is compromised, leading to an increase in sound pressure level.

Aeroacoustic Analysis of Rotor in Forward Flight Considering Blade Elastic Deformation

Abstract A rotor aeroacoustic calculation model of the rotor in forward flight based on CAMRAD II and FW-H equation was established, which can involve blade elastic deformation. CAMRAD II was used to calculate the actual motion of the blade and the rotor’s unsteady aerodynamic load based on the elastic blade model. The blade dynamics module in the noise calculation program was replaced to consider the blade elastic deformation in forward flight based on the FW-H equation. The forward flight noise characteristics of a full scale rotor were researched. The research shows that the rotor has obvious torsion and flap elastic deformation. The blade elastic deformation has little effect on the directivity of noise in forward flight. In the main noise propagation direction, blade deformation affects the loading noise, resulting in a maximum variation of 3.0dB or more in total noise. In noise calculation, the accuracy of noise prediction can be improved by matching the position of the real blade tip.

Aerodynamic and aeroacoustic analysis of a model UAV propeller

Aerodynamic and aeroacoustic analysis of a model UAV propeller

A numerical analysis of isolated propeller noise using a lattice Boltzmann method approach

Current environmental needs to achieve carbon neutral commercial aviation by 2050 require the development of new technologies and aircraft configurations. Among the different technological developments proposed, the use of open fan or Ultra-High Bypass Ratio configurations is of interest due to their higher propulsive efficiency and performance. To support the development of such technologies, accurate and efficient tools early in the design stages are needed to predict aerodynamic performances and noise levels. One such tool is the lattice Boltzmann method, which can perform high-fidelity aeroacoustic simulations of flows around propellers and engines. The lattice Boltzmann approach can be advantageous over other numerical methods due to its easy integration with complex geometries, its low numerical dissipation properties, and its high level of computational efficiency. This paper presents the aerodynamic and aeroacoustic numerical study of an isolated propeller using the commercial lattice Boltzmann solver ProLB. Large Eddy Simulations were carried out using a compressible hybrid thermal version of the solver. An aeroacoustic analysis using a Ffowcs-Williams and Hawkings acoustic analogy for far-field noise was carried out. The objective is to assess the capabilities of the solver to predict acoustic emissions of an isolated propeller towards the future study of an installed case.

15 years of experience with the Triple Plane Pressure Mode Matching technique

The so-called Triple-Plane-Pressure-Mode-Matching technique (TPP for short) is a method used to isolate and quantify the acoustic part in numerical simulations of turbomachinery. Nowadays, simulations such as Harmonic Balance are commonly applied during the design phase of new turbomachinery components for both aeroacoustic and aeroelastic analyses. The TPP method was first published 20 years ago by Ovenden and Rienstra. The principle is to match the periodic pressure data from three or more neighbouring analysis planes with a subset of acoustic eigenmodes. The original method assumes that the flow in the channel section is potential so that the eigenmodes can be determined analytically. This approach can also be applied in slowly varying ducts. The TPP method is a powerful technique that is used at DLR and MTU Aero Engines. For nearly 15 years, constant joint efforts have been made to improve its applicability in industrial environment. Targeted applications are turbine stages, where the mean flow is complex and vortical wakes contaminate the results. In this paper, the latest developments of the method are presented, including the extension to curved extraction surfaces to enable its application to small blade-row spacing. The utility of the technique is illustrated by an industrial application.

Aeroacoustic analysis of flow induced resonance in a gas pipeline

Flow induced noise and vibration in the pipework of gas production platforms can lead to fatigue failures of attached small-bore pipes, and this can constrain the operating conditions of the platform. Typically such problems comprise a source of turbulence in the flow, an aeroacoustic feedback mechanism due to acoustic resonances inside the pipework, and mechanical resonances which amplify the resulting vibration. The problem described here occurred in the gas metering system of the platform, with the source located in the header which comprised a bifurcation into two metering lines and a number of sharp bends. Because of the cost of rectifying the problem an in-depth study was carried out to analyse the flow and induct acoustic conditions. The predictions will support recommendations for an efficient redesign of the entire system to control the problem at source. Various levels of CFD modelling (RANS and URANS) were carried out using the Openfoam code to predict the exact location and mechanism of the vortex shedding. The acoustic response of the complex ductwork was then modelled using the ACTRAN code to understand the feedback mechanism which led to resonance and high levels of response.

