Björn Greschner

Assessment Of CFD Broadband Noise Predictions On A Rod-Airfoil Benchmark Computation

This paper presents a selection of acoustic far field, unsteady aerodynamic and mean flow results obtained from a variety of unsteady codes on a low Mach rod-airfoil test case. These codes are all applicable to complex geometries such as encountered in turbo engines. Therefore the present computations can be regarded as an evaluation of their capability to predict turbomachinery broadband noise. This quite unique benchmarking work of turbomachinery noise prediction tools has mainly been achieved within the framework of the European Project PROBAND, but some of the results where also obtained by an academic cooperation with a Korean partner.

Measurements and wall Modeled LES Simulation of Trailing Edge Noise Caused by a Turbulent Boundary Layer

A successful comparison between CFD-CAA and measurements of trailing edge noise is shown for a highly loaded and cambered NACA 5510 airfoil at a chord based Reynolds number of aprox. 1 million placed in a quiet low Mach number flow. The simulation is based on a new variant of the DES - the Improved Delayed Detached Eddy Simulation (IDDES). The flow is fully attached to the airfoil and therefore only the small turbulent boundary structures that interact with the trailing edge generate significant broadband noise in the far field. The IDDES approach is designed to extend the LES region of the original DES approach (hybrid RANS/LES) from Spalart et. al. (1997) to the turbulent boundary layer, as proposed first by Travin et. al. in 2006. The non-zonal blending occures therefore inside the boundary layer - the RANS model acts as a wall model for the LES. The actual work shows the capabilities of this novel approach for the simulation of broadband noise for attached flows. The simulation is compared to measurements from the EC Lyon including PIV and LDA data around the airfoil and unsteady on-wall pressure measurements near the trailing edge. Far field computations are carried out by applying the Ffowcs–Williams and Hawkings analogy to the unsteady wall pressure field and compared to acoustic measurements as well as to a far field prediction based on a trailing edge noise model that is applied to the experimental aerodynamic pressure field.

Demonstration of Improved DES Methods for Generic and Industrial Applications

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 is demonstrated using results from other research projects. The methods prove 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.

Wall Modeled LES simulation of Rotor-Stator-Cascade Broadband Noise

Broadband noise generated by a fan (DLR Berlin Fan Rig) is studied numerically using a novel variant of the DES the Improved Delayed Detached Eddy Simulation (IDDES). The full rotating geometry is simpli ed to an rotor-stator-cascade to analyse in detail the rotor and stator selfnoise and the stator interaction noise. The reference DLR Fan Rig has a rotor blade count of 24 with 30 stator vanes. The rotational tip Mach number is M = 0:220 at nominal loading. The IDDES approach is designed to extend the LES region of the original DES approach (hybrid RANS/LES) from Spalart et. al. (1997) to the turbulent boundary layer, as proposed rst by Travin et. al. in 2006. The non-zonal blending occures therefore inside the boundary layer the RANS model acts as a wall model for the LES. The actual work shows the capabilities of this novel approach for the simulation of broadband noise in turbo machines.

Numerical Simulation of Jet Mixing Noise Associated with Engine Exhausts

In this article the work conducted at ISTA and LMFA during the French/German research project Noise Generation in Turbulent Flows is presented. The hybrid approach applied for the noise prediction at ISTA consists of a flow simulation which is coupled to the acoustic analogy of Ffowcs-Williams& Hawkings including predictions based on volume sources. The turbulence modelling approach used in the flow simulations is the Detached-Eddy Simulation as well as the Large- Eddy Simulation. Along with details on the numerical method and the turbulence modelling approach, results from compressible, three-dimensional flow simulations and their acoustic predictions are presented for the rod-airfoil configuration which acts as a simple broadband noise emitter. Additionally, results for a single-stream jet and for a coplanar, coaxial, unheated jet flow are presented. The results of the Detached-Eddy Simulation of the latter case are compared with those of a Large- Eddy Simulation of the same configuration.

Turbulence Modelling Effects on Tandem Cylinder Interaction Flow and Analysis of Installation Effects on Broadband Noise Using Chimera Technique

The NASA tandem cylinder benchmark case (L/D = 3.7) is studied numerically using novel variants of DES the Delayed Detached Eddy Simulation (DDES) and the Improved Delayed Deteched Eddy Simulation (IDDES). The ow Mach number is 0.1285 and the Reynolds number is set to 166.000 to match th corresponding experiments at the NASA Langley Research Center (Jenkins et al., Lockard et al.). Incompressible simulations are carried out on a mandatory grid from the EC ATAAC project with approx. 9.5 million cells with a spanwise extent of 3.0D and ow normal domain extent of approx. 17.8D with symmetry boundary condition to mimic the closed experimental test section. In a second step a compressible IDDES simulation is done to evaluate the broadband noise of the con guration. Measurements are available from the QFF open jet facility. To capture the installation e ects a combined grid of above mentioned cylinder core grid and a single stream jet grid is used. The communication between the grids is done by an overset chimera technique. The noise in the far eld is calculated by a standard FW-H method. The IDDES approach is designed to extend the LES region of the original DES approach (hybrid RANS/LES) from Spalart et. al. (1997) to the turbulent boundary layer, as proposed rst by Travin et. al. in 2006. The non-zonal blending occures therefore inside the boundary layer the RANS model acts as a wall model for the LES. The comparison of the simulations show the improvement of the results by using a IDDES.

Advanced DES Methods and Their Application to Aeroacoustics

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.

Simulation of Rotor Tip Leakage Vortex Broadband Noise using IDDES

Broadband noise generated by a fan is studied numerically using a novel variant of the DES the Improved Delayed Detached Eddy Simulation (IDDES). The IDDES is used together with the Chimera grid overset technique for the independent griding of the rotor, stator and channel and a highly parallel sliding mesh interface suitable for huge simulations. The reference experiment is the DLR Fan Rig within the EC founded project FLOCON. It has a rotor blade count of 24 with 32 stator vanes. The rotational tip Mach number is M = 0.220 at nominal loading with a rotor gap height of 2.4 mm. The objective of the present investigation is to directly simulate the fan rig tip leakage vortex broadband noise using the IDDES. The LES focus region is the tip area including the boundary layer at the casing wall downstream towards the stator vanes. In the remaining domain we use coarser grids suitable for URANS. To capture the effect of the interaction between the rotor blades and stator vanes, a full periodic setup with 3 rotor blades and 4 stator vanes is investigated with the total number of 55 million cells on 600 CPUs. The IDDES approach is designed to extend the LES region of the original DES approach (hybrid RANS/LES) from Spalart et. al. (1997) to the turbulent boundary layer, as proposed first by Travin et. al. in 2006. The non-zonal blending occures therefore inside the boundary layer the RANS model acts as a wall model for the LES. The actual work shows the capabilities of this novel approach for the simulation of broadband noise in turbomachines.