H-Darrieus vertical axis wind turbine aerodynamics and aeroacoustics under different inflow conditions

Abstract: The aerodynamics and aeroacoustics of a scaled model H-Darrieus vertical axis wind turbine (VAWT) with end plates and supporting structures is investigated at its design operational regime. A high-fidelity hybrid Lattice Boltzmann Method/Very Large Eddy Simulation model is achieved and coupled to an in-house aeroacoustic propagation code SherFWH based on the Ffowcs Williams and Hawkings’ analogy for noise prediction. A simulation is first performed under uniform inflow conditions to validate the model with available experimental data. A good agreement is seen between the numerical predictions and the experimental noise spectra for both the tonal peaks at the blade passing frequencies and the broadband noise levels. A second simulation is performed with the VAWT titled by an angle of 20? to study the influence of skewed inflow conditions, which are more representative of a typical urban environment. A 12% decrease in the power coefficient and a 2.3 dB decrease in the overall noise level at a given observer position is seen for the skewed inflow model.Communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023

Coarse-grained DEM-CFD simulation of a pilot-scale gaz-fluidized bed

Abstract: Recent studies point CGDEM (Coarse-Grained Discrete Element Method) as a valuable tool to circumvent the cost of original DEM (Discrete Element Method) simulations for large-scale industrial applications such as fluidized beds. In this approach, cost savings are ensured by decreasing the number of particles in the domain, while increasing their size. In the present work, CGDEMLES (Large-Eddy Simulation) numerical simulations are carried out on a 3D cylindrical pilot-scale fluidized bed in the bubbling regime and gathering 9.6M Geldart B-type particles. A macroscopic analysis is performed and allow observing the effects of coarse-graining on the bed behavior qualitatively and quantitatively. Among them, a global homogeneization of the fluidized region, characterized by higher bed surfaces, lower solid velocity and solid fraction gradients, is reported, along with a drop in the bubble population. These effects are observed to intensify as the coarse-graining factor increases. Some of the reported issues can be alleviated by employing additional mechanisms from the literature, aiming at dissipating the extra amount of energy inherently present in coarse-grained systems. However, these are barely sufficient to retrieve DEM results with the smallest coarsegraining factor tested.Communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023

Acoustic far-field prediction of a controlled diffusion airfoil self-noise

Abstract: Direct Numerical Simulations (DNS) of the compressible flow over a Controlled Diffusion (CD) airfoil are conducted. To obtain far field predictions, the DNS are coupled to an acoustic solver based on the Ffowcs Williams & Hawkings formulation. The turbulent flow field at the vicinity of the trailing edge and its noise generation mechanisms is the object of study. The installation effects associated with wind tunnel conditions are included in the computations. Three noise sources have been found, the flow separation and reattachment, the interaction between the attached turbulent flow at the trailing edge and a secondary instability in the near wake.Communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023

Wall-resolved large-eddy simulation of supercritical airfoil side-edge noise

Abstract: A wall-resolved compressible large-eddy simulation and windtunnel experiments are performed on a finite-span supercitical airfoil to investigate the side-edge flow structures and noise sources. The geometry is composed of an isolated supercritical profile (2% camber, 13% thickness) with finite span. The chordwise Reynolds number is 620,000 and the free-stream Mach number is 0.09. The aerodynamic results obtained with a compressible unstructured Large Eddy Simulation solver show the development of turbulent structures from the boundary layer on the airfoil, along with the trajectory of the primary and secondary vorticies. Surface wall shear stress pathlines are compared with experimental oil-flow visualization results yielding good agreement, especially at flow impingement locations. Wall RMS pressure contours highlight the side-edge shear layer and flow impingement of the primary vortex at the pressure side edge to be important noise generation mechanisms. The Ffowcs Williams and Hawkings analogy is used to compute the far-field noise levels. The aeroacoustics simulation results are then compared to the experimental results.Communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023

Aeroacoustic investigation of airfoil at near stall conditions

This paper presents a detailed aeroacoustic investigation of a Controlled-Diffusion airfoil at near stall condition. The study aims at answering two research questions: identify the flow mechanism responsible for separation noise for an airfoil near stall conditions and whether the noise is generated by a dipole for airfoil close to stall and can be quantified by Amiet's diffraction theory. The study uses synchronized PIV, RMP and far-field microphone measurements to perform experiments at two chord based Reynolds numbers of about 150,000 and 250,000. The results show that when the airfoil is placed at a higher angle of attack, such as $15^{\circ}$, strong amplification of flow disturbance is seen, resulting in the rolling up of the shear layer in the aft-region of the airfoil, forming large coherent structures. While these rollers play a central role in the increase in noise due to flow separation, the flapping of shear layer does not contribute to the separation noise. The present study conclusively shows that separation noise is dipolar in nature, and that the quadrupolar contribution for low-speed airfoils at near-stall conditions can be neglected. However, the increase in flow disturbances measured close to the trailing-edge of the airfoil implies that the assumption of small amplitude disturbance is no longer valid, which is the central premise of the thin linearized airfoil theory. Outside the frequency range at which flow separation operates, Amiet's theory is able to predict the far-field noise even at high angles of attack.Comment: 45 pages, 25 figure