Aeroacoustic analysis of fixed- and variable-pitch controlled multirotors and noise reduction via rotor phase control

This research conducts a comparative analysis of the aerodynamic and aeroacoustic characteristics of fixed-pitch and variable-pitch controlled multirotors (i.e., revolution per minute and collective pitch control). The study encompasses hovering and forward flight conditions, considering wind gust effects. Specifically, high-resolution time-frequency analysis is conducted to investigate the interference and modulation effects of multirotor noise. The analysis reveals significant variations in spectral characteristics depending on the control method. Notably, the frequencies of tonal noise from variable-pitch controlled multirotor do not exhibit short-periodic modulation, in contrast to those of fixed-pitch controlled multirotor. Considering the distinctive spectral characteristics of variable-pitch controlled multirotor, this study explores the effectiveness of noise reduction in variable-pitch controlled multirotor by implementing rotor phase control methods. To validate the noise reduction in time series simulations, a deep learning model is employed to determine the dynamically optimized rotor phases. A multilayer perceptron neural network was trained to derive the optimal rotor phase angles over time, considering the target observer points and flight conditions. The results demonstrate a substantial reduction in noise at the target observer points.

Effect of rotation speed fluctuation on rotor noise generation: A numerical and experimental study

The practical operations of rotors for unmanned aircraft systems can undergo time-varying rotation speeds due to various uncertainty factors. This work investigates the aeroacoustic effect of the rotor’s rotation speed fluctuation using both numerical and experimental approaches. The measured real-time angular speed signal reveals that a hovering rotor experiences highly deterministic rotation speed variations in one revolution, which are closely related to the motor property. Delayed detached eddy simulations are performed, and the fluctuating rotation speed is realized by controlling the mesh displacement at each time step. The results suggest that significant additional tones are produced at the excitation frequency and neighbour frequencies, even though the amplitudes of the rotation speed fluctuations at the dominant frequencies are much smaller than the mean rotation speed. By comparing the full signal to individual harmonic components, it is found that the phase difference between each mode is unimportant. Therefore, the total aeroacoustic effect can be regarded as a linear superposition of different harmonic components. Aeroacoustic source analysis is also performed to isolate the contribution of various source types and correlate the far-field noise with the near-field source distribution. The results show that the extra tonal noise is mostly dominated by the loading noise, with a weaker contribution from the thickness noise. The agreement between the experiments and the simulations indicates that the rotation speed fluctuation is likely responsible for the generation of middle-frequency tonal noise at harmonics of the blade passing frequency.

On-the-Fly Unsteady Adjoint Aerodynamic and Aeroacoustic Optimization Method

An on-the-fly unsteady adjoint-based aerodynamic and aeroacoustic optimization methodology is presented, aiming to achieve practical engineering applications to explore high-efficiency and low-noise design for aerodynamic shapes. Firstly, a novel on-the-fly hybrid CFD-CAA approach is developed with a close integration of unsteady Reynolds-averaged Navier–Stokes equations and a fully viscous time-domain FW-H formulation. Subsequently, an adjoint-based sensitivity analysis method is proposed for unsteady aerodynamic and aeroacoustic problems with either stationary or moving boundaries, wherein a unified architecture for discrete-adjoint sensitivity analysis of both aerodynamics and aeroacoustics is achieved by integrating the on-the-fly hybrid CFD-CAA approach. The on-the-fly approach facilitates direct evaluation of partial derivatives required for solving adjoint equations, eliminating the need for explicitly preprocessing flow and adjoint variables at all time levels in a standalone adjoint CAA solver and consequently substantially reducing memory consumption. The proposed optimization methodology is implemented within an open-source suite SU2. Results show that the proposed on-the-fly adjoint methodology is capable of achieving highly accurate sensitivity derivatives while significantly reducing memory requirements by an order of magnitude, and further demonstrations of single-objective and coupled aerodynamic and aeroacoustic optimizations highlight the potential of the proposed method in exploring high-efficiency and low-noise design for aerodynamic shapes.

