The experimental study of the low Mach number and high Reynolds number flow around the gap config... more The experimental study of the low Mach number and high Reynolds number flow around the gap configuration was carried out at TsAGI (Central Aerohydrodynamic Institute, Moscow). Both boundary-layer measurements and acoustic farfield measurements have been made in the experiment. It was found that the farfield acoustic spectra were characterized by a pronounced discrete mode along with the broadband noise.
Detached eddy simulation (DES) is a suitable method for the simulation of the sound radiation of ... more Detached eddy simulation (DES) is a suitable method for the simulation of the sound radiation of turbulent flows, providing access to resolved turbulent scales at minimal computational cost. The near-wall region is solved efficiently by RANS while LES is applied to detached regions of large scale turbulence. The various DES implementations of the Institute of Fluid Mechanics and Engineering Acoustics (ISTA) at the TU-Berlin are described. Simplified academic flow cases are used for the validation of the method and the suitability of the method for complex industrial flow applications is also demonstrated. The method proves robust and reliable for a wide range of applications, ranging from external to internal flows, from bluff bodies with massive separation to the partial resolution of attached boundary layers. Examples of applications to noise emission problems are presented for (i) slat noise, (ii) interaction noise, (iii) jet mixing noise, and (iv) trailing-edge noise. The jet no...
This paper describes a 2-step numerical approach for the prediction of broadband noise from low-s... more This paper describes a 2-step numerical approach for the prediction of broadband noise from low-speed flows with separation and demonstrates its applicability on a tandem square cylinder configuration in close comparison with experimental data. The approach consists of a compressible hybrid RANS/LES nearfield simulation and of a surface integral based extrapolation of the noise emitted into the farfield. It is taylored to turbulent flows at high Reynolds number and low Mach number, which is a flow regime highly relevant for the generation of airframe noise.
ABSTRACT Separation control is an important issue in the physiology of birdflight. Here, the adap... more ABSTRACT Separation control is an important issue in the physiology of birdflight. Here, the adaption of the separation control mechanism by bird feathers to the requirements of engineering applications is described in detail. Self-activated movable flaps similar to artificial bird feathers represent a high-lift system for increasing the maximum lift of airfoils. Their effect on the unsteady flow around a two-dimensional airfoil configuration is investigated by a joint numerical and experimental study. First, attention is paid to the automatic opening and closing mechanism of the flap. Following this, its beneficial effect on lift is investigated for varying incidences and flap configurations. In-depth analysis of experimental and numerical results provides a detailed description of the important phenomena and the effect of self-adjusting flaps on the flow around the airfoil. In the second part of this paper, a contribution is made to verification of the applicability of unsteady Reynolds-averaged approaches using statistical turbulence models for unsteady flows with particular attention to turbulent time scales with comparison to the results of a hybrid simulation based on unsteady Reynolds-averaged Navier-Stokes equations and large-eddy simulation. Finally, flight experiments are described using an aircraft with movable flaps fitted on its laminar wing.
Flow-induced noise represents an increasing problem today, particularly in the vicinity of airpor... more Flow-induced noise represents an increasing problem today, particularly in the vicinity of airports. Comprehensive aircraft noise reduction could primarily be achieved through design changes which mitigate the major noise generation mechanisms. However, such changes require reliable aeroacoustic predictions, which is only possible if appropriate numerical tools are available. These must allow the precise calculation of the sound and mean flow fields as well as the most relevant aerodynamic noise sources. In this work a pressure-based 3D finite volume method, which is already well-established in the area of subsonic flow computation, is further developed in order to enable its application for aeroacoustic large-eddy simulations. The flow state and the range of similarity parameters considered here are chosen to be representative of typical airframe noise. This is mainly caused by separated flow around deployed landing gear and high-lift devices during aircraft takeoff and landing. Th...
