Fluid-Structure Interaction of Flexible Whisker-Type Beams and Its Implication for Flow Sensing by Pair-Wise Correlation

(1) Background: Sensing of critical events or flow signatures in nature often presents itself as a coupled interaction between a fluid and arrays of slender flexible beams, such a wind-hairs or whiskers. It is hypothesized that important information is gained in highly noisy environments by the inter-correlation within the array. (2) Methods: The present study uses a model sea lion head with artificial whiskers in the form of slender beams (optical fibres), which are subjected to a mean flow with overlaid turbulent structures generated in the wake of a cylinder. Motion tracking of the array of fibres is used to analyse the correlation of the bending deformations of pairs of fibres. (3) Results: Cross-correlation of the bending signal from tandem pairs of whiskers proves that the detection of vortices and their passage along the animals head is possible even in noisy environments. The underlying pattern, during passage of a vortex core, is a jerk-like response of the whiskers, which can be found at later arrival-times in similar form in the downstream whisker's response. (4) Conclusion: Coherent vortical structures can be detected from cross-correlation of pairs of cantilever-beam like sensors even in highly turbulent flows. Such vortices carry important information within the environment, e.g. the underlying convection velocity. More importantly in nature, these vortices are characteristic elementary signals left by prey and predators. The present work can help to further develop flow, or critical event, sensory systems which can overcome high noise levels due to the proposed correlation principle.

Download Full-text

Fluid-Structure Interaction of Flexible Whisker-Type Beams and Its Implications for Flow Sensing by Pair-Wise Correlation

Fluids ◽

10.3390/fluids6030102 ◽

2021 ◽

Vol 6 (3) ◽

pp. 102

Author(s):

Raphael Glick ◽

Muthukumar Muthuramalingam ◽

Christoph Brücker

Keyword(s):

Turbulent Flows ◽

Motion Tracking ◽

Cross Correlation ◽

Critical Event ◽

Noisy Environments ◽

Mean Flow ◽

Turbulent Structures ◽

Flexible Beams ◽

Arrival Times ◽

Slender Beams

(1) Background: Sensing of critical events or flow signatures in nature often presents itself as a coupled interaction between a fluid and arrays of slender flexible beams, such a wind-hairs or whiskers. It is hypothesized that important information is gained in highly noisy environments by the inter-correlation within the array. (2) Methods: The present study uses a model sea lion head with artificial whiskers in the form of slender beams (optical fibres), which are subjected to a mean flow with overlaid turbulent structures generated in the wake of a cylinder. Motion tracking of the array of fibres is used to analyse the correlation of the bending deformations of pairs of fibres. (3) Results: Cross-correlation of the bending signal from tandem pairs of whiskers proves that the detection of vortices and their passage along the animals head is possible even in noisy environments. The underlying pattern, during passage of a vortex core, is a jerk-like response of the whiskers, which can be found at later arrival-times in similar form in the downstream whisker’s response. (4) Conclusions: Coherent vortical structures can be detected from cross-correlation of pairs of cantilever-beam like sensors even in highly turbulent flows. Such vortices carry important information within the environment, e.g., the underlying convection velocity. More importantly in nature, these vortices are characteristic elementary signals left by prey and predators. The present work can help to further develop flow, or critical event, sensory systems which can overcome high noise levels due to the proposed correlation principle.

Download Full-text

Voltage rise anemometry in turbulent flows applied to internal combustion engines

Experiments in Fluids ◽

10.1007/s00348-021-03226-3 ◽

2021 ◽

Vol 62 (6) ◽

Author(s):

Michael Wörner ◽

Gregor Rottenkolber

Keyword(s):

Turbulent Flows ◽

Internal Combustion Engines ◽

Clear Correlation ◽

Combustion Engines ◽

Mean Flow ◽

Voltage Rise ◽

Mathematical Correlation ◽

Thermodynamic Conditions ◽

Secondary Voltage ◽

Cylinder Flow

AbstractIn an experimental procedure, a voltage rise anemometry is developed as a measurement technique for turbulent flows. Initially, fundamental investigations on a specific wind tunnel were performed for basic understanding and calibration purpose. Thus, a mathematical correlation is derived for calculating flow from measured secondary voltage of an ignition system under different thermodynamic conditions. Subsequently, the derived method was applied on a spark-ignited engine to measure in-cylinder flow. Therefore, no changes on combustion chamber were necessary avoiding any interferences of the examined flow field. Comparing four different engine configurations, a study of mean flow and turbulence was performed. Moreover, the results show a clear correlation between measured turbulence and analysed combustion parameters. Graphic abstract

Download Full-text

Characterization of Geometrical and Temporal Properties of Large-scale Motions in Turbulent Flows

10.5194/egusphere-egu21-14221 ◽

2021 ◽

Author(s):

