A 3D Navier-Stokes investigation of a high pressure turbine rotor blade including tip clearance effects is presented.
The 3D Navier-Stokes code developed at ONERA solves the three-dimensional unsteady set of mass-averaged Navier-Stokes equations by the finite volume technique. A one step Lax-Wendroff type scheme is used in a rotating frame of reference. An implicit residual smoothing technique has been implemented, which accelerates the convergence towards the steady state. A mixing length model adapted to 3D configurations is used.
The turbine rotor flow is calculated at transonic operating conditions. The tip clearance effect is taken into account. The gap region is discretized using more than 55,000 points within a multi-domain approach.
The solution accounts for the relative motion of the blade and casing surfaces. The total mesh is composed of five sub-domains and counts 710,000 discretization points. The effect of the tip clearance on the main flow is demonstrated. The calculation results are compared to a 3D inviscid calculation, without tip clearance.
This paper presents an overview of numerical simulations performed at ONERA on turbomachinery configurations which include technological effects, such as tip clearance, hub disk leakage, circumferential and noncircumferential casing treatments (CTs), blade fillets, and cooling holes. An overset grid approach (Chimera technique) is used to simulate these geometrical effects with ONERA's structured computational fluid dynamics (CFD) solver elsA. Calculations performed on the different configurations enable to quantify the impact of these technological effects on the flow solution.
The Proper Orthogonal Decomposition method is applied to the instantaneous velocity field within the rotor-stator inter-row region of a high-speed high-pressure centrifugal compressor. The processed data come from experiments and numerical simulations. In comparison with a Fourier transform, the POD gives the best modal approximation for both initial fields, in terms of the energy expressed on any given number of modes to be taken into account: to reach 98% of the total energy of the velocity field, the required number of POD modes is up to nine times lower than the number of Fourier harmonics. The individual POD modes are given and show that the unsteady rotor-stator interaction is already present in the very first modes.
The goal of this study was to realize predictions of tonal noise generated by a SNECMA turbofan mock up with a heterogeneous stator and radiated from the inlet using as input a modal decomposition made in the inlet duct wall. A numerical approach based on the CAA (Computational AeroAcoustics) code sAbrinA.V0 with an equivalent source term recently implemented is used as well as an analytical methodology using a Wiener-Hopf technique and an uniform flow assumption. Even if directivities from raw experimental data exhibit significant variations of noise level in the azimuthal direction proving that correlation effect between modes seems to be not negligible for tonal noise, the hypothesis of incoherent modes inducing axisymmetric directivities allow to compare reasonably well with measured data averaged azimuthally. Comparisons between theoretical and numerical predictions confirm the practical interest of using simplified analytical methods even if clear improvement are provided by more complex and time consuming methods like CAA. Especially, for polar angles between 20 • and 70 • , a very good agreement is obtained with a maximum discrepancy of 0.7 dB on overall sound pressure level for the three first tones.
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