Duct In Presence Research Articles

Erratum to “The flow and heat transfer performances of magnetic nanofluid in a duct in presence of magnetic fields with different direction”

Erratum to “The flow and heat transfer performances of magnetic nanofluid in a duct in presence of magnetic fields with different direction”

The flow and heat transfer performances of magnetic nanofluid in a duct in presence of magnetic fields with different direction

The flow and heat transfer performances of magnetic nanofluid in a duct in presence of magnetic fields with different direction

On the integration of acoustic phase-gradient metasurfaces in aeronautics

Metamaterials might be one of the breakthrough technologies needed from the aeronautic industry to achieve the more and more challenging targets set by the international authorities, especially about noise emissions. In this article, a theoretical link between Transformation Acoustics and Generalized Snell’s Law, two widely used metamaterial models, is demonstrated analytically and applied to case studies. The relevance of the connection in the aeroacoustic field is discussed along with the consequent computational advantages for numerical simulations. This is exploited to perform a simulation-based design optimization of a phase-graded metasurface acoustic lining of a 2 D duct in presence of flow. Results show promising abilities of the optimized device to modify and control the directivity of the noise emitted from the duct by means of unconventional reflections. The noise reduction in the desired direction is obtained through constructive and destructive interference, with no absorption from the boundaries.

Contrast-Enhanced Endoscopic Ultrasound for Evaluation of Common Bile Duct in Presence of Portal Cavernoma

AbstractEndoscopic ultrasound (EUS) is an excellent imaging modality for the evaluation of common bile duct (CBD) because of its close proximity to the transducer placed in duodenum. However, in the presence of portal cavernoma, identification and proper evaluation of CBD become difficult because of presence of numerous venous collaterals. In these circumstances, the evaluation of CBD is more difficult if it is nondilated. In these difficult situations, contrast-enhanced EUS can provide better and clear images of CBD and therefore seems to be an excellent modality to evaluate nondilated CBD in the presence of portal cavernoma.

Development of air exchanging system for subsonic wind tunnel

The study analyzes main ways of air flow cooling in closed-circuit wind tunnels (subsonic and transonic): subject to air exchange (continuous partial exhaust of warm air and its change for colder outside air) and by means of the use of liquid-coolant stationery heat exchanger. It is shown that additional equipment is not required when applying air exchange to cool the flow and, in general, it can reduce costs of wind tunnel maintenance and, consequently, test prices. Based on an example of subsonic wind tunnel designed in TsAGI the evaluation of gas-dynamic and thermo-dynamic circuit flow properties are evaluated. The study also proposes options of air exchange arrangement for high-power operations at w=160 ms-1 in closed test section provided that the outside air temperature is Tf=20 °C. The paper represents the results of numerical simulation for air flow in the segments of wind tunnel duct in presence of air exchange holes.

Second law analysis for nanofluid turbulent flow inside a circular duct in presence of twisted tape turbulators

Finite volume method is employed to simulate water based nanofluid turbulent flow and entropy generation in a heat exchanger. In order to augment heat transfer rate, twisted tape turbulators insert inside the pipe. Second law analysis are presented for various values of height ratio (BR) and pitch ratio (PR) and Reynolds number (Re). Related formulas for entropy generation and Bejan number are provided. Results indicate that secondary flow increases with increasing number of revolution. Bejan number and total entropy generation augment with augment of pitch ratio. But they decreases with augment of Reynolds number and height ratio.

Thermohydraulic Performance Enhancement Using a Novel Combined V-Shaped Bluff Body Configuration

Heat transfer in a duct in presence of V-shape bluff body configuration has been experimentally examined in the turbulent flow regime up to the Reynolds number of 100000. This work presents a wide experimental study on novel combined V-shaped bluff body configuration in a plain duct at different positions. Isothermal pressure drop tests and heat transfer experiments under uniform heat flux conditions have been carried out. The Reynolds number ranges from 100-100000. The results indicate that in presence of V-shaped bluff body, heat transfer in the duct is increased by around 5%-15%. The increase in heat transfer is related to the eddy formation downstream of the V-shaped bluff body. Heat transfer augmentation and friction loss increased with combined effect of V-shaped bluff body configuration. Experimental results indicate that the use of V-shaped bluff body the duct can prominently increase the heat transfer performance.