Christina Tsai ◽

Kuang-Ting Wu

Keyword(s):

Turbulent Flow ◽

Turbulent Flows ◽

Coherent Structures ◽

Large Scale ◽

Streamwise Velocity ◽

Turbulent Structures ◽

Temporal Properties ◽

Turbulent Statistics ◽

Spatial Locations

<p>It is demonstrated that turbulent boundary layers are populated by a hierarchy of recurrent structures, normally referred to as the coherent structures. Thus, it is desirable to gain a better understanding of the spatial-temporal characteristics of coherent structures and their impact on fluid particles. Furthermore, the ejection and sweep events play an important role in turbulent statistics. Therefore, this study focuses on the characterizations of flow particles under the influence of the above-mentioned two structures.</p><div><span>With regard to the geometry of turbulent structures, </span><span>Meinhart & Adrian (1995)&#160;</span>first highlighted the existence of large and irregularly shaped regions of uniform streamwise momentum zone (hereafter referred to as a uniform momentum zone, or UMZs), regions of relatively similar streamwise velocity with coherence in the streamwise and wall-normal directions. &#160;<span>Subsequently,&#160;</span><span>de Silva et al. (2017)&#160;</span><span>provided a detection criterion that had previously been utilized to locate the uniform momentum zones (UMZ) and demonstrated the application of this criterion to estimate the spatial locations of the edges that demarcates UMZs.</span></div><div>&#160;</div><div>In this study, detection of the existence of UMZs is a pre-process of identifying the coherent structures. After the edges of UMZs are determined, the identification procedure of ejection and sweep events from turbulent flow DNS data should be defined. As such, an integrated criterion of distinguishing ejection and sweep events is proposed. Based on the integrated criterion, the statistical characterizations of coherent structures from available turbulent flow data such as event durations, event maximum heights, and wall-normal and streamwise lengths can be presented.</div>

Download Full-text

Measurements and Characterization of Turbulence in the Tip Region of an Axial Compressor Rotor

Journal of Turbomachinery ◽

10.1115/1.4037773 ◽

2017 ◽

Vol 139 (12) ◽

Cited By ~ 4

Author(s):

Yuanchao Li ◽

Huang Chen ◽

Joseph Katz

Keyword(s):

Strain Rate ◽

Shear Layer ◽

Turbulent Flows ◽

Reynolds Stress ◽

Suction Side ◽

Stress And Strain ◽

Spatial And Temporal Variability ◽

Mean Flow ◽

The Mean ◽

Stress And Strain Rate

Modeling of turbulent flows in axial turbomachines is challenging due to the high spatial and temporal variability in the distribution of the strain rate components, especially in the tip region of rotor blades. High-resolution stereo-particle image velocimetry (SPIV) measurements performed in a refractive index-matched facility in a series of closely spaced planes provide a comprehensive database for determining all the terms in the Reynolds stress and strain rate tensors. Results are also used for calculating the turbulent kinetic energy (TKE) production rate and transport terms by mean flow and turbulence. They elucidate some but not all of the observed phenomena, such as the high anisotropy, high turbulence levels in the vicinity of the tip leakage vortex (TLV) center, and in the shear layer connecting it to the blade suction side (SS) tip corner. The applicability of popular Reynolds stress models based on eddy viscosity is also evaluated by calculating it from the ratio between stress and strain rate components. Results vary substantially, depending on which components are involved, ranging from very large positive to negative values. In some areas, e.g., in the tip gap and around the TLV, the local stresses and strain rates do not appear to be correlated at all. In terms of effect on the mean flow, for most of the tip region, the mean advection terms are much higher than the Reynolds stress spatial gradients, i.e., the flow dynamics is dominated by pressure-driven transport. However, they are of similar magnitude in the shear layer, where modeling would be particularly challenging.

Download Full-text

Markovian inhomogeneous closures for Rossby waves and turbulence over topography

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.784 ◽

2018 ◽

Vol 858 ◽

pp. 45-70

Author(s):

Jorgen S. Frederiksen ◽

Terence J. O’Kane

Keyword(s):

