Wide Range Of Flows Research Articles

On the Numerical Investigation of Natural-Convection Heat Sinks Across a Wide Range of Flow and Operating Conditions

Many designs for natural-convection heat sinks and semi-empirical correlations have been proposed in the recent years, but they are only valid in a limited range of Elenbaas numbers El and were mostly tested for laminar flows. To alleviate those limits, parametric studies with 2D and quasi-3D models were carried out, in ranges of Grashof numbers up to 1.55×1011 and Elenbaas numbers up to 3.42×107. Ansys Fluent’s laminar, transition-SST, SST k-ω and k-ϵ models were applied. In addition, when used in this valid range, i.e., mean Elenbaas numbers, with the simplified quasi-3D model, the transition-SST model could predict better results, overestimating the heat flux by 10 to 15% compared to semi-empirical correlations. The 2D model was not deemed satisfying, regarding turbulence models. Consequently, a quasi-3D model was developed: it appeared to be an efficient trade-off between computational time and prediction accuracy, in particular for turbulence models. New grouping factors were also found, to ensure proper dimensioning of natural-convection heat sinks. They corresponded to non-dimensional parameters that dictated the physical behaviour of the heat sink with respect to the semi-empirical correlations. Typically, the ratio of the spacing to the optimal spacing predicted by Bar-Cohen’s correlation turned out to be an appropriate grouping factor with a threshold of 1, above which the fins could safely be considered as isolated, thus greatly simplifying all further calculations.

Strong evidence for universality in homogeneous compressible turbulence

Quantifying the degree of universality in compressible turbulence is challenging due to the existence of different modes and their complex interactions. For a restricted family of flows, Donzis and John [Phys. Rev. Fluids 5, 084609 (2020)] showed that universal behavior is indeed observed in compressible turbulence if the ratio of dilatational to solenoidal root mean square (rms) velocities (δ=u′d/u′s) is incorporated as a scaling parameter along with the traditional turbulent Mach number (Mt=u′/〈c〉, where u′ is the rms velocity and 〈c〉 is the mean speed of sound). In this paper, we argue for the generality of those results by analyzing a wide range of compressible turbulent flows spanning a variety of flow configurations and setups to assess the degree of universal behavior. These include, among others, reacting flows, flows with solenoidal, thermal, and dilatational forcing, and flows with mean shear and bulk viscosity. We also performed new direct numerical simulations, which include turbulence in situations where vibrational modes of constitutive molecules are not in thermal equilibrium. Collectively, we offer the largest comparison across studies in the literature to date. We find that despite the wide range of forcing conditions and physical processes, universality holds across all these turbulent flows to a very satisfactory degree when both δ and Mt are considered as intrinsic compressibility parameters. The statistics investigated here—single-point statistics up to order four—are chosen such that they represent different ranges across the spectrum of dynamically relevant turbulence scales. We discuss the applicability of the purposed universal behavior for other key statistics in these turbulent flows, including two-point statistics and inhomogeneity effects, and the perspective it opens for modeling them.

Strategies for Enhancing One-Equation Turbulence Model Predictions Using Gene-Expression Programming

This paper introduces innovative approaches to enhance and develop one-equation RANS models using gene-expression programming. Two distinct strategies are explored: overcoming the limitations of the Boussinesq hypothesis and formulating a novel one-equation turbulence model that can accurately predict a wide range of turbulent wall-bounded flows. A comparative analysis of these strategies highlights their potential for advancing RANS modeling capabilities. The study employs a single-case CFD-driven machine learning framework, demonstrating that machine-informed models significantly improve predictive accuracy, especially when baseline RANS predictions diverge from established benchmarks. Using existing training data, symbolic regression provides valuable insights into the underlying physics by eliminating ineffective strategies. This highlights the broader significance of machine learning beyond developing turbulence closures for specific cases.

Aerodynamic instability evolution of a multi-stage combined compressor

Unstable operating conditions such as surge could cause damage to both aerodynamic performance and structural integrity of a compression system. This paper addresses the critical issue of aerodynamic instability in compressor design, particularly focusing on an axial-centrifugal combined compressor, a widely used yet underexplored configuration. An experimental investigation was conducted on a three-stage axial and one-stage centrifugal compressor (3A1C), using two pipe systems and employing fast-responding transducers to capture the dynamic instability process from choke condition to deep surge. Results reveal that at the design speed, 3A1C enters deep surge directly, whereas at off-design speeds, it experiences rotating stall and mild surge across a wide mass flow range. Some special instability features in the combined compressor can be found in the steady state map and dynamic process. The characteristic curve of the first axial stage keeps a positive slope during the whole mass flow range at an off-design speed. The first stage could work stably on the stall characteristic curve because the centrifugal stage has stronger pressurization and plays a dominant role in global aerodynamic instability. Besides, rotating instability occurs at the first rotor tip and disappears as the back pressure increases, which is also rarely seen in a single-axial compressor. This is also related to the strong pressurization of the centrifugal stage. The findings of this paper will contribute to the understanding of aerodynamic instabilities in combined compressors.

