Swirl intensity influence on interaction between non-swirling and swirling co-axial jets in a combustor configuration: LES and modelling study S. Šarić, B. Kniesner, P. Altenhöfer, S. Jakirlić and Cam Tropea Fachgebiet Strömungslehre und Aerodynamik, Technische Universität Darmstadt Darmstadt, Germany Dalibor Čavar Fluid Mechanics Sec., Dept. of Mech. Eng., Technical University of Denmark Lyngby, Denmark Branislav Basara Advanced Simulation Technology, AVL List GmbH Graz, Austria 5th Int. Symposium on “Turbulence and Shear Flow Phenomena” Munich, Germany, August 27-29, 2007

Outline Motivation/Objectives Flow Configuration Computational details Results Conclusions

Single tuboannular model combustor “Experimental and numerical investigations of flow and mixing in a swirl combustor” (FG SLA) To systematically investigate the effects of Swirl intensity Mass flow rate ratio (Reynolds number) geometry confinement (in terms of ER) Flue (PIV) Inlet Section (LDA) U/Uf Streamlines coloured by Ma-number

SLA Combustor (flow features) Complex mean strain tensor: mean and secondary shearing, streamline curvature, adverse p.g. effects S=1.0

Flow Configurations Parameter Range Reynolds number (mean flow) Mass flow rate (mean flow) Reynolds number (annular flow) Mass flow rate (annular flow) Swirl intensity The objective: investigate the swirl intensity influence on interaction between the central non-swirling stream and the swirling co-axial jet

Computational Details (inflow generation) Three sets of computations Rec=49530, Rem=23500, S=0.0, 0.6 and 1.0 : Swirling inflow generated computationally by assuming a fictitious pressure gradient in azimuthal direction (LES Dynamic Smagorinsky). Additional forcing of the target U-velocity profile (Pierce 2001): LES-f (Simplified) Swirl generation system computed separately (swirler): LES (DSM) Entire combustor computed (swirler + combustor): LES (SM, Cs=0.1) Separate precursor LES of a fully developed, non-swirling (central) pipe flow corresponding to the experiment (Rem = 23500)

Computational Details (discretization, solution domain) FASTEST 3D FV method; collocated variable arrangement; SIMPLE algorithm, second order accuracy in both space (CDS) and time (Crank-Nicolson); block-structured, body-fitted, non-orthogonal meshes. The solution domain consisting of the flue (Lx=4Df), swirler with annular pipe and central pipe is discretized by a Cartesian grid (NxxNrxNq) comprising about 4.6 Mio. cells in total (192x161x128 cells in the flue, 96x49x128 cells in the swirler and 19x(5x32x32) cells in the end part of the central pipe). The time step chosen ( 6x10-5 or 7.7x10−4 Df/Uf) corresponds to CFL < 0.5 in the largest part of solution domain.

Resolution assessment

RANS computations 800 000 grid cells Lx=6Df AVL SWIFT code (AVL GmbH, Graz, Austria): finite volume discretization technique, arbitrary unstructured, collocated grid arrangement, pressure correction is based on SIMPLE algorithm, the so-called “universal” wall treatment that blends the integration up to the wall with the standard wall functions Popovac and Hanjalic (2007), Basara et al. (2007) 800 000 grid cells Lx=6Df

k-z-f turbulence model k-- f : k-v2- f : A robust ER-EV model Hanjalić, Popovac & Hadziabdić, IJHFF 2004

Annular inlet section: mean axial velocity field (LES) Rec=49530; Rem=23500 S=0.0 and 1.0 S=0.0 S=1.0

Results: Inlet Profiles ( annular section, at x= -0.04m)

Results: mean u and u’v’ profiles in the combustor flue

Results: mean u’u’ and v’v’ profiles in the combustor flue

Swirl intensity influence on the flow: LES predictions of the radial (v) and circumferential (w) velocity

Available experimental and LES data Exp.: Roback & Johnson (1983) LES: Pierce & Moin (1998) ER=2.1 S=0.41 Re=47.500 Flow conditions close to the SLA experiment Measurements of the tangential (circumferential) velocity available

Comparison of the available exp. and LES data

Comparison of the available exp. and LES data

Comparison of the available exp. and LES data

Conclusions The effects of the increasing swirl intensity on the interaction between the outer, swirling stream and the inner, non-swirling flow in the near field of a model combustor was computationally investigated applying both LES and k-ζ−f RANS model. The increasingly swirled annular jet promotes an intensive mixing in the near field of combustor. The overall agreement between simulations and measurements is good. This is particularly the case in the shear layer and the outer, wall-affected flow region. The present predictions exhibit a higher level of agreement with the Roback and Johnson’s experimental results. The simulations return a ring-shaped recirculation zone with positive centerline velocities along entire combustor (uncertainties in the experimental outlet boundary condition? An issue of LES resolution / grid design?)