Turbulent Flows ◽

Rossby Waves ◽

Time History ◽

Direct Interaction ◽

Mean Flow ◽

Current Time ◽

Fluctuation Dissipation ◽

Large Ensembles ◽

Direct Interaction Approximation ◽

The Impact

Manifestly Markovian closures for the interaction of two-dimensional inhomogeneous turbulent flows with Rossby waves and topography are formulated and compared with large ensembles of direct numerical simulations (DNS) on a generalized $\unicode[STIX]{x1D6FD}$-plane. Three versions of the Markovian inhomogeneous closure (MIC) are established from the quasi-diagonal direct interaction approximation (QDIA) theory by modifying the response function to a Markovian form and employing respectively the current-time (quasi-stationary) fluctuation dissipation theorem (FDT), the prior-time (non-stationary) FDT and the correlation FDT. Markov equations for the triad relaxation functions are derived that carry similar information to the time-history integrals of the non-Markovian QDIA closure but become relatively more efficient for long integrations. Far from equilibrium processes are studied, where the impact of a westerly mean flow on a conical mountain generates large-amplitude Rossby waves in a turbulent environment, over a period of 10 days. Excellent agreement between the evolved mean streamfunction and mean and transient kinetic energy spectra are found for the three versions of the MIC and two variants of the non-Markovian QDIA compared with an ensemble of 1800 DNS. In all cases mean Rossby wavetrain pattern correlations between the closures and the DNS ensemble are greater than 0.9998.

Download Full-text

Improved Prediction of Turbomachinery Flows Using Near-Wall Reynolds-Stress Model

Journal of Turbomachinery ◽

10.1115/1.1426083 ◽

2001 ◽

Vol 124 (1) ◽

pp. 86-99 ◽

Cited By ~ 38

Author(s):

G. A. Gerolymos ◽

J. Neubauer ◽

V. C. Sharma ◽

I. Vallet

Keyword(s):

Experimental Data ◽

Turbulent Flows ◽

Reynolds Stress ◽

Turbulence Models ◽

Reynolds Stress Model ◽

Stress Model ◽

Reynolds Stresses ◽

Mean Flow ◽

Flow Equations ◽

Near Wall

In this paper an assessment of the improvement in the prediction of complex turbomachinery flows using a new near-wall Reynolds-stress model is attempted. The turbulence closure used is a near-wall low-turbulence-Reynolds-number Reynolds-stress model, that is independent of the distance-from-the-wall and of the normal-to-the-wall direction. The model takes into account the Coriolis redistribution effect on the Reynolds-stresses. The five mean flow equations and the seven turbulence model equations are solved using an implicit coupled OΔx3 upwind-biased solver. Results are compared with experimental data for three turbomachinery configurations: the NTUA high subsonic annular cascade, the NASA_37 rotor, and the RWTH 1 1/2 stage turbine. A detailed analysis of the flowfield is given. It is seen that the new model that takes into account the Reynolds-stress anisotropy substantially improves the agreement with experimental data, particularily for flows with large separation, while being only 30 percent more expensive than the k−ε model (thanks to an efficient implicit implementation). It is believed that further work on advanced turbulence models will substantially enhance the predictive capability of complex turbulent flows in turbomachinery.

Download Full-text

The Development of Swirling Decaying Laminar Flow in an Annular Pipe

E3S Web of Conferences ◽

10.1051/e3sconf/20185103001 ◽

2018 ◽

Vol 51 ◽

pp. 03001

Author(s):

Baiman Chen ◽

Frank G.F. Qin ◽

Youyuan Shao ◽

Hanmin Xiao ◽

Simin Huang ◽

...

Keyword(s):

Turbulent Flows ◽

Pipe Flow ◽

Tangential Component ◽

Duct Flow ◽

Mean Flow ◽

Entry Length ◽

Swirl Angle ◽

Practical Engineering ◽

Inlet Swirl ◽

Annular Pipe

Work on the hydrodynamic entry length of pipe and duct flow has been well studied over the years. The assumption of fully developed flows is commonly used in many practical engineering applications (e.g. Moody's chart). For laminar axial pipe flow, the hydrodynamic entry length can be found through the monomial proposed by Kays, Shah and Bhatti (KSB) (Lh=0.056ReDh). In contrast, several approximations exist for fully turbulent flows (i.e. 10Dh-150Dh). Through theoretical and numerical investigations, the hydrodynamic entry length for swirling decaying pipe flow in the laminar regime is investigated. It was found that, the development length Lh for the axial velocity profile changes when a tangential component is added to the mean flow. The reduction in the hydrodynamic length was found to be dependent on the inlet swirl angle θ. The results indicate that a modification can be made on the KSB equation for two-dimensional swirling annular pipe flow.

Download Full-text

Drag Reduction in Synthetic Seawater by Flexible and Rigid Polymer Addition Into a Rotating Cylindrical Double Gap Device

Journal of Fluids Engineering ◽

10.1115/1.4031229 ◽

2015 ◽

Vol 138 (2) ◽

Cited By ~ 17

Author(s):

Rafhael M. Andrade ◽

Anselmo S. Pereira ◽

Edson J. Soares

Keyword(s):