Wall Modeling of Turbulent Flows with Varying Pressure Gradients Using Multi-Agent Reinforcement Learning

We propose a framework for developing wall models for large-eddy simulation that is able to capture pressure-gradient effects using multi-agent reinforcement learning. Within this framework, the distributed reinforcement learning agents receive off-wall environmental states, including pressure gradient and turbulence strain rate, ensuring adaptability to a wide range of flows characterized by pressure-gradient effects and separations. Based on these states, the agents determine an action to adjust the wall eddy viscosity and, consequently, the wall-shear stress. The model training is in situ with wall-modeled large-eddy simulation grid resolutions and does not rely on the instantaneous velocity fields from high-fidelity simulations. Throughout the training, the agents compute rewards from the relative error in the estimated wall-shear stress, which allows them to refine an optimal control policy that minimizes prediction errors. Employing this framework, wall models are trained for two distinct subgrid-scale models using low-Reynolds-number flow over periodic hills. These models are validated through simulations of flows over periodic hills at higher Reynolds numbers and flows over the Boeing Gaussian bump. The developed wall models successfully capture the acceleration and deceleration of wall-bounded turbulent flows under pressure gradients and outperform the equilibrium wall model in predicting skin friction.

Implementation of a Drift Flux Model into SAM with Development of a Verification and Validation Test Suite for Modeling of Noncondensable Gas Mixtures

The advanced thermal-hydraulic system code, System Analysis Module (SAM), was originally developed for the modeling of single-phase flow in advanced reactors. It has since been expanded to include a four-equation drift flux model for the modeling of two-phase flows containing a noncondensable gas. The model was expanded to support the modeling of molten salt reactor (MSR) designs in which the fuel is directly dissolved in the circulating coolant. These designs have shown that circulating gas bubbles can play an important role in the management of fission products and the operational behavior of the reactor. A drift flux model was implemented to more accurately capture the localized behavior of the void in the core and its impact on the mass transfer of fission products. A thorough assessment of the new model was performed by developing a verification and validation test suite. Verification problems were designed to test all major terms in the new governing equations. The new model converged to the correct solution at the expected order of accuracy for all verification cases. The validation cases included a wide range of flow and void conditions in different pipe geometries. Although higher void experiments show a slight underprediction of void by the drift flux model, experiments that aim to reproduce Molten Salt Reactor Experiment (MSRE) experimental conditions show good agreement with the model. The gas transport model was activated for a SAM model of the MSRE to demonstrate that it can be used in a more complex model. This gas transport model will be used along with an interfacial area transport equation being implemented in SAM for the prediction of mass transport behavior in MSR conditions.

Hydraulic conditions created by a ‘large’ diameter Cylindrical Bristle Cluster fish pass