Investigating the noise sources of the transonic RAE 2822 airfoil

Abstract: A compressible Large Eddy Simulation is performed on the transonic RAE 2822 airfoil, and compared to the baseline simulation of Koch et al. (28th AIAA/CEAS Aeroacoustics Conference, paper AIAA 2022–2816) in order to highlight the main noise source mechanisms. The new simulation employs a new mesh which eliminates a jump in the airfoil surface mesh, located in the supersonic laminar boundary layer region of the suction side. This jump induced some hydrodynamic instability in the suction side boundary layer of the baseline simulation, potentially emitting noise at high-frequencies. The new results show that these instabilities are significantly damped when employing the new refined mesh and are consequently very sensitive to the grid quality. Nonetheless, the acoustic response of the airfoil, calculated using the Ffowcs Williams and Hawkings analogy in its solid formulation, remains similar to the baseline, with a highfrequency hump appearing between 30 and 40 kHz. This shows that this hump is not caused by the hydrodynamic instabilities, therefore confirming the grid independence of the acoustic results.Communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023

Evaluation of guide parameters for batch torrefaction experiments of refuse-derived fuel

Abstract: Refuse-derived fuel (RDF) is a sustainable energy source that shows a lot of promise in replacing fossil fuels and energy sources. Due to the heterogeneous nature of municipal solid waste and resulting RDF, direct gasification of RDF has seen certain drawbacks in efficiency. Torrefaction is therefore being considered for RDF pre-treatment towards improving the yield of the gasification process. This study involved a series of batch experiments for RDF torrefaction to evaluate the three guide parameters namely, energy yield, mass yield, and energy densification. An oven temperature mapping study is also conducted to establish a standard and repeatable torrefaction methodology. The standard quartering technique is used, before and after grinding to a particle size of <1 mm, to produce reasonably homogenous samples. The batch reactor processed about 21 g of sample for torrefaction at 250?, 300?, and 350? with 30 minutes residence time in all cases. Sealing and nitrogen purging created the required inert atmosphere for the experiments. Mass yield is evaluated as the ratio between the torrefied RDF to the raw RDF. Energy content values are obtained using a bomb calorimeter.Résumé de la communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023

Spectral and wavelet analysis of an aero-acoustic feedback loop in a transonic outflow valve based on Schlieren imaging

International audienceOn commercial aircrafts, the adequate pressure ratio between the cabin and the exterior is regulated with circular outflow valves. At an operating pressure ratio equivalent to 17000ft in altitude, a tonal noise is observed at 11kHz and higher harmonics. A feedback loop is believed to be responsible for this tonal noise and it is studied on an extruded two-dimensional mock-up representative of the outflow valves including the sealing steps. A spectral analysis is performed on the Schlieren images in terms of pixel intensity for each pixel independently. This accentuates the aliasing phenomena of the higher harmonics when studying the maximum power spectral density. In order to highlight different patterns in the flow, phase maps are computed with respect to a particular pixel at 11kHz and harmonics. Last, the feedback mechanism is visible between the sealing step and the valve with the application of a novel wavelet-based technique on the Schlieren images

Experimental investigation of the transient bleed valve noise

This study presents the first step of an experimental study of the transient bleed valve noise. It was carried out on a simplified TBV geometry composed of a cylindrical inlet pipe leading to a diaphragm or a perforated disk for the purpose of generating pressure drops. Numerous diaphragms and grids have been tested in order to identify parameters that influence the acoustic radiation of the TBV and for NPR (Nozzle pressure ratio) from 1.2 to 3.6 to cover both subsonic and supersonic regimes. A large number of acoustic behaviors have been identified. For diaphragms far field acoustic spectra are dominated by mixing noise for all NPR and by shock-associated noise (screech and broadband shock associated noise (BBSAN)) when the critical value of the NPR delimiting the subsonic and supersonic behavior (NPRc = 1.89)is exceeded. For grids the mixing noise is still present but is composed of two humps. The parametric study allowed to associate the first hump to the noise of an equivalent jet having the smallest diameter encircling the grid perforations while the second is associated to the noise of the outer isolated jets. A first prediction model has thus been proposed based on this double source. Furthermore, the grids other a significant noise reduction in the audible range with respect to a diaphragm of the same cross-section by shifting the radiation towards the high frequencies. The noise associated with supersonic phenomena (screech and BBSAN) are also strongly reduced and even suppressed in most of the tested cases