Drag Reduction ◽

Turbulent Flows ◽

Salt Concentration ◽

Polymer Concentration ◽

Transient Behavior ◽

Turbulent Structures ◽

Polymer Addition ◽

Rigid Polymer ◽

Potential Applications ◽

Poly Ethylene

Flexible and rigid long chain polymers in very dilute solutions can significantly reduce the drag in turbulent flows. The polymers successively stretch and coil by interacting with the turbulent structures, which changes the turbulent flow and further imposes a transient behavior on the drag reduction (DR) as well as a subsequent mechanical polymer degradation. This time-dependent phenomenon is strongly affected by a number of parameters, which are analyzed here, such as the Reynolds number, polymer concentration, polymer molecular weight, and salt concentration. This last parameter can dramatically modify the polymeric structure. The investigation of the salt concentration's impact on the DR is mostly motivated by some potential applications of this technique to ocean transport and saline fluid flows. In the present paper, a cylindrical double gap rheometer device is used to study the effects of salt concentration on DR over time. The reduction of drag is induced by three polymers: poly (ethylene oxide) (PEO), polyacrylamide (PAM), and xanthan gum (XG). These polymers are dissolved in deionized water both in the presence of salt and in its absence. The DR is displayed from the very start of the test to the time when the DR achieves its final level of efficiency, following the mechanical degradations. The presence of salt in PEO and XG solutions reduces the maximum DR, DRmax, as well as the time to achieve it. In contrast, the DR does not significantly change over the time for PAM solutions upon the addition of salt.

Download Full-text

An Acoustic Time-of-Flight Approach for Unsteady Temperature Measurements: Characterization of Entropy Waves in a Model Gas Turbine Combustor

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4034542 ◽

2016 ◽

Vol 139 (4) ◽

Cited By ~ 8

Author(s):

Dominik Wassmer ◽

Bruno Schuermans ◽

Christian Oliver Paschereit ◽

Jonas P. Moeck

Keyword(s):

Gas Turbine ◽

Acoustic Waves ◽

Fuel Injection ◽

Acoustic Pulse ◽

Time Of Flight ◽

Phase Lag ◽

Mean Flow ◽

Unsteady Temperature ◽

Arrival Times ◽

Flow Velocities

Lean premixed combustion promotes the occurrence of thermoacoustic phenomena in gas turbine combustors. One mechanism that contributes to the flame–acoustic interaction is entropy noise. Fluctuations of the equivalence ratio in the mixing section cause the generation of hot spots in the flame. These so-called entropy waves are convectively transported to the first stage of the turbine and generate acoustic waves that travel back to the flame; a thermoacoustic loop is closed. However, due to the lack of experimental tools, a detailed investigation of entropy waves in gas turbine combustion systems has not been possible up to now. This work presents an acoustic time-of-flight based temperature measurement method which allows the measurement of temperature fluctuations in the relevant frequency range. A narrow acoustic pulse is generated with an electric spark discharge close to the combustor wall. The acoustic response is measured at the same axial location with an array of microphones circumferentially distributed around the combustion chamber. The delay in the pulse arrival times corresponds to the line-integrated inverse speed of sound. For the measurement of entropy waves in an atmospheric combustion test rig, fuel is periodically injected into the mixing tube of a premixed combustor. The subsequently generated entropy waves are measured for different forcing frequencies of the fuel injection and for different mean flow velocities in the combustor. The amplitude decay and phase lag of the entropy waves adhere well to a Strouhal number scaling for different mean flow velocities.

Download Full-text

Large-Eddy Simulations of Wall Bounded Turbulent Flows Using Unstructured Linear Reconstruction Techniques

Journal of Turbomachinery ◽

10.1115/1.4028549 ◽

2015 ◽

Vol 137 (5) ◽

Cited By ~ 7

Author(s):

Dario Amirante ◽

Nicholas J. Hills

Keyword(s):

Reynolds Number ◽

Turbulent Flows ◽

Outer Radius ◽

Large Eddy Simulations ◽

Test Cases ◽

Mean Flow ◽

Flow Equations ◽

Turbulent Statistics ◽

Large Eddy ◽

Least Squares Approach

Large-eddy simulations (LES) of wall bounded, low Mach number turbulent flows are conducted using an unstructured finite-volume solver of the compressible flow equations. The numerical method employs linear reconstructions of the primitive variables based on the least-squares approach of Barth. The standard Smagorinsky model is adopted as the subgrid term. The artificial viscosity inherent to the spatial discretization is maintained as low as possible reducing the dissipative contribution embedded in the approximate Riemann solver to the minimum necessary. Comparisons are also discussed with the results obtained using the implicit LES (ILES) procedure. Two canonical test-cases are described: a fully developed pipe flow at a bulk Reynolds number Reb = 44 × 103 based on the pipe diameter, and a confined rotor–stator flow at the rotational Reynolds number ReΩ = 4 × 105 based on the outer radius. In both cases, the mean flow and the turbulent statistics agree well with existing direct numerical simulations (DNS) or experimental data.

Download Full-text