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Publications (10 of 196) Show all publications
Lupi, V., Örlü, R. & Schlatter, P. (2024). Direct Numerical Simulations of Turbulent Flow in Helical Pipes. In: ERCOFTAC Series: (pp. 362-367). Springer Science and Business Media B.V., 31
Open this publication in new window or tab >>Direct Numerical Simulations of Turbulent Flow in Helical Pipes
2024 (English)In: ERCOFTAC Series, Springer Science and Business Media B.V. , 2024, Vol. 31, p. 362-367Chapter in book (Other academic)
Abstract [en]

Direct numerical simulations of the fully developed turbulent flow through helical pipes are performed. The numerical procedure is described, and a validation of the volume force driving the flow is presented. A comparison of the turbulence statistics against literature data is also reported.

Place, publisher, year, edition, pages
Springer Science and Business Media B.V., 2024
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-340778 (URN)10.1007/978-3-031-47028-8_55 (DOI)2-s2.0-85178107205 (Scopus ID)
Note

QC 20231214

Available from: 2023-12-14 Created: 2023-12-14 Last updated: 2023-12-14Bibliographically approved
Dróżdż, A., Örlü, R., Sokolenko, V., Schlatter, P., Elsner, W. & Niegodajew, P. (2024). Hot-wire spatial resolution issues in adverse pressure gradient turbulent boundary layers. Measurement, 237, Article ID 115229.
Open this publication in new window or tab >>Hot-wire spatial resolution issues in adverse pressure gradient turbulent boundary layers
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2024 (English)In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 237, article id 115229Article in journal (Refereed) Published
Abstract [en]

The effect of a finite length of hot-wire probe sensor length on the measured streamwise velocity fluctuations is well understood in canonical wall-bounded flow, where the small-scale energy has been found to be universal and invariant with Reynolds number. A straightforward application of that assumption to non-canonical flows such as strong adverse pressure gradient (APG) flows has, however, been hampered since the effect of Re and APG could not conclusively be studied separately due to the lack of data with a clear scale separation. The present experimental investigation at Reτ≈4000 in weak, moderate and strong APGs with different wire length shows that spatial averaging effects are not only limited to the inner layer. A note of caution is hence warranted for measurements that seemingly try to take the bias effect of spatial attenuation into account by performing measurements with albeit long but fixed viscous-scaled wire length.

Place, publisher, year, edition, pages
Elsevier BV, 2024
Keywords
Adverse pressure gradient, Hot-wire anemometry, Turbulent boundary layer, Velocity fluctuations measurement
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-350676 (URN)10.1016/j.measurement.2024.115229 (DOI)2-s2.0-85198035032 (Scopus ID)
Note

QC 20240719

Available from: 2024-07-17 Created: 2024-07-17 Last updated: 2024-07-19Bibliographically approved
Mallor, F., Liu, J., Peplinski, A., Vinuesa, R., Örlü, R., Weinkauf, T. & Schlatter, P. (2024). In-Situ Analysis of Backflow Events and Their Relation to Separation in Wings Through Well-Resolved LES. In: ERCOFTAC Series: (pp. 17-22). Springer Science and Business Media B.V., 31
Open this publication in new window or tab >>In-Situ Analysis of Backflow Events and Their Relation to Separation in Wings Through Well-Resolved LES
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2024 (English)In: ERCOFTAC Series, Springer Science and Business Media B.V. , 2024, Vol. 31, p. 17-22Chapter in book (Other academic)
Abstract [en]

Wall-bounded turbulent flows as those occurring in transportation (e.g. aviation) or industrial applications (e.g turbomachinery), are usually subjected to pressure gradients (PGs). The presence of such PGs affects greatly the development and physics of the turbulent boundary layer (TBL), making it an open research area. An important phenomena associated with the presence of strong adverse PGs (APGs) as appearing in wings, is the separation of the boundary layer, which can lead to stall.