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2000
This paper presents an overview of the DES methods implemented at the Institute of Fluid Mechanic... more This paper presents an overview of the DES methods implemented at the Institute of Fluid Mechanics and Engineering Acoustics (ISTA) at the TU-Berlin during the course of the European DESider project. As well as the validation of these methods on the basis of simplified, academic flow cases presented in the first part, their suitability and necessity for complex industrial applications
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2010
ABSTRACT Detached eddy simulation (DES) is shown to be a suitable method for the simulation of th... more ABSTRACT Detached eddy simulation (DES) is shown to be a suitable method for the simulation of the sound generation of turbulent flows, because it provides access to the resolved turbulent scales at minimal computational cost. The near-wall region is solved efficiently by RANS while LES is applied to all regions containing scales important for the noise generation. In addition to the usual LES resolution requirements, for acoustics the smallest of these scales are defined by the highest frequencies of interest. The sound radiation is generally computed by solving an integral over a data surface surrounding the source region outside the turbulent flow. The grid must be fine enough to resolve the sources and the propagation between the sources and the data surface. Examples for the simulation of noise emission problems are presented for the influence of nozzle serrations on jet mixing noise and three airframe noise sources, which are rod-airfoil interaction noise, the noise of high-lift devices, and airfoil self noise.
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2012
ABSTRACT Detached-Eddy Simulation (DES) is a promising method for efficient simulation of broadba... more ABSTRACT Detached-Eddy Simulation (DES) is a promising method for efficient simulation of broadband noise at minimal computational cost. Here, results from a study of broadband noise simulation using state-of-the-art DES methods are presented for a rudimentary landing gear configuration. The DDES and IDDES variants are compared with experiments in incompressible simulations. IDDES shows mild improvement in agreement and some increase in the resolution of high frequencies. An attempt is made to independently verify published results for far-field sound prediction, using a compressible simulation coupled with Ffowcs-Williams/Hawkings (FWH) integration. In contrast to the published results, our results do not provide evidence of unexpectedly strong roles played by the ceiling or by quadrupoles. Our results furthermore predict much lower far-field noise levels than the published results. Good agreement between solid and permeable FWH surfaces is found as long as the permeable surfaces are open downstream.
The experimental study of the low Mach number and high Reynolds number flow around the gap config... more The experimental study of the low Mach number and high Reynolds number flow around the gap configuration was carried out at TsAGI (Central Aerohydrodynamic Institute, Moscow). Both boundary-layer measurements and acoustic farfield measurements have been made in the experiment. It was found that the farfield acoustic spectra were characterized by a pronounced discrete mode along with the broadband noise.
Detached eddy simulation (DES) is a suitable method for the simulation of the sound radiation of ... more Detached eddy simulation (DES) is a suitable method for the simulation of the sound radiation of turbulent flows, providing access to resolved turbulent scales at minimal computational cost. The near-wall region is solved efficiently by RANS while LES is applied to detached regions of large scale turbulence. The various DES implementations of the Institute of Fluid Mechanics and Engineering Acoustics (ISTA) at the TU-Berlin are described. Simplified academic flow cases are used for the validation of the method and the suitability of the method for complex industrial flow applications is also demonstrated. The method proves robust and reliable for a wide range of applications, ranging from external to internal flows, from bluff bodies with massive separation to the partial resolution of attached boundary layers. Examples of applications to noise emission problems are presented for (i) slat noise, (ii) interaction noise, (iii) jet mixing noise, and (iv) trailing-edge noise. The jet no...
This paper describes a 2-step numerical approach for the prediction of broadband noise from low-s... more This paper describes a 2-step numerical approach for the prediction of broadband noise from low-speed flows with separation and demonstrates its applicability on a tandem square cylinder configuration in close comparison with experimental data. The approach consists of a compressible hybrid RANS/LES nearfield simulation and of a surface integral based extrapolation of the noise emitted into the farfield. It is taylored to turbulent flows at high Reynolds number and low Mach number, which is a flow regime highly relevant for the generation of airframe noise.