Cylindrical Bristle Clusters (CBCs) provide a multi-species fish passage solution at sloped weirs. Configurations trialled to date (min. diagonal spacing between CBCs up to 0.17 m) were designed to facilitate passage of relatively small (e.g. < 30 cm) potamodromous species and may hamper the movements of larger bodied (e.g. > 40 cm) fishes, such as adult anadromous salmonids. Therefore, in this study, the hydraulic conditions created by an array of large diameter (0.13 m) CBCs positioned farther apart than in previous studies (min. diagonal spacing 0.29 m) was assessed to determine whether conditions would be suitable for facilitating the passage of small-bodied fish while also providing sufficient space for larger individuals to manoeuvre. Two experiments were conducted in an open channel flume. Experiment 1 quantified the hydraulic conditions created by a model Crump weir when unmodified and with CBCs installed in supercritical flow (Fr 1.23–3.01) on the 1:5 downstream sloping face under a low (0.08 m3 s−1) and high (0.23 m3 s−1) discharge. Patches of low water velocity were created in the wake of the CBCs, and the median (time and space averaged) velocity was reduced under both low (30.1%) and high (22.3%) discharge. Based on estimated burst swimming speeds of two common European species, the roach (Rutilus rutilus) and brown trout (Salmo trutta) (0.16 m long, swimming at 15.1 °C), this reduction in velocity would facilitate upstream passage. Experiment 2 documented the vertical velocity profile and shear stress characteristics (a measure of turbulence) within the CBC array. Unlike in Experiment 1, the CBCs were installed on the flat base of the flume and under subcritical flow (Fr = 0.31) to generate sufficient water depth. The velocity was reduced (up to 22.5%) at depths that did not exceed (> 2 cm above) the height of the bristles. Above these depths, velocity was (up to 14.6%) higher compared to open channel conditions upstream of the CBC array and a vertical shear layer was evident. As the main hydraulic benefits of CBCs occur at depths that do not exceed the bristles, their height should be tailored to site specific conditions (e.g. size of target fish species and/or depth of water at infrastructure). Field-based research is needed to determine velocity reduction at longer weirs and under a wider range of flows than can be tested under flume conditions. How the hydraulic characteristics of submerged CBCs differ from those described here with those that occur in the field when installed on a steep sloping weir under supercritical flow should be further investigated.

Permeability of granular mixtures under shear

Fluidised granular flows are gas–particle mixtures that occur in a wide range of industrial applications and geophysical flows. One factor governing the fluidisation behaviour of a granular flow is its permeability — the ability of the gas to move through the particle column. Although extensive research has been carried out on the gas–particle permeability under static conditions, most of the industrial and geophysical processes are dynamic phenomena, where parameters such as the shear rate change with both time and space. Here, the effects of shear rate on the permeability of gas–particle mixtures were studied through novel experiments where a granular column comprising particles of diameter 63–250 μm was sheared at shear rates between 0 and 213s−1 while an increasing flux of compressed air was introduced into the base of the column. Regardless of the shear rate, the granular column starts to expand upon increasing the air velocity, however, columns sheared at higher rates require greater air velocities to exhibit bubbling (and column expansion). We also instrumented the column with a pressure sensor. For the static column, as the air velocity increases, the pressure gradient across the granular column increases linearly until it reaches a maximum value, slightly decreases, and then plateaus. Conversely, for high shear rates, the pressure gradient continuously increases with increased air velocity, never reaching a maximum value or a plateau. The pressure gradient data were analysed alongside the videography in terms of the minimum fluidisation velocity and the minimum bubbling velocity, and both were found to be greater for higher shear rates. Consequently, our results show that increased shear increases the permeability of granular columns and the experimental data further suggests that in order to accurately describe the evolution of the pressure gradient across a sheared granular column, processes in the vertical as well as radial plane should be taken into account.

A new LED-based extinction tomography method for measurement of aerosol surface area

A light-emitting-diode (LED) based optical technique is developed to measure the surface area per unit volume of particles in aerosols and liquid sprays. The technique uses path-integrated measurements of transmittance, T, from two angles to produce a tomographic reconstruction of the local extinction coefficients, K, in the region of interest, using the Beer-Lambert law and a deconvolution algorithm. When the particles in the flow have sufficiently large diameters (existing in the Mie scattering regime), these extinction coefficients can be related to the surface area per unit volume of the particles. The technique has the potential to be applied to a wide range of two-phase flows. In the present study, it is applied to flows through a pharmaceutical inhaler device, where two powders with different particle size distributions are considered.

Rock fishways: Natural designs for an engineered world

Globally, fishways have been constructed as a technical solution to reduce the damaging effects of dams and weirs on fish movement. Some common design typologies are rock fishways and nature-like bypasses. While rock fishways are common in Australian rivers, there has been no general evaluation of their effectiveness, location, or costs to demonstrate their success and help guide future investment. Our objective was to develop an Australian inventory of rock fishways to visualise their location, major design elements, capital cost and frequency of evaluation. We also present two rock fishway case-studies that highlight key ecological and engineering design criteria, field evaluation of effectiveness and a summary of construction learnings. In Australia, there were 332 rock fishways, most typologies were lateral-ridge rock ramps (161), random rock fishways (123), nature-like bypasses (13) and hybrid designs (10). Approximately 20% of these have biological monitoring. Trends over time, included: (i) a slight flattening of fishway slope (from 1 V:20H to 1 V:30H) (ii) a progression from dumped loose rock to keyed-in formalised lateral-ridge fishways, increased use of natural sealing and (iii) an emerging tendency to hybrid concrete baffle and rock designs. Construction costs were available for 183 sites, with a total adjusted investment of USD$22 M and although highly variable the average cost per metre differential head was USD$110,000 (range USD$4500–286,000) per vertical-metre making rock fishways one of the most cost-effective designs available. Two field case-studies provided support for passage of a broad size range (15–410 mm long) of fish at a wide range of flows with hydraulic reliability over considerable design life-spans (i.e., >25 years). The publicly-available rock fishway database forms a platform for sharing technical information to promote more effective designs, contributing to continued global development of rock fishways and conservation of freshwater fish communities.

