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Open AccessArticle

Hybrid Computation of the Aerodynamic Noise Radiated by the Wake of a Subsonic Cylinder

by Benet Eiximeno, Carlos Tur-Mongé, Oriol Lehmkuhl and Ivette Rodríguez

Fluids 2023, 8(8), 236; https://doi.org/10.3390/fluids8080236 - 21 Aug 2023

Cited by 4 | Viewed by 2528

The noise radiated by the flow around a cylinder in the subcritical regime at

R e_{D} = 1 \times 10^{4}

and at a subsonic Mach number of

M = 0.5

is here studied. The aerodynamic sound radiated by a cylinder has [...] Read more.

The noise radiated by the flow around a cylinder in the subcritical regime at

R e_{D} = 1 \times 10^{4}

and at a subsonic Mach number of

M = 0.5

is here studied. The aerodynamic sound radiated by a cylinder has been studied with a wide range of Reynolds numbers, but there are no studies about how the Mach number affects the acoustic field in the subsonic regime. The flow field is resolved by means of large-eddy simulations of the compressible Navier–Stokes equations. For the study of the noise propagation, formulation 1C of the Ffowcs Williams–Hawkings analogy is used. The fluid flow results show good agreement when comparing the surface pressure coefficient, the recirculation length, the vortex shedding frequency and the force coefficients against other studies performed under similar conditions. The dynamic mode decomposition of the pressure fluctuations is used to relate them with the far-field noise. It is shown that, in contrast to what happens for low Mach numbers, quadrupoles have a significant impact mainly in the observers located in the streamwise direction. This effect leads to a global monopole directivity pattern as the shear fluctuations compensate for the lower value of the aeolian tone away from the cross-stream direction. Full article

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23 pages, 9649 KB

Open AccessArticle

Fineness Ratio Effects on the Flow Past an Axisymmetric Body at High Incidence

by José Jiménez-Varona and Gabriel Liaño

Aerospace 2023, 10(5), 432; https://doi.org/10.3390/aerospace10050432 - 4 May 2023

Cited by 1 | Viewed by 2654

Abstract

The flow past an axisymmetric body at a sufficiently high angle of attack becomes asymmetric and unsteady. Several authors identified three different flow regions for bodies of large fineness ratio at low subsonic flow and high incidence: a steady region in the forebody and two unsteady regions in the rear body. Unsteady Reynolds Averaged Navier–Stokes (URANS) codes with eddy viscosity turbulence models or Reynolds stress turbulence models fail to capture the unsteady flow region. These methods are overly dissipative and resolve only frequencies far lower than turbulent fluctuations. Scale-Adaptive-Simulation (SAS) provides an alternative method to afford the problem of these massively separated flows at high Reynolds numbers without addressing the problem to Large Eddy Simulation (LES). This paper applies SAS to study the effect of slenderness on the flow. The numerical solutions show that the flow becomes more unstable as the fineness ratio increases, and the three flow regions are clearly recognizable. For low fineness ratios, only one of the two unsteady regions is visible. The good agreement between the sectional forces and pressure coefficients with their corresponding experimental data for an ogive-cylinder configuration allows an analysis of the flow structure with a fair degree of confidence. Full article

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12 pages, 3476 KB

Open AccessArticle

Numerical Study of the Influence of the Geometrical Irregularities on Bodies of Revolution at High Angles of Attack

by José Jiménez-Varona and Gabriel Liaño

Computation 2022, 10(10), 173; https://doi.org/10.3390/computation10100173 - 28 Sep 2022