Place, publisher, year, edition, pages
Springer Science and Business Media B.V., 2024
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-340780 (URN)10.1007/978-3-031-47028-8_3 (DOI)2-s2.0-85178156992 (Scopus ID)
Note

QC 20231214

Available from: 2023-12-14 Created: 2023-12-14 Last updated: 2023-12-14Bibliographically approved
Pasch, S., Leister, R., Gatti, D., Örlü, R., Frohnapfel, B. & Kriegseis, J. (2024). Measurements in a Turbulent Channel Flow by Means of an LDV Profile Sensor. Flow Turbulence and Combustion, 113(1), 195-213
Open this publication in new window or tab >>Measurements in a Turbulent Channel Flow by Means of an LDV Profile Sensor
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2024 (English)In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 113, no 1, p. 195-213Article in journal (Refereed) Published
Abstract [en]

Spatially and temporally resolved velocity measurements in wall-bounded turbulent flows remain a challenge. Contrary to classical laser Doppler velocimetry (LDV) measurements, the laser Doppler velocity profile sensor (LDV-PS) allows the combined measurement of tracer particle position and velocity, which makes it a promising tool. To assess its feasibility a commercial LDV-PS is employed in a turbulent channel flow at Reτ= 350 . Additionally, the measurement and signal-processing accuracies of velocity and location are evaluated for various tracer-object sizes and velocities. On this basis, the turbulent channel flow measurements are evaluated and compared to reference data from direct numerical simulations. Thus, potentials of the LDV-PS are investigated for different regions of the flow and various data processing routines as well as the experimental practice are discussed from an application perspective.

Place, publisher, year, edition, pages
Springer Nature, 2024
Keywords
LDV profile sensor, Near-wall measurements, Turbulent channel flow
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-350320 (URN)10.1007/s10494-023-00469-4 (DOI)001063147700001 ()2-s2.0-85170404471 (Scopus ID)
Note

QC 20240711

Available from: 2024-07-11 Created: 2024-07-11 Last updated: 2024-07-11Bibliographically approved
Lupi, V., Canton, J., Rinaldi, E., Örlü, R. & Schlatter, P. (2024). Modal stability analysis of toroidal pipe flow approaching zero curvature. Journal of Fluid Mechanics, 987, Article ID A40.
Open this publication in new window or tab >>Modal stability analysis of toroidal pipe flow approaching zero curvature
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2024 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 987, article id A40Article in journal (Refereed) Published
Abstract [en]

The present study investigates the modal stability of the steady incompressible flow inside a toroidal pipe for values of the curvature (ratio between pipe and torus radii) approaching zero, i.e. the limit of a straight pipe. The global neutral stability curve for is traced using a continuation algorithm. Two different families of unstable eigenmodes are identified. For curvatures below, the critical Reynolds number is proportional to. Hence, the critical Dean number is constant,. This behaviour confirms that the Hagen-Poiseuille flow is stable to infinitesimal perturbations for any Reynolds number and suggests that a continuous transition from the curved to the straight pipe takes place as far as it regards the stability properties. For low values of the curvature, an approximate self-similar solution for the steady base flow can be obtained at a fixed Dean number. Exploiting the proposed semi-analytic scaling in the stability analysis provides satisfactory results.

Place, publisher, year, edition, pages
Cambridge University Press (CUP), 2024
Keywords
bifurcation, instability
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-347305 (URN)10.1017/jfm.2024.324 (DOI)001231852900001 ()2-s2.0-85194089423 (Scopus ID)
Note

QC 20240612

Available from: 2024-06-10 Created: 2024-06-10 Last updated: 2024-06-12Bibliographically approved
Manami, M., Seddighi, S. & Örlü, R. (2023). Deep learning models for improved accuracy of a multiphase flowmeter. Measurement, 206, 112254, Article ID 112254.
Open this publication in new window or tab >>Deep learning models for improved accuracy of a multiphase flowmeter
2023 (English)In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 206, p. 112254-, article id 112254Article in journal (Refereed) Published
Abstract [en]

Measurement of oil and gas two-phase flow with variable flow regimes relies to a large extent on flow patterns and their transitions. Using multiphase flowmeters in flows with high gas volume fractions is therefore usually associated with large uncertainties. This work presents a dynamic neural network method to measure the flow rate using a nonlinear autoregressive network with exogenous inputs (NARX). Total temperature and total pressure are used as network inputs and the obtained results are compared with a multilayer perceptron (MLP). Comparison between modeling results and the experimental data shows that the NARX network can predict oil and gas flow with variable flow regimes with less error compared to the MLP model, e.g. an absolute average percentage deviation (AAPD) of 0.68% instead of 1.02%. The present work can hence be seen as a proof-of -concept study that should motivate further applications of deep learning models to facilitate enhanced accu-racy in flow metering.

