POD Mode Robustness for the Turbulent Jet Sampled with PIV
A POD robustness analysis was conducted on data obtained from two independent experiments on the turbulent axisymmetric jet. Two-component (2D2C) particle image velocimetry (PIV) measurements were conducted in a streamwise plane cutting through the center
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POD Mode Robustness for the Turbulent Jet Sampled with PIV A. Hodži´c, K.E. Meyer, and C.M. Velte
10.1 POD and Big Data An important challenge in the description and simulation of turbulence is the large amount of information that is needed to describe even relatively simple flows in detail. The frequent disagreement between Reynolds averaged Navier– Stokes-based simulations and experiments is well known. Albeit, direct numerical simulations and in certain cases large eddy simulations tend to agree fairly well with experiments, their practical implementation introduces the problem of data storage. The experimentalist, however, experiences the same problem, using high speed particle image velocimetry (PIV) systems and even high speed volumetric PIV systems providing fully three dimensional velocity fields. Another challenge is how do we verify simulations against experiments and ensure that we indeed have simulated the same flow that we have measured? POD is a useful tool allowing us to extract statistical data related to dynamic flow structures and can thereby not only be used to gain understanding of the dynamics of the flow, but can also be used as a tool to validate the dynamical aspect of simulations to experiments. Finally, the POD can be used to filter down large batches of data to encapsulate only the most essential information of the flow and thereby compressing the data amount to a mere fraction of its original size.
A. Hodži´c () • K.E. Meyer • C.M. Velte Department of Mechanical Engineering, Technical University of Denmark, Building 403, 2800 Kgs. Lyngby, Denmark e-mail: [email protected]; [email protected]; [email protected] © Springer International Publishing Switzerland 2017 A. Pollard et al. (eds.), Whither Turbulence and Big Data in the 21st Century?, DOI 10.1007/978-3-319-41217-7_10
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10.2 Introduction The turbulent free axisymmetric jet constitutes a unique opportunity for the study of turbulence due to its homogeneous streamwise direction recovered from the logarithmic mapping of the velocity field [4, 26]. The technical and practical aspects and limitations of the study of Wänström [26], not least regarding domain size coverage and spatial resolution of the PIV measurements, have left open the question of the robustness of the results with respect to the domain. With the equipment at hand, [26] managed only to cover the jet to within a similarity radius of approximately D 2:0 for the streamwise and crossplane. Similar attempts to test the robustness of the POD analysis using extensive (138) hot-wire rakes can be found in [7] and also in the work of [18]. Going beyond this limit naturally requires evaluation for confidence in the robustness of the results, not least since the POD analysis assumes a domain of finite energy for the analysis to hold [8]. The POD was applied in the crossplane of the turbulent jet by Glauser et al. [12] using an array of hot-wire probes, and later by Holmes et al. [16], Citriniti and George [2], Gamard et al. [6], Jung et al. [19] and Gamard e
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