Viewed by 2225

Abstract

The flow at high angles of attack over axisymmetric configurations is not symmetric. The mechanism that triggers the asymmetry may be a combination of a global or hydrodynamic instability (temporal instability) combined with a convective instability (spatial instability) due to microscopic irregularities of the configuration. Poor repeatability of experiments and large differences in the global forces have been obtained with very small changes of the nose tip. In order to study theoretically this phenomenon, numerical simulations have been conducted for an ogive-cylinder configuration at subsonic flow and high angle of attack. For the numerical prediction of the flow about a missile type configuration, an assessment of the effect of structured and unstructured meshes is very important. How the body surface is modelled is very relevant; especially the tip zone of the body. Either configuration resembles a smooth or a rough model. The effect of the turbulence models is also decisive. The analysis has led to the conclusion that only Reynolds stress turbulence models (RSM) combined with Scale Adaptive Simulation (SAS), are the appropriate theoretical tools for the characterization of this flow. The geometrical similarity is very important. There is a roll or orientation angle effect for the unstructured grid, while the structured grid presents a bi-stable solution, one mirror of each other. Full article

(This article belongs to the Special Issue Selected Papers from the 10th International Conference from Scientific Computing to Computational Engineering (IC-SCCE 2022))

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15 pages, 8969 KB

Open AccessArticle

An Ultra-Fast TSP on a CNT Heating Layer for Unsteady Temperature and Heat Flux Measurements in Subsonic Flows

by Martin Bitter, Michael Hilfer, Tobias Schubert, Christian Klein and Reinhard Niehuis

Sensors 2022, 22(2), 657; https://doi.org/10.3390/s22020657 - 15 Jan 2022

Cited by 12 | Viewed by 3025

Abstract

In this paper, the authors demonstrate the application of a modified Ru(phen)-based temperature-sensitive paint which was originally developed for the evaluation of unsteady aero-thermodynamic phenomena in high Mach number but short duration experiments. In the present work, the modified TSP with a temperature sensitivity of up to −5.6%/K was applied in a low Mach number long-duration test case in a low-pressure environment. For the demonstration of the paint’s performance, a flat plate with a mounted cylinder was set up in the High-Speed Cascade Wind Tunnel (HGK). The test case was designed to generate vortex shedding frequencies up to 4300 Hz which were sampled using a high-speed camera at 40 kHz frame rate to resolve unsteady surface temperature fields for potential heat-transfer estimations. The experiments were carried out at reduced ambient pressure of

p_{\infty}

= 13.8 kPa for three inflow Mach numbers being

M a_{\infty} = [0.3; 0.5; 0.7]

. In order to enable the resolution of very low temperature fluctuations down to the noise floor of

10^{- 5}

K with high spatial and temporal resolution, the flat plate model was equipped with a sprayable carbon nanotube (CNT) heating layer. This constellation, together with the thermal sensors incorporated in the model, allowed for the calculation of a quasi-heat-transfer coefficient from the surface temperature fields. Besides the results of the experiments, the paper highlights the properties of the modified TSP as well as the methodology. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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22 pages, 3193 KB

Open AccessReview

Passive Control of Base Pressure: A Review

by Ambareen Khan, Parvathy Rajendran and Junior Sarjit Singh Sidhu

Appl. Sci. 2021, 11(3), 1334; https://doi.org/10.3390/app11031334 - 2 Feb 2021

Cited by 20 | Viewed by 6353

Abstract

In the present world, passive control finds application in various areas like flow over blunt projectiles, missiles, supersonic parallel diffusers (for cruise correction), the engine of jets, static testbeds of rockets, the ports of internal combustion engines, vernier rockets, and single expansion ramp nozzle (SERN) rockets. In this review, various passive control techniques to control the base pressure and regulate the drag force are discussed. In the study, papers ranging from subsonic, sonic, and supersonic flow are discussed. Different types of passive control management techniques like cavity, ribs, dimple, static cylinder, spikes, etc., are discussed in this review article. This study found that the passive control device can control the base pressure, resulting in an enhancement in the base pressure and reducing the base drag. Also, passive control is very efficient whenever there is a favorable pressure gradient at the nozzle exit. Full article

(This article belongs to the Special Issue New Trends in Applied Aerodynamics)

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