Deep JKO: Time-implicit particle methods for general nonlinear gradient flows

We develop novel neural network-based implicit particle methods to compute high-dimensional Wasserstein-type gradient flows with linear and nonlinear mobility functions. The main idea is to use the Lagrangian formulation in the Jordan–Kinderlehrer–Otto (JKO) framework, where the velocity field is approximated using a neural network. We leverage the formulations from the neural ordinary differential equation (neural ODE) in the context of continuous normalizing flow for efficient density computation. Additionally, we make use of an explicit recurrence relation for computing derivatives, which greatly streamlines the backpropagation process. Our methodology demonstrates versatility in handling a wide range of gradient flows, accommodating various potential functions and nonlinear mobility scenarios. Extensive experiments demonstrate the efficacy of our approach, including an illustrative example from Bayesian inverse problems. This underscores that our scheme provides a viable alternative solver for the Kalman-Wasserstein gradient flow.

Ignition and combustion behavior of pressure treated wood and wood-plastic composite exposed to glowing firebrand piles: Impact of air flow velocity, firebrand coverage density and pile orientation

Pressure treated wood (PTW) and wood-plastic composite (Trex®) were exposed to glowing firebrand piles in a bench-scale wind tunnel. The air flow velocity was 0.9–2.7 m s−1, the firebrand coverage densities were 0.06 and 0.16 g cm−2, and the pile footprint was 5 × 10 cm2 with either the 10-cm or 5-cm sides perpendicular to the incident air flow. Several types of flaming ignition events were observed including flames attached to the substrate surface in front of the pile (preleading zone ignition), and flames attached to the pile that sometimes spread onto the substrate downstream of the pile (downstream ignition). The most frequent and long-lasting flaming combustion occurred in experiments performed at 2.4–2.7 m s−1 using 0.16 g cm−2 firebrand coverage density piles with 10-cm sides perpendicular to the air flow. Trex® was less prone to preleading zone ignition but was more prone to downstream ignition. Unlike Trex®, PTW exhibited a propensity for sustained smoldering for a wide range of air flows.

An Onshore Deployment of Advanced Dual-Doppler Radar for Wind Energy Applications

Two advanced X-band radars have been developed and deployed by Texas Tech University to provide continuous wind measurements serving project AWAKEN, including the construction of near real-time dual-Doppler synthesized wind fields covering a large 35 km x 35 km analysis domain. This deployment represents the first overland long duration utilization of the technology, which was configured to document a wide range of wind energy relevant flows spanning turbine inflow/wake flow to regional wind flows and wind plant interactions. The overland environment coupled with technology innovation has led to very high data availability yielding a growing archive of measurements documenting diverse atmospheric phenomena including numerous instances of wind plant interaction. Through the first few project months, data availability greater than 90%, 80% and 70% has been assessed at the ranges of 8 km, 16 km, and 25 km, respectively. Robust data availability coupled with fast radar scan speeds and high along beam measurement resolution position advanced Doppler radar technology to broadly contribute to diverse wind energy measurement applications covering domains sizes that far exceed existing industry standard measurement systems.

An artistic perspective on individual space–time flows

ABSTRACT Cartographically, there are now many ways of depicting the spatiotemporal life of human individuals, from flow and animated maps to 3D space-time cubes. However, these scientifically led representations have limited expressive potential for the emotional and inner life of these individuals. Artistic visual forms have been identified as a resource to bring such qualitative communication to and alongside maps. In the ‘Journey as a Flow' project we attempt to represent the geometry and motivation of everyday human motion in relation to various points in the environment and within an environment of other individual flows. We have produced various visual artwork sketches in order to understand the wide range of environmental flows of an individual as well as one's perception of them. We used the space-time cube (i.e. time-geographic aquarium) as a starting point, dictated by the need to create a functional tool in which space and time were both visible, as well as having potential as a 3D tangible object for physical exhibition. This forms the basis for analyses of displacement, interaction and perception. All the modifications of this established geospatial visualisation are inspirations and incorporations from art disciplines. The project outputs therefore include inspirations from cine-plastic art and Escher’s perspective drawings, but the main part of it draws from the Italian renaissance concept of the image conceived as a framed window through which we look at the world. The idea of central perspective has also been used to portray spaces as a flow toward a specific destination. The overall set of representations depict a dynamic version of human lives, while the set of various metaphors deployed drive an artistic interpretation of how some people can perceive (their own / other) flows during their journey. A transformation has therefore occurred from a temporal flow would be conventionally spatial to one that assumes platial properties (i.e. an individually led geography of place).