Numerical Aerodynamic and Aeroacoustic Analysis of Toroidal Propeller Designs

Drones have a major drawback which prevents them from being used extensively - the excessive noise they produce. This article presents an optimization process of aerodynamic noise reduction for a novel design called the Toroidal Propeller, which consists of two blades looping joined in a manner where the end of one blade arches back into the other, has been designed by the Aerospace Propulsion Systems (APSs) research team at School of Mechanical Engineering, Hanoi University of Science and Technology. In addition, four toroidal propellers with different curved shapes (pitch) and Number of Blades (NOB) are considered. The goal of this research is to evaluate the effects of modifying the geometry design of the Toroidal Propeller on the intensity of blade tip vortex and aerodynamic flow characteristics passing through the blade. The ultimate goal is to decrease blade tip vortex and turbulence produced by the blade, which can help estimate the sound pressure level and minimize it without causing significant performance losses. Based on the outcome results, the models of the four geometry studies are compared in terms of Acoustic Power Level (APL), Surface Acoustic Power Level (SAPL), Thrust, Torque, and Power. In general, the propeller model with NOB of 3 provides the most optimal efficiency in terms of both Thrust and APL. At the output cross-section, the APL dropped from nearly 139 dB to 121 dB, while thrust increased from almost 6.2N to 8.7N compared to the first version of the Toroidal Propeller model.

Development and validity of type II sulcus vocalis in excised canine larynx

AbstractObjectivesThis study aims to develop a sulcus vocalis model in the excised canine larynx and to investigate the validity of the model.MethodsType II sulcus vocalis was created by continuous intradermal suture in six excised canine larynges. We investigated the validity of the model based on phonatory (aerodynamic and acoustic) measures, laryngeal videostroboscopy (LVS), and histological examination. The aeroacoustic parameters included phonation threshold pressure (PTP), fundamental frequency (Fo), jitter %, shimmer %, and harmonics‐to‐noise ratio (HNR).ResultsIn all the experimental specimens, there were significant increases in the PTP ([6.61 ± 1.66] cm H2O, p < 0.01), the Fo ([106.48 ± 49.59] Hz, p = 0.003), the jitter ([0.76 ± 0.42]%, p = 0.007), the shimmer ([6.87 ± 2.99%, p = 0.002]), while the HNR decreased ([5.71 ± 4.68] dB, p = 0.031), compared to that of the untreated canine larynges. The estabilished model simulated the histology with type Ⅱ sulcus.ConclusionsType Ⅱ sulcus vocalis was successfully created in excised canine larynx. The aeroacoustic and LVS analysis of this model resembled the characteristics of patients with sulcus vocalis. The model could be helpful to elucidate the pathology of the phonation, and evaluate and compare the treatments for sulcus vocalis.

Comparative numerical investigation of flow-induced noise characteristics of high-speed trains using high-resolution compressible Large Eddy Simulation

The South Korean Ministry of Land, Infrastructure and Transport has developed a “Comprehensive Plan for 400km/h High-Speed Rail” aimed at enhancing the operational speed of the high-speed railways, currently running up to 300km/h. A short-term goal is to elevate the operating speed of high-speed trains to 370 km/h, up from 320 km/h. Because aerodynamic noise proportionally escalates with the 6th powers of the speed, aerodynamic noise becomes more significant at higher speeds. Consequently, there's a pressing need for design solutions that reduce aerodynamic noise in high-speed trains. This study involves an aeroacoustic analysis using real-scale models of the current model and the preliminary design targeting 370 kph operation. Each model's 8-car formation has been simplified to a 5- car setup. A challenge in predicting aerodynamic noise is the generation of detailed sound sources in the near field and precise noise propagation in the acoustic field. For that, a three-dimensional compressible Large Eddy Simulation technique is employed, utilizing high-resolution grids. This allows for concurrent computation of the external flow and acoustic fields for a real-scale, high-speed train in an open environment. The analysis comprehensively examines the aerodynamic and aeroacoustic properties of each train car, including the major contributors to aerodynamic noise in high-speed trains. The radiated noise is predicted using the Ffowcs Williams and Hawkings equation and is further examined in relation to vortex sound sources.

