scholarly journals High-frequency wavepackets in turbulent jets

2017 ◽  
Vol 830 ◽  
Author(s):  
Kenzo Sasaki ◽  
André V. G. Cavalieri ◽  
Peter Jordan ◽  
Oliver T. Schmidt ◽  
Tim Colonius ◽  
...  
Keyword(s):  
High Frequency ◽  
Turbulent Jets ◽  
Initial Growth ◽  
Mean Flow ◽  
Flow Equations ◽  
Eddy Simulation ◽  
Linear Waves ◽  
Large Eddy ◽  
Homogeneous Linear ◽  
Good Agreement

Wavepackets obtained as solutions of the flow equations linearised around the mean flow have been shown in recent work to yield good agreement, in terms of amplitude and phase, with those educed from turbulent jets. Compelling agreement has been demonstrated, for the axisymmetric and first helical mode, up to Strouhal numbers close to unity. We here extend the range of validity of wavepacket models to Strouhal number $St=4.0$ and azimuthal wavenumber $m=4$ by comparing solutions of the parabolised stability equations with a well-validated large-eddy simulation of a Mach 0.9 turbulent jet. The results show that the near-nozzle dynamics can be correctly described by the homogeneous linear model, the initial growth rates being accurately predicted for the entire range of frequencies and azimuthal wavenumbers considered. Similarly to the lower-frequency wavepackets reported prior to this work, the high-frequency linear waves deviate from the data downstream of their stabilisation locations, which move progressively upstream as the frequency increases.

scholarly journals Large-eddy simulation of twin impinging jets in cross-flow

2007 ◽  
Vol 111 (1117) ◽  
pp. 195-206 ◽  
Author(s):  
Q. Li ◽  
G. J. Page ◽  
J. J. McGuirk
Keyword(s):  
Large Eddy Simulation ◽  
Cross Flow ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Scale Model ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Suitable Tool ◽  
Large Eddy ◽  
Good Agreement

The flow-field beneath a jet-borne vertical landing aircraft is highly complex and unsteady. large-eddy simulation is a suitable tool to predict both the mean flow and unsteady fluctuations. This work aims to evaluate the suitability of LES by applying it to two multiple jet impingement problems: the first is a simple twin impinging jet in cross-flow, while the second includes a circular intake. The numerical method uses a compressible solver on a mixed element unstructured mesh. The smoothing terms in the spatial flux are kept small by the use of a monitor function sensitive to vorticity and divergence. The WALE subgrid scale model is utilised. The simpler jet impingement case shows good agreement with experiment for mean velocity and normal stresses. Analysis of time histories in the jet shear layer and near impingement gives a dominant frequency at a Strouhal number of 0·1, somewhat lower than normally observed in free jets. The jet impingement case with an intake also gives good agreement with experimental velocity measurements, although the expansion of the grid ahead of the jets does reduce the accuracy in this region. Turbulent eddies are observed entering the intake with significant swirl. This is in qualitative agreement with experimental visualisation. The results show that LES could be a suitable tool when applied to multiple jet impingement with realistic aircraft geometry.

RANS and Large Eddy Simulation of Internal Combustion Engine Flows—A Comparative Study

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Xiaofeng Yang ◽  
Saurabh Gupta ◽  
Tang-Wei Kuo ◽  
Venkatesh Gopalakrishnan
Keyword(s):  
Large Eddy Simulation ◽  
High Speed ◽  
Combustion Engine ◽  
Flow Analysis ◽  
Partial Geometry ◽  
Computational Domain ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Simulations

A comparative cold flow analysis between Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) cycle-averaged velocity and turbulence predictions is carried out for a single cylinder engine with a transparent combustion chamber (TCC) under motored conditions using high-speed particle image velocimetry (PIV) measurements as the reference data. Simulations are done using a commercial computationally fluid dynamics (CFD) code CONVERGE with the implementation of standard k-ε and RNG k-ε turbulent models for RANS and a one-equation eddy viscosity model for LES. The following aspects are analyzed in this study: The effects of computational domain geometry (with or without intake and exhaust plenums) on mean flow and turbulence predictions for both LES and RANS simulations. And comparison of LES versus RANS simulations in terms of their capability to predict mean flow and turbulence. Both RANS and LES full and partial geometry simulations are able to capture the overall mean flow trends qualitatively; but the intake jet structure, velocity magnitudes, turbulence magnitudes, and its distribution are more accurately predicted by LES full geometry simulations. The guideline therefore for CFD engineers is that RANS partial geometry simulations (computationally least expensive) with a RNG k-ε turbulent model and one cycle or more are good enough for capturing overall qualitative flow trends for the engineering applications. However, if one is interested in getting reasonably accurate estimates of velocity magnitudes, flow structures, turbulence magnitudes, and its distribution, they must resort to LES simulations. Furthermore, to get the most accurate turbulence distributions, one must consider running LES full geometry simulations.