Place, publisher, year, edition, pages
Elsevier BV, 2023
Keywords
Flow metering, Multiphase flow, Fluid mechanics, Deep learning
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-323052 (URN)10.1016/j.measurement.2022.112254 (DOI)000894215000006 ()2-s2.0-85143513423 (Scopus ID)
Note

QC 20230113

Available from: 2023-01-13 Created: 2023-01-13 Last updated: 2023-01-13Bibliographically approved
Andreolli, A., Gatti, D., Vinuesa, R., Örlü, R. & Schlatter, P. (2023). Separating large-scale superposition and modulation in turbulent channels. Journal of Fluid Mechanics, 958, Article ID A37.
Open this publication in new window or tab >>Separating large-scale superposition and modulation in turbulent channels
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2023 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 958, article id A37Article in journal (Refereed) Published
Abstract [en]

The presence of very-large-scale motions in wall-bounded turbulent flows is commonly associated with their footprint in the form of the superposition of the large scales at the wall and the additional amplitude modulation of small-scale near-wall turbulence. These two phenomena are currently understood to be interlinked, with the superposed large-scale velocity gradient causing the modulation of small-scale activity in the proximity of the wall. To challenge this idea, we devise a numerical strategy that selectively suppresses either superposition or amplitude modulation, in an effort to isolate and study the remaining phenomenon. Results from our direct numerical simulations indicate that a positive correlation between the amplitude of the small scales in the near-wall region and the large-scale signal in the outer flow persists even when near-wall large-scale motions are suppressed - i.e. in absence of superposition. Clearly, this kind of correlation cannot be caused by the near-wall large-scale velocity or its gradients, as both are absent. Conversely, when modulation is blocked, the near-wall footprints of the large scales seem to disappear. This study has been carried out on channel flows at friction Reynolds number Re-tau = 1000 in both standard simulation domains and minimal streamwise units (MSUs), where the streamwise fluctuation energy is enhanced. The consistency of the results obtained by the two approaches suggests that MSUs can capture correctly this kind of scale interaction at a much reduced cost.

Place, publisher, year, edition, pages
Cambridge University Press (CUP), 2023
Keywords
turbulence theory, turbulent boundary layers
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-325261 (URN)10.1017/jfm.2023.103 (DOI)000949227800001 ()2-s2.0-85150245546 (Scopus ID)
Note

QC 20230404

Available from: 2023-04-04 Created: 2023-04-04 Last updated: 2023-04-04Bibliographically approved
Perez Martinez, A., Örlü, R., Talamelli, A. & Schlatter, P. (2022). Appraisal of cavity hot-wire probes for wall-shear-stress measurements. Experiments in Fluids, 63(9), Article ID 151.
Open this publication in new window or tab >>Appraisal of cavity hot-wire probes for wall-shear-stress measurements
2022 (English)In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 63, no 9, article id 151Article in journal (Refereed) Published
Abstract [en]

Flush-mounted cavity hot-wire probes have emerged as an alternative to classical hot-wire probes mounted several diameters above the surface for wall-shear stress measurements. They aim at increasing the frequency response and accuracy by circumventing the well-known issue of heat transfer to the substrate that hot-wire and hot-film probes possess. Their use, however, depends on the assumption that the cavity does not influence the flow field. In this study, we show that this assumption does not hold, and that turbulence statistics are modified by the presence of the cavity with sizes that are practically in use. The mean velocity and fluctuations increase near the cavity while the shear stress decreases in its surroundings, all seemingly stemming from the fact that the no-slip condition is not present anymore and that flow reversal occurs. Overall, the energy spectra and the probability density function of the wall shear stress fluctuations indicate a change of nature of turbulence by the presence of the cavity.

