Development of Validation Approaches for Numerical Simulation of Combustion Instability using Flame Imaging

Abstract

Combustion dynamics are controlled by the coupling between heat addition and gas dynamic modes, hence their direct measurement and comparisons with prediction are key to improving computational tools as well as our fundamental understanding of the problem. Whereas gas dynamic modes are relatively easy to measure and compare, measurement and characterization of heat addition are much more difficult due to its complexity and the lack of any direct means of measurement. This paper demonstrates several methods for characterizing and comparing heat release from experiment and simulation. A model rocket combustor is used for the study. Comparisons are made for two configurations, one stable and one unstable. High-speed, line-of-sight imaging of OH* emission from the experiment was first phase averaged, and then treated with an Abel inversion routine to produce a dynamic, two-dimensional field of heat addition. The field before inversion could be compared to line-integrated calculations of heat release rate from three-dimensional large eddy simulations, and after inversion to azimuthally averaged cross-sections from simulations. Modal decomposition analysis of the two-dimensional fields were performed. The applicability and limitations of each comparison approach are assessed. Nomenclature J 0 = zero-order Bessel function of the first kind L op = length of oxidizer post, mm|inch p′ = dynamic pressure, MPa P cc = chamber pressure, MPa Φ = equivalence ratio ′ = unsteady term of a variable ω = frequency, Hz

Coupling between hydrodynamics, acoustics, and heat release in a self-excited unstable combustor

“…As a result, DMD results can prove to be a useful tool in experimental and simulation results' comparison. 68 Here, DMD is used to qualitatively compare the unsteady combustion responses in the experiment and simulations. In the case of the simulation data, the DMD is performed on the combustion heat release.…”

Modeling of a coaxial liquid oxygen/gaseous hydrogen injection element under high-frequency acoustic disturbances

“…Dynamic mode decomposition is described by Schmid [6] and is useful for identifying and sorting coherent §uctuations of data at di¨erent frequencies. Dynamic mode decomposition is often applied to study periodically §uctuating phenomena and has been previously used in combustion instability research in order to detect coherent §uctuations of §ame visualization data [7,8].…”

Self-Excited Non-Linear Acoustic Wave in a Single-Element Model Rocket Combustor and Its Influence on Flame

“…This assumption has been shown to hold well during periods of high amplitude oscillation where acoustic forcing causes axisymmetrical organization of the combustion field. 14) Assuming the emission images are a result of line-of-sight integration, neglecting absorption and diffraction, the transformed images give tomographic reconstruction of the radial distribution of light emission from the flame. Thus the images tell not only the axial but also the radial location of flame more clearly.…”