Analysis of bifurcation, chaotic structures, lump and $ M-W $-shape soliton solutions to $ (2+1) $ complex modified Korteweg-de-Vries system

&lt;abstract&gt;&lt;p&gt;This research focuses on the fascinating exploration of the $ (2+1) $-dimensional complex modified Korteweg-de Vries (CmKdV) system, exhibiting its complex dynamics and solitary wave solutions. This system is a versatile mathematical model that finds applications in various branches of physics, including fluid dynamics, plasma physics, optics, and nonlinear dynamics. Two newly developed methodologies, namely the auxiliary equation (AE) method and the Hirota bilinear (HB) method, are implemented for the construction of novel solitons in various formats. Numerous novel soliton solutions are synthesised in distinct formats, such as dark, bright, singular, periodic, combo, $ W $-shape, mixed trigonometric, exponential, hyperbolic, and rational, based on the proposed methods. Furthermore, we also find some lump solutions, including the periodic cross rational wave, the homoclinic breather (HB) wave solution, the periodic wave solution, the $ M $-shaped rational wave solution, the $ M $-shaped interaction with one kink wave, and the multiwave solution, which are not documented in the literature. In addition, we employ the Galilean transformation to derive the dynamic framework for the presented equation. Our inquiry includes a wide range of topics, including bifurcations, chaotic flows, and other intriguing dynamic properties. Also, for the physical demonstration of the acquired solutions, 3D, 2D, and contour plots are provided. The resulting structure of the acquired results can enrich the nonlinear dynamical behaviors of the given system and may be useful in many domains, such as mathematical physics and fluid dynamics, as well as demonstrate that the approaches used are effective and worthy of validation.&lt;/p&gt;&lt;/abstract&gt;

Coupled effects of variable permeability and adiabatic undulating walls on natural convective flow in a trapezoidal cavity: Finite element analysis

Investigation of hydrothermal characteristics and entropy produced by change in diameter of circular cylinder positioned at the center of trapezoidal enclosure with undulated upper wall is conducted. Natural convection phenomenon is considered along with physical aspects of inclining magnetic field and permeable medium. Envisioning all these factors combined no such study is available which makes current problem novel. So, the premier intends to commence this artifact is to fill the existing gap by comprehensively disclosing the influence of governing transport parameters attained after mathematical modeling in dimensionless format. Entropy phenomenon is analyzed by estimating total entropy and average Bejan number. The numerical solution of modeled mathematical framework is attained by utilizing finite element based open-source software renowned as COMSOL. Wide range of flow concerning parameters are considered for instance, diameter of cylinder (0.10≤D1≤0.20), Prandtl number (0.015≤Pr≤7.00), Rayleigh number (103≤Ra≤105), Darcy number (10-5≤Da≤10-3) and Hartmann number (0≤Ha≤10) while, remaining parameters like angle of inclination (γ) and irreversibility ratio (ω) are fixed at 45° and 10-2 respectively. The influence of these parameters on distributions is interpreted by displaying streamlines and isotherms. After scrutinization of outcomes, it is deduced that average Nusselt number, total entropy and average Bejan number enhances up to 3.49 %, 1.86 % and 2.70 % respectively for situation when diameter of cylinder is increased from 0.10 to 0.20. Furthermore, 28.35 %, 43.06 % and 59.55 % decrement in previously stated quantities is revealed in comparative manner for hydrodynamic (Ha =0) and hydromagnetic (Ha ≠0) cases.

