CFD-Based Investigation of Turbine Tonal Noise Induced by Steady Hot Streaks †

Abstract

Abstract:The interaction of steady hot streaks from an annular ring of combustion chambers with turbine rotating blades can potentially generate tonal noise. The relevance of this source mechanism in aeroengine noise is controversially discussed in the literature. In the present paper, the streak-turbine interaction is investigated using the computational fluid dynamics (CFD) method called harmonic balance (HB)-a truncated non-linear frequency domain approach with a high potential of reducing the computational effort. The investigated high-pressure turbine is composed of a single stator-rotor stage. The first part of the present paper compares the results obtained with the HB method to those obtained with the more established time-accurate unsteady Reynolds-averaged Navier-Stokes (URANS) approach and investigates their sensitivity with respect to the computational mesh density. Thereby, no streaks are simulated, and only the turbine alone tones are considered. Convincing results are obtained on aerodynamics and acoustics. The second part of the paper deals with a parametric study on the acoustical impact of steady hot streaks. The streaks are prescribed at the inlet of the stage using a boundary condition as an attempt to simulate a ring of combustor nozzles. No vorticity is coupled into the computational domain, as the objective is to measure the effect of temperature inhomogeneity only. Overall, the turbine appears to be slightly quieter with hot streaks. The streak-to-stator-vane ratio of 1-to-2 explains the generation of new acoustic modes with distinct azimuthal orders. The acoustic power amplitude of those additional modes scales roughly with the square of the temperature difference, the fourth-power of the diameter, and the square of the entropy difference. This last result agrees well with the 1D theory of Marble and Candel. The acoustic contribution of the unsteady force on the rotor blades due to the overspeed measured in the wakes of the streaks-resulting from the flow acceleration through the stator-remains an open question.

Entropy and Vorticity Wave Generation in Realistic Gas Turbine Combustors

“…The contradictory reported results, where entropy waves lead to an overall acoustic noise attenuation [16] or additional noise source [7,15,18], are inconclusive having considered only partially the nature of incoming entropy waves and the broadband noise at low frequencies. All investigations employed idealised entropy wave shapes, i.e.…”

“…Transient entropy waves being entrained into turbines are elongated by the acceleration forming streaks. Holewa et al [16] performed frequency domain simulations (based on the harmonic balance method), where such steady hot temperature streaks imposed at the inlet interact with the blade rows. The temperature inhomogeneity was found to decrease the acoustic noise compared to the homogeneous reference case.…”

The Challenge of Tonal Fan Noise Prediction for an Aircraft Engine in Flight

“…The main advantage is that this tends to be more efficient, especially when solutions are only needed at blade passing frequencies as is the case in the paper. In fact, both Frey et al [21] and Holewa et al [22] have shown that a HB simulation runs faster than a traditional uRANS simulation. Frey et al [21] simulated the tonal fan noise of DLR's Ultra High Bypass Ratio (UHBR) at the second blade passing frequency in approach conditions.…”

“…In addition to its computational efficiency, the authors were able to prove that the HB results match well with uRANS and experimental results. Holewa et al [22] used the approach to study the impact of the interaction of steady hot streaks with a high-pressure turbine stage on the overall tonal noise. They were able to show that the HB simulation, which was designed to resolve harmonics 1 and 2 of the BPF, ran 20 times faster than the uRANS simulation.…”

Fan tonal noise from aircraft aeroengines with short intake: A study at approach

“…struts and bifurcations). The formulation in the frequency domain called Harmonic Balance is an alternative method, attractive for two main reasons: (i) it enables a drastic reduction of the computational effort for the same level of accuracy 13 as uRANS, and (ii) it is much more powerful and robust in conjunction with the use of the phase shift boundary condition widely used in turbomachine simulations. 14,15 A detailed description of the Harmonic Balance method implemented in the DLR in-house CFD solver TRACE can be found elsewhere.…”