Scattering of Plane Waves by a Constriction

2011 ◽  
Author(s):  
E. Alenius ◽  
M. A˚bom ◽  
L. Fuchs
Keyword(s):  
Acoustic Waves ◽  
Plane Waves ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Flow Noise ◽  
Times Series ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Low Frequency Waves ◽  
Good Agreement

Liner scattering of low frequency waves by an orifice plate has been studied using Large Eddy Simulation and an acoustic two-port model. The results have been compared to measurements with good agreement for waves coming from the downstream side. For waves coming from the upstream side the reflection is over-predicted, indicating that not enough of the acoustic energy is converted to vorticity at the upstream edge of the plate. Furthermore, the sensitivity to the amplitude of the acoustic waves has been studied, showing difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the relatively short times series available in LES.

Aeroacoustic Sound Prediction of a Diaphragm by a Hybrid Method

2013 ◽  
Author(s):  
Morteza Bayati ◽  
Mehran Tadjfar
Keyword(s):  
Green Function ◽  
Input Data ◽  
Low Frequency ◽  
Prediction Methods ◽  
Noise Prediction ◽  
Frequency Range ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Mode A ◽  
Good Agreement

Most of the noise prediction methods, which has already been used, only applicable at low frequency range, below the first transverse duct mode. A developed method at this work, which suggested by Schram, avoided many simplification assumptions and is quite powerful for high Helmholtz numbers, i.e. when the turbulence/body interaction region is acoustically non-compact. By using numerical methods and an appropriate Green function, the method is applied to the prediction of sound in a duct obstructed by a diaphragm. The source fluctuations of the flow field are computed by a large-eddy simulation (LES) and are fed to the following acoustical computation as input data. The predicted power spectrum shows a fairly good agreement with a direct noise computation (DNC) results.

scholarly journals Large Eddy Simulation of Periodic Transient Pressure Fluctuation in a Centrifugal Pump Impeller at Low Flow Rate

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 311
Author(s):  
Renfei Kuang ◽  
Xiaoping Chen ◽  
Zhiming Zhang ◽  
Zuchao Zhu ◽  
Yu Li
Keyword(s):  
Large Eddy Simulation ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
Low Frequency ◽  
Pump Impeller ◽  
Eddy Simulation ◽  
Inlet Flow Rate ◽  
Large Eddy ◽  
Centrifugal Pump Impeller

This paper presents a large eddy simulation of a centrifugal pump impeller during a transient condition. The flow rate is sinusoidal and oscillates between 0.25Qd (Qd indicates design load) and 0.75Qd when the rotating speed is maintained. Research shows that in one period, the inlet flow rate will twice reach 0.5Qd, and among the impeller of one moment is a stall state, but the other is a non-stall state. In the process of flow development, the evolution of low-frequency pressure fluctuation shows an obviously sinusoidal form, whose frequency is insensitive to the monitoring position and equals to that of the flow rate. However, inside the impeller, the phase and amplitude in the stall passages lag behind more and are stronger than that in the non-stall passages. Meanwhile, the strongest region of the high-frequency pressure fluctuation appears in the stall passages at the transient rising stage. The second dominant frequency in stall passages is 2.5 times to that in non-stall passages. In addition, similar to the pressure fluctuation, the evolution of the low-frequency head shows a sinusoidal form, whose phase is lagging behind that by one-third of a period in the inlet flow rate.

scholarly journals A Mixed-Fidelity Numerical Study for Fan–Distortion Interaction

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Yunfei Ma ◽  
Jiahuan Cui ◽  
Nagabhushana Rao Vadlamani ◽  
Paul Tucker
Keyword(s):  
Immersed Boundary Method ◽  
Numerical Study ◽  
Immersed Boundary ◽  
Fan Performance ◽  
Inlet Distortion ◽  
Eddy Simulation ◽  
Pressure Distributions ◽  
Large Eddy ◽  
Dynamics Method ◽  
Good Agreement

Inlet distortion often occurs under off-design conditions when a flow separates within an intake and this unsteady phenomenon can seriously impact fan performance. Fan–distortion interaction is a highly unsteady aerodynamic process into which high-fidelity simulations can provide detailed insights. However, due to limitations on the computational resource, the use of an eddy resolving method for a fully resolved fan calculation is currently infeasible within industry. To solve this problem, a mixed-fidelity computational fluid dynamics method is proposed. This method uses the large Eddy simulation (LES) approach to resolve the turbulence associated with separation and the immersed boundary method (IBM) with smeared geometry (IBMSG) to model the fan. The method is validated by providing comparisons against the experiment on the Darmstadt Rotor, which shows a good agreement in terms of total pressure distributions. A detailed investigation is then conducted for a subsonic rotor with an annular beam-generating inlet distortion. A number of studies are performed in order to investigate the fan's influence on the distortions. A comparison to the case without a fan shows that the fan has a significant effect in reducing distortions. Three fan locations are examined which reveal that the fan nearer to the inlet tends to have a higher pressure recovery. Three beams with different heights are also tested to generate various degrees of distortion. The results indicate that the fan can suppress the distortions and that the recovery effect is proportional to the degree of inlet distortion.