Artificial compressibility method for high-pressure transcritical fluids at low Mach numbers

Supercritical fluids possess unique properties that makes them relevant in various scientific and engineering applications. However, the experimental investigation of these fluids is challenging due to the high pressures involved and their complex thermophysical behavior. To overcome these limitations, computational researchers employ scale-resolving methods, such as direct numerical simulation and large-eddy simulation to study them. Nonetheless, these methods require substantial computational resources, especially in the case of low-Mach-number regimes due to the disparity between acoustic and hydrodynamic/thermal time scales. This work, therefore, addresses this problem by extending the artificial compressibility method to high-pressure transcritical fluids. This method is based on decoupling the thermodynamic and hydrodynamic parts of the pressure field, such that the acoustic time scales can be externally modified without severely impacting the flow physics of the problem. In addition, the method proposed has two key characteristics: (i) the splitting method presents low computational complexity, and (ii) an automatic strategy for selecting the speedup factor of the approach is introduced. The effectiveness of the resulting methodology is demonstrated through comprehensive numerical tests of increasing complexity, showcasing its ability to accurately simulate a wide range of high-pressure transcritical flows including turbulence. The results obtained indicate that the approach proposed can readily lead to computational speedups larger than 10× without significantly compromising the accuracy of the numerical solutions.

A new ghost-cell/level-set method for three-dimensional flows

This study presents the implementation of a tailored ghost cell method in Hydro3D, an open-source large eddy simulation (LES) code for computational fluid dynamics based on the finite difference method. The former model for studying the interaction between an immersed object and the fluid flow is the immersed boundary method (IBM) which has been validated for a wide range of Reynolds number flows. However, it is challenging to ensure no-slip and zero gradient boundary conditions on the surface of an immersed body. In order to deal with this, a new sharp-interface ghost-cell method (GCM) is developed for Hydro3D. The code also employs a level-set method to capture the motion of the air-water interface and solves the spatially filtered Navier-Stokes equations in a Cartesian staggered grid with the fractional step method. Both the new GCM and IBM are compared in a single numerical framework. They are applied to simulate benchmark cases in order to validate the numerical results, which mainly comprise single-phase flow over infinite circular and square cylinders for low- and high-Reynolds number flows along with two-phase dam-break flows with a vertical cylinder, in which a good agreement is obtained with other numerical studies and laboratory experiments.

Can't pass or won't pass: the importance of motivation when quantifying improved connectivity for riverine brown trout Salmo trutta.

Reversing the negative impacts that anthropogenic habitat fragmentation has on animal movement is a key goal in the management of landscapes and conservation of species globally. Accurate assessment of measures to remediate habitat fragmentation, such as fish passage solutions in rivers, are imperative but are particularly challenging for territorial species, which are less likely to leave their existing home range, or populations composed of both migratory and resident individuals (i.e., partial migration). This investigation quantified the movements of translocated (captured upstream of the impediment and released downstream) and non-translocated (captured and released downstream of the impediment) riverine brown trout (Salmo trutta L.), a species known to perform a homing movement, through a fish pass using passive integrated transponder (PIT) telemetry. A significantly higher proportion of translocated fish approached, entered, and passed (on a wider range of flows) compared to non-translocated fish, consistent with the theory that motivation is a key driver in fish pass use. Translocated fish that entered the pass were significantly larger than those that approached but did not enter, presumably due to physiological capability. Translocated fish were a more reliable indicator of the fish passage solution effectiveness than non-translocated fish. Our findings hence imply that many fish passage solutions globally, and potentially measures to remediate habitat fragmentation for other taxa, may have been mistakenly assessed for unmotivated animals. Studying both non-translocated and translocated fish is recommended to provide more accurate and cost-effective fish passage solution assessments.

Evaluation of the Aeroacoustic Sources of a Swirl Diffusor

The acoustic noise generated by air diffusers can have negative impacts on a productive working environment and thus is a considerable limiting factor in ventilation systems. A reliable prediction of sound sources and levels offers the potential to minimise noise emissions in the early design process of air diffusers. In this work, we investigate a commercially available swirl diffuser. For a complete coverage of all flow and acoustic phenomena, the swirl diffuser is only slightly modified and modelled with transient flow simulations. We use large-eddy simulations coupled with the perturbed convective wave equation to model the flow and the aeroacoustic behaviour. The diffuser can be operated over a wide range of volume flows. To limit the computational cost, we investigate the diffuser at three operating points (278, 414 and 549 m3/h). To validate the computed aeroacoustic behaviour we use acoustic measurements. Laser-Doppler-Anemometry measurements are carried out to validate the flow simulation. The transient model is able to predict a sound spectrum and attribute certain features of the spectrum to geometric features of the air diffuser. Furthermore, the flow structures responsible for the sound are determined. These insights can offer guidelines for future designs of comparable air diffusers.