scholarly journals Stability and Sensitivity Analysis of Hydrodynamic Instabilities in Industrial Swirled Injection Systems

2017 ◽  
Author(s):  
Thomas L. Kaiser ◽  
Thierry Poinsot ◽  
Kilian Oberleithner
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Vortex Core ◽  
Large Eddy Simulations ◽  
Mode Shapes ◽  
Mean Flow ◽  
Precessing Vortex Core ◽  
Large Eddy ◽  
Good Agreement

The hydrodynamic instability in an industrial, two-staged, counter-rotative, swirled injector of highly complex geometry is under investigation. Large eddy simulations show that the complicated and strongly nonparallel flow field in the injector is superimposed by a strong precessing vortex core. Mean flow fields of large eddy simulations, validated by experimental particle image velocimetry measurements are used as input for both local and global linear stability analysis. It is shown that the origin of the instability is located at the exit plane of the primary injector. Mode shapes of both global and local linear stability analysis are compared to a dynamic mode decomposition based on large eddy simulation snapshots, showing good agreement. The estimated frequencies for the instability are in good agreement with both the experiment and the simulation. Furthermore, the adjoint mode shapes retrieved by the global approach are used to find the best location for periodic forcing in order to control the precessing vortex core.

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.

Loss Predictions in the High-Pressure Film-Cooled Turbine Vane of the FACTOR Project by Mean of Wall-Modeled Large Eddy Simulation

2020 ◽  
Author(s):  
Mael Harnieh ◽  
Nicolas Odier ◽  
Jérôme Dombard ◽  
Florent Duchaine ◽  
Laurent Gicquel
Keyword(s):  
Spatial Distribution ◽  
Large Eddy Simulation ◽  
Film Cooling ◽  
Total Pressure ◽  
Mean Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbine Vane

Abstract The use of numerical simulations to design and optimize turbine vane cooling requires precise prediction of the fluid mechanics and film cooling effectiveness. This results in the need to numerically identify and assess the various origins of the losses taking place in such systems and if possible in engine representative conditions. Large-Eddy Simulation (LES) has shown recently its ability to predict turbomachinery flows in well mastered academic cases such as compressor or turbine cascades. When it comes to industrial representative configurations, the geometrical complexities, high Reynolds and Mach numbers as well as boundary condition setup lead to an important increase of CPU cost of the simulations. To evaluate the capacity of LES to predict film cooling effectiveness as well as to investigate the loss generation mechanisms in a turbine vane in engine representative conditions, a wall-modeled LES of the FACTOR film-cooled nozzle is performed. After the comparison of integrated values to validate the operating point of the vanes, the mean flow structure is investigated. In the coolant film, a strong turbulent mixing process between coolant and hot flows is observed. As a result, the spatial distribution of time-averaged vane surface temperature is highly heterogeneous. Comparisons with the experiment show that the LES prediction fairly reproduces the spatial distribution of the adiabatic film effectiveness. The loss generation in the configuration is then investigated. To do so, two methodologies, i.e, performing balance of total pressure in the vanes wakes as mainly used in the literature and Second Law Analysis (SLA) are evaluated. Balance of total pressure without the contribution of thermal effects only highlights the losses generated by the wakes and secondary flows. To overcome this limitation, SLA is adopted by investigating loss maps. Thanks to this approach, mixing losses are shown to dominate in the coolant film while aerodynamic losses dominate in the coolant pipe region.

scholarly journals Flow visualization using momentum and energy transport tubes and applications to turbulent flow in wind farms

2013 ◽  
Vol 715 ◽  
pp. 335-358 ◽  
Author(s):  
Johan Meyers ◽  
Charles Meneveau
Keyword(s):  
Turbulent Flow ◽  
Flow Visualization ◽  
Energy Transport ◽  
Three Dimensional ◽  
Wind Farms ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Using Data ◽  
Large Wind

AbstractAs a generalization of the mass–flux based classical stream tube, the concept of momentum and energy transport tubes is discussed as a flow visualization tool. These transport tubes have the property that no fluxes of momentum or energy exist over their respective tube mantles. As an example application using data from large eddy simulation, such tubes are visualized for the mean-flow structure of turbulent flow in large wind farms, in fully developed wind-turbine-array boundary layers. The three-dimensional organization of energy transport tubes changes considerably when turbine spacings are varied, enabling the visualization of the path taken by the kinetic energy flux that is ultimately available at any given turbine within the array.

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