'Energy spectrum for buoyancy-driven turbulence' by Abhishek Kumar (Coventry)

Duration: 33 mins 59 secs

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Description:	Talk given by Dr Abhishek Kumar (Applied Mathematics Research Centre, Coventry University) at Department of Engineering, University of Cambridge, 16 February 2018, as part of the CUED Fluids seminar series. The talk discusses turbulent buoyancy-driven flows, and describes investigations with DNS into the wavenumber scaling of fluxes of kinetic and potential energy for stably-stratified flow and Rayleigh-Benard convection.

Description:

Talk given by Dr Abhishek Kumar (Applied Mathematics Research Centre, Coventry University) at Department of Engineering, University of Cambridge, 16 February 2018, as part of the CUED Fluids seminar series.

The talk discusses turbulent buoyancy-driven flows, and describes investigations with DNS into the wavenumber scaling of fluxes of kinetic and potential energy for stably-stratified flow and Rayleigh-Benard convection.


Created:	2018-02-27 14:39
Collection:	Cambridge Engineering Dept Fluids Seminars
Publisher:	University of Cambridge
Copyright:	Dr Abhishek Kumar
Language:	eng (English)
Keywords:	buoyancy-driven flows; Rayleigh-Benard convection; stably-stratified turbulence; thermal convection; thermally-driven turbulence;


Abstract:	Buoyancy-driven flows are often encountered in geophysics, astrophysics, atmospheric and solar physics, and engineering. In general, these flows come in two categories: stably stratified flows and Rayleigh-Bénard convection (RBC). Turbulent aspects of these flows are an active field of research. An important unsolved problem in this field is how to quantify the small-scale quantities, e.g., spectra and fluxes of kinetic energy (KE) and potential energy (PE) of these flows. Using direct numerical simulations performed at high resolution, we demonstrate that the stably stratified turbulence at moderate stratification exhibits Bolgiano-Obukhov scaling, due to the conversion of kinetic energy to potential energy via buoyancy. We show that the KE flux decreases with the wavenumber (k) which yield k and k^(-7/5) scaling for KE and PE spectra respectively. For RBC , we performed simulation at grid resolution 4096^3 on a cubical box and have shown a delicate balance of dissipation and energy supply rate by buoyancy. This balance leads to a constant KE flux and rules out the Bolgiano-Obukhov scaling, and we observe Kolmogorov’s spectrum [1-3]. References: [1] Kumar, Chatterjee, and Verma, Phys. Rev. E, 90, 023016 (2014). [2] Kumar and Verma, Phys. Rev. E, 91, 043014 (2015). [3] Verma, Kumar, and Pandey, New J. Phys., 19, 025012 (2017).

Abstract:

Buoyancy-driven flows are often encountered in geophysics, astrophysics, atmospheric and solar physics, and engineering. In general, these flows come in two categories: stably stratified flows and Rayleigh-Bénard convection (RBC). Turbulent aspects of these flows are an active field of research. An important unsolved problem in this field is how to quantify the small-scale quantities, e.g., spectra and fluxes of kinetic energy (KE) and potential energy (PE) of these flows. Using direct numerical simulations performed at high resolution, we demonstrate that the stably stratified turbulence at moderate stratification exhibits Bolgiano-Obukhov scaling, due to the conversion of kinetic energy to potential energy via buoyancy. We show that the KE flux decreases with the wavenumber (k) which yield k and k^(-7/5) scaling for KE and PE spectra respectively. For RBC , we performed simulation at grid resolution 4096^3 on a cubical box and have shown a delicate balance of dissipation and energy supply rate by buoyancy. This balance leads to a constant KE flux and rules out the Bolgiano-Obukhov scaling, and we observe Kolmogorov’s spectrum [1-3]. References: [1] Kumar, Chatterjee, and Verma, Phys. Rev. E, 90, 023016 (2014). [2] Kumar and Verma, Phys. Rev. E, 91, 043014 (2015). [3] Verma, Kumar, and Pandey, New J. Phys., 19, 025012 (2017).

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