Place, publisher, year, edition, pages
Springer Nature, 2022
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-319078 (URN)10.1007/s00348-022-03498-3 (DOI)000853851500001 ()2-s2.0-85139264668 (Scopus ID)
Note

QC 20220926

Available from: 2022-09-26 Created: 2022-09-26 Last updated: 2023-05-29Bibliographically approved
Sujar Garrido, P., Becerra Garcia, M. & Örlü, R. (2022). Efficiency assessment of a single surface dielectric barrier discharge plasma actuator with an optimized Suzen–Huang model. Physics of fluids, 34(4), 047110-047110
Open this publication in new window or tab >>Efficiency assessment of a single surface dielectric barrier discharge plasma actuator with an optimized Suzen–Huang model
2022 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 34, no 4, p. 047110-047110Article in journal (Refereed) Published
Abstract [en]

Spatial and time-resolved characteristics of a single surface dielectric barrier discharge (sDBD) actuator are experimentally and numerically investigated. The paper also focuses on the efficiency of sDBD actuators used as flow-control devices. The motivation is the need for developing a cost-effective way to optimize the balance between control performance and actuator power consumption. The study considers the steady state as often employed in experiments as well as the transient regime. Experimental methods to obtain the active power are revisited, and for the first time, the commonly used simplified phenomenological Suzen–Huang model (SHM) is used for the computation of electrical characteristics. The SHM represents fair qualitative features of the starting vortex. However, it fails when time-resolved velocity profiles are compared. Results show that even with an optimized parametrical analysis of the “tuned” plasma variables, the model is not able to fully reproduce the induced wall-jet neither spatially nor temporally. Furthermore, it underestimates the power consumption by more than 80%. The intrinsic challenge of accurately measuring the alternating current of the DBD and the instantaneous mechanical power, together with the failure of representing time-resolved velocity profiles and the underestimated electric power by the model, highlights that a better phenomenological model including gas dynamics and electric characteristics or using a fully coupled physical plasma model is required.

Place, publisher, year, edition, pages
AIP Publishing, 2022
National Category
Fluid Mechanics and Acoustics Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-311483 (URN)10.1063/5.0087395 (DOI)000788837600018 ()2-s2.0-85128403105 (Scopus ID)
Funder
Swedish Energy Agency, 46344-1
Note

QC 20220524

Available from: 2022-04-28 Created: 2022-04-28 Last updated: 2022-06-25Bibliographically approved
Zarei, A., Seddighi, S., Elahi, S. & Örlü, R. (2022). Experimental investigation of the heat transfer from the helical coil heat exchanger using bubble injection for cold thermal energy storage system. Applied Thermal Engineering, 200, Article ID 117559.
Open this publication in new window or tab >>Experimental investigation of the heat transfer from the helical coil heat exchanger using bubble injection for cold thermal energy storage system
2022 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 200, article id 117559Article in journal (Refereed) Published
Abstract [en]

This study investigates cold thermal energy storage (CTES) using a helical coil heat exchanger modified with bubble injection. One of the effective methods for increasing the heat transfer rate in heat exchangers is using bubble injection. A helical coil heat exchanger is immersed inside a cylindrical water storage tank, where the helical coil is the evaporator of a vapor compression refrigeration cycle (VCRC) and provides the designed cooling. Experimental studies were carried out to examine the impact of bubble injection on Nusselt number, the temperature differences in the storage tank, exergy degradation in the evaporator, and cycle coefficient of performance (COP). The bubbles were injected from the bottom of the storage tank in four different geometries at airflow rates ranging from 3 to 11 L/min. The experimental results of this study revealed that bubble injection could significantly increase the COP and heat transfer rate from the storage tank, as well as the exergy destruction and Nusselt number (Nu). This increase was highly dependent on the geometry and flow rate of the bubble injection. The results also indicated that the bubble injection has an optimal flow rate value, which was 9 L/min in this study. More specifically, the COP of the refrigeration cycle and the Nu number increased by 124% and 452%, respectively, compared to the non-bubble injection mode. Finally, for calculating the outside Nusselt number of the helical coil, an empirical correlation as a function of bubble flow rate and bubble injection angle was proposed.

Place, publisher, year, edition, pages
Elsevier BV, 2022
Keywords
Energy storages, Helical coils, Air bubble injection, Nusselt number, COP improvement
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-305614 (URN)10.1016/j.applthermaleng.2021.117559 (DOI)000712101800001 ()2-s2.0-85116908019 (Scopus ID)
Note

QC 20211206

Available from: 2021-12-06 Created: 2021-12-06 Last updated: 2022-06-25Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1663-3553

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