Large Eddy Simulation of Acoustical Sources in a Low Pressure Axial-Flow Fan Encountering Highly Turbulent Inflow

2006 ◽  
Vol 129 (3) ◽  
pp. 263-272 ◽  
Author(s):  
Hauke Reese ◽  
Chisachi Kato ◽  
Thomas H. Carolus
Keyword(s):  
Large Eddy Simulation ◽  
Power Level ◽  
Axial Flow ◽  
Leading Edge ◽  
Sound Power ◽  
Axial Flow Fan ◽  
Eddy Simulation ◽  
Turbulent Inflow ◽  
Large Eddy ◽  
Turbulence Grid

A large eddy simulation (LES) was applied to predict the unsteady flow in a low-speed axial-flow fan assembly subjected to a highly “turbulent” inflow that is generated by a turbulence grid placed upstream of the impeller. The dynamic Smagorinsky model (DSM) was used as the subgrid scale (SGS) model. A streamwise-upwind finite element method (FEM) with second-order accuracy in both time and space was applied as the discretization method together with a multi-frame of reference dynamic overset grid in order to take into account the effects of the blade-wake interactions. Based on a simple algebraic acoustical model for axial flow fans, the radiated sound power was also predicted by using the computed fluctuations in the blade force. The predicted turbulence intensity and its length scale downstream of the turbulence grid quantitatively agree with the experimental data measured by a hot-wire anemometry. The response of the blade to the inflow turbulence is also well predicted by the present LES in terms of the surface pressure fluctuations near the leading edge of the blade and the resulting sound power level. However, as soon as the effects of the turbulent boundary layer on the blades become important, the prediction tends to become inaccurate.

Large Eddy Simulation and Acoustical Analysis for Prediction of Aeroacoustics Noise Radiated From an Axial-Flow Fan

2006 ◽  
Author(s):  
Yoshinobu Yamade ◽  
Chisachi Kato ◽  
Hayato Shimizu ◽  
Takahiro Nishioka
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Unsteady Flow ◽  
Axial Flow ◽  
Rotor Blades ◽  
Coarse Mesh ◽  
Axial Flow Fan ◽  
Eddy Simulation ◽  
Fine Mesh ◽  
Large Eddy

A final objective of this study is to develop a tool to predict aeroacoustics noise radiated from a low-speed fan, and its reduction. Aeroacoustics noise that is radiated from a low-speed axial flow fan, with a six-blades rotor installed in a casing duct, is predicted by an one-way coupled analysis of the computation of the unsteady flow in the ducted fan and computation of the sound radiated to the ambient air. The former is performed by our original code, FrontFlow/blue, which is based on Large Eddy Simulation (LES). The latter is performed by using a commercial code, SYSNOISE, which computes the sound fields in the frequency domain. The following three cases of computations are performed for LES with different flow field configurations and/or grid resolutions: a coarse mesh without the struts located, in the actual fan, upstream of the rotor blades, a fine mesh without the struts, and a coarse mesh with the struts. The first two test cases are intended to investigate the effects of the mesh resolution on the prediction accuracy of the unsteady flow field, especially we intended to capture unsteadiness in turbulent boundary layer (TBL) in the second test case with the computational mesh composed of about 30 millions hexahedral elements. The fine mesh LES successfully reproduced the transition to TBL on the suction surface of the rotor blades and gives better, when compared with the results from the coarse mesh LES, agreements with measurements in terms of Euler’s. The final case is used for providing acoustical input data of the sound source. A reasonable agreement is obtained between the predicted and measured sound pressure level evaluated at 1.5 m upstream of the blade center.

Large Eddy Simulation of Wake-Shear Layer Interactions Over a Multi-Element Aerofoil

2020 ◽  
Author(s):  
Souvik Naskar ◽  
S. Sarkar
Keyword(s):  
Large Eddy Simulation ◽  
Shear Layer ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Suction Surface ◽  
Free Stream Turbulence ◽  
Eddy Simulation ◽  
Large Eddy

Abstract Modern commercial airliners use multi-element aerofoils to enhance take-off and landing performance. Further, multielement aerofoil configurations have been shown to improve the aerodynamic characteristics of wind turbines. In the present study, high resolution Large Eddy Simulation (LES) is used to explore the low Reynolds Number (Re = 0.832 × 104) aerodynamics of a 30P30N multi-element aerofoil at an angle of attack, α = 4°. In the present simulation, wake shed from a leading edge element or slat is found to interact with the separated shear layer developing over the suction surface of the main wing. High receptivity of shear layer via amplification of free-stream turbulence leads to rollup and breakdown, forming a large separation bubble. A transient growth of fluctuations is observed in the first half of the separation bubble, where levels of turbulence becomes maximum near the reattachment and then decay depicting saturation of turbulence. Results of the present LES are found to be in close agreement with the experiment depicting high vortical activity in the outer layer. Some features of the flow field here are similar to those occur due to interactions of passing wake and the separated boundary layer on the suction surface of high lift low pressure turbine blades.