Large Eddy Simulation of Laminar and Turbulent Shock/Boundary Layer Interactions in a Transonic Passage

2020 ◽  
Author(s):  
Stephan Priebe ◽  
Daniel Wilkin ◽  
Andy Breeze-Stringfellow ◽  
Giridhar Jothiprasad ◽  
Lawrence C. Cheung
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Low Frequency ◽  
Boundary Layer Separation ◽  
Eddy Simulation ◽  
Turbulent Inflow ◽  
Wide Range ◽  
Large Eddy ◽  
Constant Radius ◽  
Structure Boundary

Abstract Shock/boundary layer interactions (SBLI) are a fundamental fluid mechanics problem relevant in a wide range of applications including transonic rotors in turbomachinery. This paper uses wall-resolved large eddy simulation (LES) to examine the interaction of normal shocks with laminar and turbulent inflow boundary layers in transonic flow. The calculations were performed using GENESIS, a high-order, unstructured LES solver. The geometry created for this study is a transonic passage with a convergent-divergent nozzle that expands the flow to the desired Mach number upstream of the shock and then introduces constant radius curvature to simulate local airfoil camber. The Mach numbers in the divergent section of the transonic passage simulate single stage commercial fan blades. The results predicted with the LES calculations show significant differences between laminar and turbulent SBLI in terms of shock structure, boundary layer separation and transition, and aerodynamic losses. For laminar flow into the shock, significant flow separation and low-frequency unsteadiness occur, while for turbulent flow into the shock, both the boundary layer loss and the low-frequency unsteadiness are reduced.

Heat Transfer Evaluation for a Two-Pass Smooth Wall Channel: Stationary and Rotating Cases

2019 ◽  
Vol 142 (6) ◽  
Author(s):  
Mandana S. Saravani ◽  
Nicholas J. DiPasquale ◽  
Ahmad I. Abbas ◽  
Ryoichi S. Amano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotational Speed ◽  
Numerical Study ◽  
Flow Behavior ◽  
Smooth Wall ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

Abstract This study presents findings on combined effects of Reynolds number and rotational effect for a two-pass channel with a 180-deg turn, numerically and experimentally. To have a better understanding of the flow behavior and to create a baseline for future studies, a smooth wall channel with the square cross section is used in this study. The Reynolds number varies between 6000 and 35,000. Furthermore, by changing the rotational speed, the maximum rotation number of 1.5 is achieved. For the numerical investigation, large eddy simulation (LES) is utilized. Results from the numerical study show a good agreement with the experimental data. From the results, it can be concluded that increasing both Reynolds number and rotational speed is in favor of the heat transfer coefficient enhancement, especially in the turn region.

Noise Generated by a Lifted Flame in a Vitiated Co-Flow

2008 ◽  
Author(s):  
Robert Z. Szasz ◽  
Christophe Duwig ◽  
Laszlo Fuchs
Keyword(s):  
Acoustic Field ◽  
Hybrid Approach ◽  
Low Frequency ◽  
Lifted Flame ◽  
Inhomogeneous Wave Equation ◽  
Large Eddy ◽  
Ignition Region ◽  
Acoustic Sources ◽  
Pod Analysis ◽  
Low Frequency Waves

The acoustic field generated by a lifted flame is studied by a hybrid approach. First, Large Eddy Simulations (LES) are used to compute the flow and the acoustic sources. Next, an inhomogeneous wave equation is solved to obtain the resulting acoustic field. The flow computations show good agreement with experimental data. The dominant acoustic sources are found to be located in the ignition region and at the tip of the flame. The acoustic computations revealed the presence of low-frequency waves radiated in the far-field. The shape of the most energetic acoustic modes are identified by POD analysis to be axial modes.

scholarly journals ICCM2015: A Comparison of RANS and LES Computational Methods in Analyzing Ventilation Flow Through a Room Fitted with a Two-Sided Windcatcher

2017 ◽  
Vol 14 (03) ◽  
pp. 1750021 ◽  
Author(s):  
A. Niktash ◽  
B. P. Huynh
Keyword(s):  
Natural Ventilation ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Interior Space ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
Cfd Method ◽  
Good Agreement

A windcatcher is a structure for providing natural ventilation using wind power; it is usually fitted on the roof of a building to exhaust the inside stale air to the outside and supplies the outside fresh air into the building interior space working by pressure difference between outside and inside of the building. In this paper, the behavior of free wind flow through a three-dimensional room fitted with a centered position two-canal bottom shape windcatcher model is investigated numerically, using a commercial computational fluid dynamics (CFD) software package and LES (Large Eddy Simulation) CFD method. The results have been compared with the obtained results for the same model but using RANS (Reynolds Averaged Navier–Stokes) CFD method. The model with its surrounded space has been considered in both method. It is found that the achieved results for the model from LES method are in good agreement with RANS method’s results for the same model.

scholarly journals Interpolation of LES Cloud Surfaces for Use in Direct Calculations of Entrainment and Detrainment

2011 ◽  
Vol 139 (2) ◽  
pp. 444-456 ◽  
Author(s):  
Jordan T. Dawe ◽  
Philip H. Austin
Keyword(s):  
Numerical Model ◽  
Spatial Scales ◽  
Grid Cell ◽  
Time Step ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Temporal And Spatial ◽  
Les Model ◽  
Direct Calculations ◽  
Good Agreement

Abstract Direct calculations of the entrainment and detrainment of air into and out of clouds require knowledge of the relative velocity difference between the air and the cloud surface. However, a discrete numerical model grid forces the distance moved by a cloud surface over a time step to be either zero or the width of a model grid cell. Here a method for the subgrid interpolation of a cloud surface on a discrete numerical model grid is presented. This method is used to calculate entrainment and detrainment rates for a large-eddy simulation (LES) model, which are compared with rates calculated via the direct flux method of Romps. The comparison shows good agreement between the two methods as long as the model clouds are well resolved by the model grid spacing. This limitation of this technique is offset by the ability to resolve fluxes on much finer temporal and spatial scales, making it suitable for calculating entrainment and detrainment profiles for individual clouds.

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