1,720,986 research outputs found
Dataset for "An experimental investigation of a high Reynolds number turbulent wake generated by a vehicle-like bluff body"
No full textFiles containing the coordinates and 3-component mean velocity fields.
Paper DOI: https://doi.org/10.1103/5m65-46ng</span
Experimental investigation of a high Reynolds number turbulent wake generated by a vehicle-like bluff body
No full textThis study uses stereo-particle image velocimetry to describe the wake behind a multi-wake model at a Reynolds number of 5.64×105 based on the model lengt
Role of parasitic modes in nonlinear closure via the resolvent feedback loop
Full text linkWe use the feedback formulation of McKeon and Sharma [J. Fluid Mech. 658, 336 (2010)], where the nonlinear term in the Navier-Stokes equations is treated as an intrinsic forcing of the linear resolvent operator, to educe the structure of fluctuations in the range of scales (wave numbers) where linear mechanisms are not active. In this region, the absence of dominant linear mechanisms is reflected in the lack of low-rank characteristics of the resolvent and in the disagreement between the structure of resolvent modes and actual flow features. To demonstrate the procedure, we choose low Reynolds number cylinder flow and the Couette equilibrium solution EQ1, which are representative of very low-rank flows dominated by one linear mechanism. The former is evolving in time, allowing us to compare resolvent modes with dynamic mode decomposition (DMD) modes at the first and second harmonics of the shedding frequency. There is a match between the modes at the first harmonic but not at the second harmonic where there is no separation of the resolvent operator's singular values. We compute the self-interaction of the resolvent mode at the shedding frequency and illustrate its similarity to the nonlinear forcing of the second harmonic. When it is run through the resolvent operator, the “forced” resolvent mode shows better agreement with the DMD mode. A similar phenomenon is observed for the fundamental streamwise wave number of the EQ1 solution and its second harmonic. The importance of parasitic modes, labeled as such since they are driven by the amplified frequencies, is their contribution to the nonlinear forcing of the main amplification mechanisms as shown for the shedding mode, which has subtle discrepancies with its DMD counterpart
Rigid and flexible wings subject to large intensity turbulence
No full textA rigid and flexible wing with NACA0012 profile was subjected to clean and turbulent conditions. The deformation of the flexible wing was studied in the clean flow condition using digital image correlation. Turbulent conditions generated by an active grid included turbulence intensities and integral length scales spanning from Tu = 9.5 % to 19.6 % and Lx = 0.14 m to 0.33 m respectively. A 6-axis load cell was used to measure the forces and moments generated by both wings in all flow conditions. The onset of stall was delayed with the introduction of free stream turbulence and similarly the peak time averaged lift coefficient increased, however at large intensities this improvement began to diminish. A comparison between the turbulent length scale and excitation of particular structural modes in the flexible wing were observed, sharing similarities with previous studies involving flexible wings in harmonic gusts.</p
Energy transfer in turbulent channel flows and implications for resolvent modelling
No full textWe analyse the inter-scale transfer of energy for two types of plane Poiseuille flow: the P4U exact coherent state of Park & Graham (J. Fluid Mech., vol. 782, 2015, pp. 430-454) and turbulent flow in a minimal channel. For both flows, the dominant energy-producing modes are streamwise-constant streaks with a spanwise spacing of approximately 100 wall units. Since the viscous dissipation for these scales is not sufficient to balance production, the nonlinear terms redistribute the excess energy to other scales. Spanwise-constant scales (that is, Tollmien-Schlichting-like modes with zero spanwise wavenumber), in particular, account for a significant amount of net energy gain from the nonlinear terms. We compare the energy balance to predictions from resolvent analysis, and we show that it does not model energy transfer well. Nevertheless, we find that the energy transferred from the streamwise-constant streaks can be predicted reasonably well by a Cess eddy viscosity profile. As such, eddy viscosity is an effective model for the nonlinear terms in resolvent analysis and explains good predictions for the most energetic streamwise-constant streaks. It also improves resolvent modes as a basis for structures whose streamwise lengths are greater than their spanwise widths by counteracting non-normality of the resolvent operator. This is quantified by computing the inner product between the optimal resolvent forcing and response modes, which is a metric of non-normality. Eddy viscosity does not respect the conservative nature of the nonlinear energy transfer, which must sum to zero over all scales. Since eddy viscosity tends to remove energy, it is less effective in modelling nonlinear transport for scales that receive energy from the nonlinear terms.</p
Dataset supporting the publication "Three-dimensional variational data assimilation of separated flows using time-averaged experimental data"
No full textDataset supporting the publication "Three-dimensional variational data assimilation of separated flows using time-averaged experimental data" by U. Cadambi Padmanaban, B. Ganapathisubramani and S. Symon, in PRF journal, DOI: 10.1103/q7sd-q3dn
This dataset includes the data for the above manuscript. The data is presented in a zipped file: PRF_UCP_data.zip
Data is presented in .csv format named after the figures that were developed from this data.
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Three-dimensional variational data assimilation of separated flows using time-averaged experimental data
No full textWe present a novel framework for assimilating planar PIV experimental data using a variational approach to enhance the predictions of the Spalart–Allmaras RANS turbulence model. Our method applies three-dimensional constraints to the assimilation of mean velocity data, incorporating a corrective forcing term in the momentum equations. The advantages of this approach are highlighted through a direct comparison with traditional two-dimensional assimilation using the same experimental dataset. We demonstrate its efficacy by assimilating the deep stall flow over a NACA0012 airfoil at a angle of attack and a chord-based Reynolds number of . We find that in two-dimensional assimilation, the corrective forcing term compensates not only for physical modeling errors but also for the lack of divergence in the experimental data. This conflation makes it difficult to isolate the effects of measurement inconsistencies from deficiencies in the turbulence model. In contrast, three-dimensional assimilation allows the corrective forcing term to primarily address experimental setup errors while enabling the turbulence model to more accurately capture the flow physics. We establish the benefits of three-dimensional assimilation through its ability to account for the inherent three-dimensionality of the flow, thereby enabling more physically consistent reconstructions of key quantities such as pressure, lift force, and eddy viscosity
Comparing reduced order model forms for nonlinear dynamical systems
No full textThe time domain solution of a chaotic system governed by a set of nonlinear equations is computationally expensive and ill suited for parametric searches. This work investigates the use of reduced order models to distill, both from data and equations, an equivalent but more advantageous mathematical representation. Two types of reduced order model are presented, data-driven, non-intrusive approaches and a model-derived, intrusive alternative. Three test cases are used for assessing the predictive capability of the models: a) Lorenz 1963 model; b) Moehlis model; and c) Lorenz 1996 model. Various key performance indices are selected to quantify the accuracy of the reduced order models, including over the short and long time scales. The small size of the test cases, up to 220 states for Lorenz 1996 model, prevented us from executing a projection of the reduced order models onto a smaller basis. Hence, the focus was on recovering the underlying governing equations and on the reconstruction of the physical features. For each reduced order model, details concerning the practical implementation and the model generation are also given.</p
Aeroelastic wing performance in high intensity turbulence: integral length scale effects
No full textThe impact of variations in the integral length scale of incoming free-stream turbulence onan aeroelastic NACA0012 wing is investigated using force, moment and PIV measurements. Ata chord-based Reynolds number
Dataset for "Effects of fetch length on turbulent boundary layer recovery past a step-change in surface roughness"
No full textData used to plot all figures in the respective article, the dataset contains
supplementary materials.xlsx in the form of 11 spreadsheets
Paper DOI: https://doi.org/10.1017/jfm.2025.311
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