Isolated propeller aeroacoustics at positive and negative thrust

Using propellers in negative thrust conditions can potentially result in many benefits, such as a steeper descent, a reduced landing run, reduced community noise, energy regeneration, etc. However, the aerodynamics and aeroacoustics of propellers in this regime are not well understood. This paper presents an aeroacoustic analysis of an isolated propeller operating in both positive and negative thrust conditions, using scale-resolved lattice-Boltzmann very large eddy simulations and the Ffowcs Williams & Hawkings analogy. The propeller was operated at a constant tip Mach number so that any differences in tonal noise between positive and negative thrust conditions were due to changes in blade loading. Results showed that the flow separation around the blades in the negative thrust case led to a 2 to 6 times higher standard deviation in integrated thrust compared to the positive thrust case. The blade loading in the negative thrust case shows the amplitude of fluctuations up to 18% for inboard sections and up to 30% near the blade tip compared to the time-averaged loads. The noise in the propeller plane is 10 dB higher in the positive thrust regime than in the negative thrust regime at a given absolute thrust level of |TC|=0.08. The lower noise at negative thrust is caused by two factors: the lower magnitude of the negative torque compared to the positive torque at a given thrust level and the shift of the blade loading inboard in the negative thrust condition due to the stall of the blade tip. Along the propeller axis, the negative thrust regime has 13-15 dB higher noise because of the increased broadband noise generated by the flow separation. In the negative thrust case, the noise along the propeller axis (89 dB) and propeller plane (92 dB) are comparable. However, this is not the case for the propulsive case. The comparison of noise in the vicinity of the propeller plane showed that using the propellers in negative thrust conditions allows for a steeper and quieter descent compared to a conventional descent; as long as the magnitude of the negative torque produced is equal to or less than the torque required to operate the propeller in a conventional landing.

Fluid and aero-acoustic analysis of internal bays: Geometric length-to-depth effects

Weapon bays are essential for any bomber, Next Generation Fighter Aircraft, and unmanned combat air vehicles (UCAVs). As flow approaches the leading edge of such cavity, it separates and forms a shear layer. The structure of bays and residing stores thus become prone to intense acoustic and aerodynamic loading– a major design concern. Cavity flow shows significant dependence on its shape. This makes flow actuation possible by only changing the geometric variable of length-to-depth (L/D) ratio. This study compares two bays with an L/D ratio of 5 (deep) and 10 (shallow) in terms of acoustics and affiliated aerodynamic drag. A transient RANS formulation obtained overall sound pressure levels (OASPL) on bay ceilings. An integral-based method was also used to predict far-field noise propagation due to flow fields of both cavities. It is argued that at Mach 0.6, the character of bays changes remarkably when its L/D is altered. Deeper bays show a smoother pressure profile and significantly less drag while operating in shear mode. Shallow bays, on the other hand, show bluff body type drag with uneven pressure distribution, having the potential of causing downwash on residing stores. At the same time, acoustic loads on the ceiling and acoustic signatures in the far-field are comparable for both cavities.

Performance characterization of a slotted wind turbine airfoil featuring passive blowing

Renewable energy is crucial for a sustainable future, and wind energy holds significant potential as a viable solution to meet global demands. The current study employs high-fidelity Computational Fluid Dynamics (CFD) simulations to investigate the unsteady aerodynamics of an S809 wind turbine airfoil carved with an inclined contracting curved slot at the mid-chord location. The numerical analyses cover a wide range of angles of attack, α = 0°− 20°, at a chord-based Reynolds number of Rec = 5 × 105. The slotted airfoil exhibits superior aerodynamic performance over moderate-to-high angles of attack (α > 6°), with increased lift, reduced drag, and enhanced glide ratio of up to 1.3×, 0.5×, and 3.7× respectively, compared to the baseline. The slot-induced flow control significantly suppresses flow transition and separation across the airfoil surfaces. The attached-flow regime impedes the formation of flow anomalies, resulting in enhanced aerodynamic performance. Comparative analyses reveal significant reductions in velocity fluctuations, Reynolds shear, vorticity, and turbulent kinetic energy, across the slotted airfoil surface and wake region. The aeroacoustic analysis of the slotted airfoil exhibits substantial reduction in the far-field noise over moderate-high angles of attack, with an overall noise level reduction of approximately 14 decibels recorded at α = 17°. Overall, this study highlights the potential of slot-induced flow control as an effective strategy for enhancing the aerodynamic performance of wind turbines.

Aeroacoustic Analysis of Rapid Position Changing Process of Missile Seeker Equipment

A two-dimensional CFD model of the rapid position-changing of missile seeker equipment is presented to study its aeroacoustic impact. By combining the computational fluid dynamics (CFD) with the Ffowcs Williams-Hawkings (FW-H) equation, the flow and related aeroacoustic features are analyzed under different flight Mach numbers and flight heights. The impact of seeker movement on the flow field and aerodynamic noise are highlighted. The results indicate that the spectrum peak of sound pressure level increases with the vortex shedding frequency as the flight Mach number increases. As the flight height of the missile increases, the sound pressure level is amplified while the frequency of vortex shedding decreases.