Experimental and computational multi-port characterization of a circular orifice plate

The generation and scattering behavior of fluid machines in duct systems is of great interest to minimize sound emission, for instance of air condition systems. Such systems may be described as linear, time-invariant multi-port networks containing passive elements, that scatter existing sound fields and active elements, that emit noise themselves. The aim of any multi-port analysis is to determine the direction-dependent transmission and reflection coefficients for the propagating wave modes and the sound generation. This parameters may be ascertained either numerically or experimentally. In a first step, external sound fields dominating the source are applied to determine the system scattering. In a second step, the source strength can be computed. Once these characteristic data are determined for all elements of interest, the sound scattering and emission of every considerable combination of multi-ports can be calculated easily. This paper shows an experimental study as well as a numerical approach to determine both, the passive and the active characterization of an orifice plate in a circular duct in presence of higher order acoustic modes. An enhanced measurement procedure is presented, and the results of this procedure are compared with data extracted from a full compressible DDES flow-computation.

Mathematical modeling of time-harmonic aeroacoustics with a generalized impedance boundary condition

We study the time-harmonic acoustic scattering in a duct in presence of a flow and of a discontinuous impedance boundary condition. Unlike a continuous impedance, a discontinuous one leads to still open modeling questions, as in particular the singularity of the solution at the abrupt transition and the choice of the right unknown to formulate the scattering problem. To address these questions we propose a mathematical approach based on variational formulations set in weighted Sobolev spaces. Considering the discontinuous impedance as the limit of a continuous boundary condition, we prove that only the problem formulated in terms of the velocity potential converges to a well-posed problem. Moreover we identify the limit problem and determine some Kutta-like condition satisfied by the velocity: its convective derivative must vanish at the ends of the impedance area. Finally we justify why it is not possible to define limit problems for the pressure and the displacement. Numerical examples illustrate the convergence process.

Haar wavelet approximation for magnetohydrodynamic flow equations

This study proposes Haar wavelet (HW) approximation method for solving magnetohydrodynamic flow equations in a rectangular duct in presence of transverse external oblique magnetic field. The method is based on approximating the truncated double Haar wavelets series. Numerical solution of velocity and induced magnetic field is obtained for steady-state, fully developed, incompressible flow for a conducting fluid inside the duct. The calculations show that the accuracy of the Haar wavelet solutions is quite good even in the case of a small number of grid points. The HW approximation method may be used in a wide variety of high-order linear partial differential equations. Application of the HW approximation method showed that it is reliable, simple, fast, least computation at costs and flexible.

Setting up an experimental apparatus for the study of multimodal acoustic propagation with turbulent mean flow

An experiment has been set up to study multimodal acoustic propagation inside a cylindrical duct in presence of a turbulent mean flow. This paper describes the preliminary work which has been found necessary for assembling the experiment together with first measurement results. In order to set up this experimental facility, a high level acoustic source was developed to generate higher propagating modes in the presence of mean flow. A microphonic antenna was designed for detecting the propagating modes. LDV measurements were performed and synchronous detection was used to extract both the mean flow and the acoustic components of the particle velocity. Results of aeraulic measurements are presented. Then, results of acoustic velocity measurements are compared to results obtained from the microphonic antenna.

Active control of multimodal tonal noise propagated in circular duct with axial subsonic mean flow until M=0.3

As new generation of aircraft engine with lower blade passing frequency appeared in the 1990's, the fan tones radiated from the inlets had become one of the dominant source of sound. Efforts have then been made to develop active noise control. Encouraging results have been obtained but the physical limitation of the fan tones reduction have not been clearly determined, owing mainly to the complexity of the experimental rigs. This paper present an experimental investigation of the control of multimodal tonal noise propagated in circular duct in presence of a mean flow (M⩽0.3). A laboratory wind tunnel has been implemented for this purpose. Two limiting factors for the sound reduction are underlined: (i) the degradation of the secondary transfer matrix conditioning as the number of propagating modes increases in the duct and (ii) the degradation of the hypothesis of the time-invariance of the system to control as the flow velocity is increased. The effect of those limiting factors on the control efficiency are evaluated.

Active noise control in ducts in presence of standing waves. Its influence on feedback effect

Much of the theoretical and experimental work which has been carried out in the area of active noise control in ducts has neglected the fact that a standing wave is formed in them. A feedforward strategy of control is the most widely used in ducts. Nevertheless, it presents a feedback problem, which can make the system unstable by corrupting the reference signal. Although there are some different solutions to this effect, most of them need special arrangements or algorithms. A model, which demonstates that the acoustic field in the duct is formed by standing waves before and after the active control, is developed and from it, the optimal location of the secondary source to avoid feedback is derived. This result is experimentally validated for a pure tone noise in a duct, and then applied to attenuate fan noise propagating in the same duct. In addition, experimental work has provided some extra information about the location of the error microphone and the usefulness of its signal to evaluate the active noise control system performance.