LES of transitional flows using the approximate deconvolution model

Schlatter, Philipp; Stolz, Steffen; Kleiser, Leonhard

doi:10.1016/j.ijheatfluidflow.2004.02.020

Cited by 137 publications

(88 citation statements)

References 20 publications

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“…The model employs the relaxation term (RT) proposed in the context of the approximate deconvolution model (ADM) by Adams & Stolz (1999). It has been shown by Schlatter, Stolz & Kleiser (2004) that the ADM-RT model is accurate and robust in predicting transitional and turbulent flows with spectral methods. The LES resolution was validate against full DNS checking the location/time of the transition to turbulence.…”

Section: Parametric Analysis In the Nonlinear Regimementioning

confidence: 99%

Transition delay in a boundary layer flow using active control

et al. 2013

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Active linear control is applied to delay the onset of laminar-turbulent transition in the boundary layer over a flat plate. The analysis is carried out by numerical simulations of the nonlinear, transitional regime. A three-dimensional, localized initial condition triggering Tollmien-Schlichting waves of finite amplitude is used to numerically simulate the transition to turbulence. Linear quadratic Gaussian controllers based on reduced-order models of the linearized Navier-Stokes equations are designed, where the wall sensors and the actuators are localized in space. A parametric analysis is carried out in the nonlinear regime, for different disturbance amplitudes, by investigating the effects of the actuation on the flow due to different distributions of the localized actuators along the spanwise direction, different sizes of the actuators and the effort of the controllers. We identify the range of parameters where the controllers are effective and highlight the limits of the device for high amplitudes and strong control action. Despite the fully linear control approach, it is shown that the device is effective in delaying the onset of laminar-turbulent transition in the presence of packets characterized by amplitudes a ≈ 1 % of the free stream velocity at the actuator location. Up to these amplitudes, it is found that a proper choice of the actuators positively affects the performance of the controller. For a transitional case, a ≈ 0.20 %, we show a transition delay of ∆Re x = 3.0 × 10 5 .

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Section: Parametric Analysis In the Nonlinear Regimementioning

confidence: 99%

Transition delay in a boundary layer flow using active control

et al. 2013

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“…LES of the flow are performed to save computational resources. The relaxation term of the approximate deconvolution model [16, accounts for the non-resolved scales.…”

Section: Simulationmentioning

confidence: 99%

Flow-field analysis of anti-kidney vortex film cooling

Gräf

Kleiser

2012

J. Therm. Sci.

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Film cooling is an important measure to enable an increase of the inlet temperature of a gas turbine and, thereby, to improve its overall efficiency. The coolant is ejected through spanwise rows of holes in the blades or endwalls to build up a film shielding the material. The holes often are inclined in the downstream direction and give rise to a kidney vortex. This is a counter-rotating vortex pair, with an upward flow direction between the two vortices, which tends to lift off the surface and to locally feed hot air towards the blade outside the pair. Reversing the rotational sense of the vortices reverses these two drawbacks into advantages. In the considered case, an anti-kidney vortex is generated using two subsequent rows of holes both inclined downstream and yawed spanwise with alternating angles. In a previous study, we performed large-eddy simulations (which focused on the fully turbulent boundary layer) of this anti-kidney vortex film-cooling and compared them to a corresponding physical experiment. The present work analyzes the simulated flow field in detail, beginning in the plenum (inside the blade or endwall) through the holes up to the mixture with the hot boundary layer. To identify the vortical structures found in the mean flow and in the instantaneous flow, we mostly use the λ 2 criterion and the line integral convolution (LIC) technique indicating sectional streamlines. The flow regions (coolant plenum, holes, and boundary layer) are studied subsequently and linked to each other. To track the anti-kidney vortex throughout the boundary layer, we propose two criteria which are based on vorticity and on LIC results. This enables us to associate the jet vortices with the cooling effectiveness at the wall, which is the key feature of film cooling.

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“…Depending on the disturbance magnitude, turbulence may appear at the end of the longer domain. Since we are interested in the onset of turbulence and not in turbulence itself, a relaxation-term model (ADM-RT) is used as subgrid model (Schlatter, Stolz & Kleiser 2004;Schlatter et al 2010): in this way, we do not have to increase the spatial resolution in order to resolve the turbulent scales. This model has shown to be accurate and robust in predicting transitional flows (Schlatter et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Energy efficiency and performance limitations of linear adaptive control for transition delay

2016

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A reactive control technique with localised actuators and sensors is used to delay the transition to turbulence in a flat-plate boundary-layer flow. Through extensive direct numerical simulations, it is shown that an adaptive technique, which computes the control law on-line, is able to significantly reduce skin-friction drag in the presence of random three-dimensional perturbation fields with linear and weakly nonlinear behaviour. An energy budget analysis is performed in order to assess the net energy saving capabilities of the linear control approach. When considering a model of the dielectric-barrier-discharge (DBD) plasma actuator, the energy spent to create appropriate actuation force inside the boundary layer is of the same order as the energy gained from reducing skin-friction drag. With a model of an ideal actuator a net energy gain of three orders of magnitude can be achieved by efficiently damping small-amplitude disturbances upstream. The energy analysis in this study thus provides an upper limit for what we can expect in terms of drag-reduction efficiency for linear control of transition as a means for drag reduction.

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LES of transitional flows using the approximate deconvolution model

Cited by 137 publications

References 20 publications

Transition delay in a boundary layer flow using active control

Transition delay in a boundary layer flow using active control

Flow-field analysis of anti-kidney vortex film cooling

Energy efficiency and performance limitations of linear adaptive control for transition delay

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