Airfoil Tonal Noise Prediction Using Urans

Abstract To examine the feasibility of the laminar boundary layer (LBL), vortex shedding (VS) tonal noise modelling using unsteady Reynolds-averaged Navier–Stokes (URANS) was investigated for the non-symmetric S834 airfoil. A transition SST turbulence model was used to model the laminar-turbulent transition and its vital influence on the laminar bubble and hydrodynamic instabilities generation. The influence of turbulence on the unsteady vortex patterns was investigated. Hence, the hybrid aeroacoustic analysis with Lighthill analogy was conducted to obtain the acoustic pressure field. The approach allowed us to model hydrodynamic instabilities and the resulting VS tonal noise. The frequency of VS matched the experimental data, giving the same 1/3 octave tonal peak only for a limited freestream turbulence regime. The simplification of the present method did not allow us to model the aeroacoustic feedback loop, and resulted in lack of instabilities for higher freestream turbulence.

Aeroacoustic analysis of a bass-reflex loudspeaker using LES: Validation of 2D and 3D numerical model with experiment

A bass-reflex loudspeaker has a port that amplifies low frequencies through Helmholtz resonance. However, high sound pressure levels can cause fluid flow near the port tip, leading to noise and distortion. Two-dimensional axisymmetric aeroacoustic analysis is commonly used to predict these non-linear phenomena; however, it has been reported to overestimate harmonic distortion. Presently, its accuracy has not been adequately verified through three-dimensional simulations or comparison with experimental results. This study validates the numerical model by comparing results from three- and two-dimensional analyses with experimental measurements on a straight tube port axisymmetric speaker model. In aeroacoustic analysis, large-eddy simulations are adopted, and the speaker model is acoustically driven at the Helmholtz resonance frequency. The results show that while the two-dimensional axisymmetric model overestimates the harmonic distortion and noise in the frequency response of far-field sound pressure, the three-dimensional model agrees well with the experiment up to the band where the harmonic distortion and port noise appear. This indicates that three-dimensional aeroacoustic analysis is necessary to accurately reproduce the fluid-induced distortion and noise of a bass-reflex port speaker.

Reduction of Flow-Induced Trailing Edge Noise of Semi-Infinite Flat Plate by Structural Resonance

A unique method for the reduction in flow-induced trailing edge noise scattering for a semi-infinite thin plate is proposed by utilizing short flexible panels mounted on the surface of the plate. The proposed configuration differs from conventional cantilevered elastic trailing edges due to the limitations of their structural integrity and applicability. The key idea is to design short panels that vibrate in structural resonance under the fluid loading for absorbing the energy from the flow to sustain their vibration. A time-domain direct aeroacoustic simulation coupled with structural dynamics is carried out at a low Reynolds number of 50,000 to explore the aeroacoustic-structural interactions. The effectiveness of noise reduction of the designed configuration is analyzed by comprehensive aeroacoustic analysis where a significant noise reduction is observed for the plate mounted with three flexible panels without any adverse effects on the plate aerodynamics. The structural analysis shows a systematic vibration pattern for all the panels which clearly indicates the presence of complex fluid-structural interaction under resonance conditions. Design strategy of the proposed configuration along with its limitations are also discussed.

Influence of Door Gap on Aeroacoustics and Structural Response of a Cavity

Numerical aeroacoustic analysis using the Shear Stress Transport–Scale Adaptive Simulation turbulence model was conducted on a weapon bay model based on the M219 geometry with doors incorporating radar cross-section reduction features. The effect of the introduction of a gap between the doors and the cavity edge on the aeroacoustic and structural response of the cavity was analyzed at Mach 0.85. The effect of introducing 3 deg of sideslip was also investigated. Both mean and unsteady flow analyses were conducted. The results showed a strong palliative effect of the door gap with and without sideslips. The overall analysis of the spectral signature on the forces and moments acting on the doors indicated the possibility of fluid–acoustic coupling, as all acoustic spectra showed a predominant tone located at the same frequency of the first structural mode.