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.

Large Eddy Simulation on the Interactions of Wake and Film-Cooling Near a Leading Edge

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
S. Sarkar ◽  
Harish Babu
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Vortex Pair ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Constant Thickness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Past A Cylinder ◽  
Downward Spiral

The unsteady flow physics due to interactions between a separated shear layer and film cooling jet apart from excitation of periodic passing wake are studied using large eddy simulation (LES). An aerofoil of constant thickness with rounded leading edge induced flow separation, while film cooling jets were injected normal to the crossflow a short distance downstream of the blend point. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case, an infinite row of the model aerofoils). This setup is a simplified representation of rotor-stator interaction in a film cooled gas turbine. The results of numerical simulation are presented to elucidate the formation, convection and breakdown of flow structures associated with the highly anisotropic flow involved in film cooling perturbed by convective wakes. The various vortical structures namely, horseshoe vortex, roller vortex, upright wake vortex, counter rotating vortex pair (CRVP), and downward spiral separation node (DSSN) vortex associated with film cooling are resolved. The effects of wake on the evolution of these structures are then discussed.

scholarly journals Numerical modelling of microburst with Large-Eddy Simulation

2010 ◽  
Vol 10 (10) ◽  
pp. 24345-24370
Author(s):  
V. Anabor ◽  
U. Rizza ◽  
G. A. Degrazia ◽  
E. de Lima Nascimento
Keyword(s):  
Large Eddy Simulation ◽  
Time Scale ◽  
Doppler Radar ◽  
Leading Edge ◽  
Ring Vortex ◽  
Short Time Scale ◽  
Eddy Simulation ◽  
Cloud Models ◽  
Large Eddy ◽  
The Impact

Abstract. An isolated and stationary microburst is simulated using a 3-D time-dependent, high resolution Large-Eddy Simulation (LES) model. The microburst downdraft is initiated by specifying a simplified cooling source at the top of the domain near 2 km. The modelled time scale for this damaging wind (30 m/s) is of order of few min with a spatial scale enclosing a region with 500 m radius around the impact point. These features are comparable with results obtained from full-cloud models. The simulated flow shows the principal features observed by Doppler radar and others observational full-scale downburst events. In particular are observed the expansion of the primary and secondary cores, the presence of the ring vortex at the leading edge of the cool outflow, and finally an accelerating outburst of surface winds. This result evidences the capability of LES to reproduce complexes phenomena like a Microburst and indicates the potential of LES for utilization in atmospheric phenomena situated below the storm scale and above the microscale, which generally involves high velocities in a short time scale.

Interactions of Separation Bubble With Oncoming Wakes by Large-Eddy Simulation

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
S. Sarkar ◽  
Harish Babu ◽  
Jasim Sadique
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Leading Edge ◽  
Constant Thickness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Past A Cylinder ◽  
Rotor Stator Interaction

The unsteady flow physics and heat transfer characteristics due to interactions of periodic passing wakes with a separated boundary layer are studied using large-eddy simulation (LES). A series of airfoils of constant thickness with rounded leading edge are employed to obtain the separated boundary layer. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case, an infinite row of the model airfoils). This setup is a simplified representation of the rotor–stator interaction in turbomachinery. With a uniform inlet, the laminar boundary layer separates near the leading edge, undergoes transition due to amplification of disturbances, becomes turbulent, and finally reattaches forming a separation bubble. In the presence of oncoming wakes, the characteristics of the separated boundary layer have changed and the impinging wakes are found to be the mechanism affecting the reattachment. Phase-averaged results illustrate the periodic behavior of both flow and heat transfer. Large undulations in the phase-averaged skin friction and Nusselt number distributions can be attributed to the excitation of the boundary layer by convective wakes forming coherent vortices, which are being shed and convect downstream. Further, the transition of the separated boundary layer during the wake-induced path is governed by a mechanism that involves the convection of these vortices followed by increased fluctuations, where viscous effect is substantial.

Large Eddy Simulation on the Interactions of Wake and Film-Cooling Near a Leading Edge

2014 ◽  
Author(s):  
Harish Babu ◽  
S. Sarkar
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Vortex Pair ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Constant Thickness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Past A Cylinder ◽  
Rotor Stator Interaction

The unsteady flow physics due to interactions between a separated shear layer and film cooling jet apart from excitation of periodic passing wake are studied using Large Eddy Simulation (LES). An aerofoil of constant thickness with rounded leading edge induced flow separation, while film cooling jets were injected normal to the crossflow a short distance downstream of the blend point. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case, an infinite row of the model aerofoils). This setup is a simplified representation of rotor-stator interaction in a film cooled gas turbine. The results of numerical simulation are presented to elucidate the formation, convection and breakdown of flow structures associated with the highly anisotropic flow involved in film cooling perturbed by convective wakes. The various vortical structures namely, horseshoe vortex, roller vortex, upright wake vortex, counter rotating vortex pair and DSSN vortex associated with film cooling are resolved. The effects of wake on the evolution of these structures are then discussed.

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