ABSTRACT Separation control is an important issue in the physiology of birdflight. Here, the adap... more ABSTRACT Separation control is an important issue in the physiology of birdflight. Here, the adaption of the separation control mechanism by bird feathers to the requirements of engineering applications is described in detail. Self-activated movable flaps similar to artificial bird feathers represent a high-lift system for increasing the maximum lift of airfoils. Their effect on the unsteady flow around a two-dimensional airfoil configuration is investigated by a joint numerical and experimental study. First, attention is paid to the automatic opening and closing mechanism of the flap. Following this, its beneficial effect on lift is investigated for varying incidences and flap configurations. In-depth analysis of experimental and numerical results provides a detailed description of the important phenomena and the effect of self-adjusting flaps on the flow around the airfoil. In the second part of this paper, a contribution is made to verification of the applicability of unsteady Reynolds-averaged approaches using statistical turbulence models for unsteady flows with particular attention to turbulent time scales with comparison to the results of a hybrid simulation based on unsteady Reynolds-averaged Navier-Stokes equations and large-eddy simulation. Finally, flight experiments are described using an aircraft with movable flaps fitted on its laminar wing.
Flow-induced noise represents an increasing problem today, particularly in the vicinity of airpor... more Flow-induced noise represents an increasing problem today, particularly in the vicinity of airports. Comprehensive aircraft noise reduction could primarily be achieved through design changes which mitigate the major noise generation mechanisms. However, such changes require reliable aeroacoustic predictions, which is only possible if appropriate numerical tools are available. These must allow the precise calculation of the sound and mean flow fields as well as the most relevant aerodynamic noise sources. In this work a pressure-based 3D finite volume method, which is already well-established in the area of subsonic flow computation, is further developed in order to enable its application for aeroacoustic large-eddy simulations. The flow state and the range of similarity parameters considered here are chosen to be representative of typical airframe noise. This is mainly caused by separated flow around deployed landing gear and high-lift devices during aircraft takeoff and landing. Th...
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2000
This paper presents an overview of the DES methods implemented at the Institute of Fluid Mechanic... more This paper presents an overview of the DES methods implemented at the Institute of Fluid Mechanics and Engineering Acoustics (ISTA) at the TU-Berlin during the course of the European DESider project. As well as the validation of these methods on the basis of simplified, academic flow cases presented in the first part, their suitability and necessity for complex industrial applications
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2010
ABSTRACT Detached eddy simulation (DES) is shown to be a suitable method for the simulation of th... more ABSTRACT Detached eddy simulation (DES) is shown to be a suitable method for the simulation of the sound generation of turbulent flows, because it provides access to the resolved turbulent scales at minimal computational cost. The near-wall region is solved efficiently by RANS while LES is applied to all regions containing scales important for the noise generation. In addition to the usual LES resolution requirements, for acoustics the smallest of these scales are defined by the highest frequencies of interest. The sound radiation is generally computed by solving an integral over a data surface surrounding the source region outside the turbulent flow. The grid must be fine enough to resolve the sources and the propagation between the sources and the data surface. Examples for the simulation of noise emission problems are presented for the influence of nozzle serrations on jet mixing noise and three airframe noise sources, which are rod-airfoil interaction noise, the noise of high-lift devices, and airfoil self noise.
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2012
ABSTRACT Detached-Eddy Simulation (DES) is a promising method for efficient simulation of broadba... more ABSTRACT Detached-Eddy Simulation (DES) is a promising method for efficient simulation of broadband noise at minimal computational cost. Here, results from a study of broadband noise simulation using state-of-the-art DES methods are presented for a rudimentary landing gear configuration. The DDES and IDDES variants are compared with experiments in incompressible simulations. IDDES shows mild improvement in agreement and some increase in the resolution of high frequencies. An attempt is made to independently verify published results for far-field sound prediction, using a compressible simulation coupled with Ffowcs-Williams/Hawkings (FWH) integration. In contrast to the published results, our results do not provide evidence of unexpectedly strong roles played by the ceiling or by quadrupoles. Our results furthermore predict much lower far-field noise levels than the published results. Good agreement between solid and permeable FWH surfaces is found as long as the permeable surfaces are open downstream.
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Papers by Thilo Knacke