Effects of boundary conditions on vortex breakdown in compressible swirling jet flow simulations

Luginsland, Tobias; Kleiser, Leonhard

doi:10.1016/j.compfluid.2014.12.012

Cited by 3 publications

(4 citation statements)

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“…A grid resolution study is documented in Luginsland and Kleiser [26], providing evidence of the convergence of mean flow results. The time-step is chosen as t = 0.002 according to a Courant-Friedrichs-Lewy criterion [24].…”

Section: Where Rmentioning

confidence: 99%

“…At the nozzle wall three velocities and the temperature are prescribed. The setup of boundary conditions as well as the initialization follows the recommendations given in [26] and is discussed in more detail in [22].…”

Section: Where Rmentioning

confidence: 99%

“…The nozzle at rest follows Billant et al [5] and Oberleithner et al [4], who used either guiding vanes or a rotating honeycomb for swirl generation. For both configurations, we define inflow boundary conditions for the pressure, p, and the density, ρ, by integrating the radial momentum equation and using the equation of state for an ideal gas, γ Ma 2 p = ρT , assuming a uniform temperature distribution T (r) = 1 [18,26]:…”

Section: Setup Differences For the Rotating Nozzle And The Nozzle At mentioning

confidence: 99%

“…We use a numerical framework [22,25,19,26,24], which allows for a precise study of the effects of the nozzle configuration on the flow field due to high-order methods in time and space. Our aim is to provide insight into the instability mechanisms inherently connected to the nozzle either rotating with the mean flow or kept at rest.…”

Section: Introductionmentioning

confidence: 99%

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Impact of rotating and fixed nozzles on vortex breakdown in compressible swirling jet flows

Luginsland

Gallaire

Kleiser

2016

European Journal of Mechanics - B/Fluids

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a b s t r a c tVortex breakdown of swirling, round jet flows is investigated in the compressible, subsonic regime by means of Direct Numerical Simulation (DNS). This is achieved by solving the compressible Navier-Stokes equations on a cylindrical grid using high-order spatial and temporal discretization schemes. TheReynolds number is Re = ρ The integral swirl number at the inflow is S int = 0.85. The parameters are chosen properly so as to make comparisons with existing experiments at lower Mach numbers possible while still enabling a study of compressible and baroclinic effects. Different from previous numerical investigations, a nozzle immersed in the fluid is included in the computational domain and is modelled as an isothermal no-slip wall, either rotating with the mean azimuthal flow direction or kept at rest. The present investigation aims to clarify the role played by the nozzle wall motion for the vortex breakdown of the swirling jet. We study the nozzle flow as well as the swirling jet flow simultaneously, a novelty for numerical investigations of vortex breakdown in swirling jets. Depending on the nozzle wall motion, the flow differs significantly upstream of the vortex breakdown: for the rotating nozzle, the flow inside the nozzle is purely laminar and the azimuthal boundary layer at the outer nozzle wall gives rise to the axisymmetric mode n = 0 and a single-helix type instability with azimuthal wave number n = 1. With the nozzle at rest, a transitional flow is observed within the nozzle where a helical instability with azimuthal wave number n = 12 dominates, growing in the boundary layer at the nozzle wall. For both nozzle setups, the helical instabilities observed for the nozzle flow interact with the developing vortex breakdown and the conical shear-layer downstream of the nozzle. For the nozzle at rest, this interaction results in a vortex breakdown configuration which is shifted in the upstream direction and which has a smaller radial and streamwise extent compared to the rotating nozzle case and the recirculation intensity is higher. The dominant frequency is highly influenced by the flow upstream of the vortex breakdown and is substantially higher for the nozzle at rest. Although the nozzle flow field differs for the two configurations and therefore alters the vortex breakdown downstream, a single-helix type instability n = 1 governing the vortex breakdown is found for both cases. This provides strong evidence for the robustness of the instability mechanisms leading to vortex breakdown.

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Section: Where Rmentioning

confidence: 99%

Section: Where Rmentioning

confidence: 99%