10:30
Control 1
Chair: Blair Perot
10:30
15 mins
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EXPERIMENTAL INVESTIGATION OF TURBULENT BOUNDARY LAYER FLOW UNDERGOING SPANWISE TRAVELING TRANSVERSAL SURFACE WAVES
Dorothee Roggenkamp, Wenfeng Li, Wilhelm Jessen, Michael Klaas, Wolfgang Schröder
Abstract: The influence of spanwise traveling transversal surface waves on the near-wall flow field of turbulent boundary layers with and without adverse pressure gradient is investigated by particle-image velocimetry (PIV) and micro-particle tracking velocimetry (μ-PTV). A detailed analysis of the velocity profile immediately downstream of the actuated surface shows a local drag decrease as well as an increase caused by the surface wave dependent on the wave parameters.
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10:45
15 mins
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Tuning Transitions in Rotating Rayleigh-Bénard Turbulence
Pranav Joshi Joshi, Rudie Kunnen, Herman Clercx
Abstract: Rayleigh-Bénard convection is a canonical system for the investigation of buoyancy-driven natural convection phenomena which abound in nature and technology. Under the influence of rotation and depending on the system parameters, the flow exhibits different regimes with disparate heat transfer characteristics even in the turbulent state. The present study attempts to tune the transitions between these regimes and thus control the heat transfer in practical applications. In particular, we explore the effect of addition of neutrally-buoyant thermally-conducting particles to the fluid. Following an experimental approach, we study the flow structure and heat transfer as functions of particle concentration and system parameters.
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11:00
15 mins
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Turbulence statistics of turbulent boundary layer flow following injection of drag-reducing surfactant solution
Shinji Tamano, Jun Ito, Hiroki Uchikawa, Yohei Morinishi
Abstract: To investigate streamwise variations of turbulence statistics in the wide range of the drag reduction ratio for the zero-pressure-gradient turbulent boundary layer flow due to the injection of drag-reducing nonionic surfactant solutions, we performed the laser-Doppler velocimetry (LDV) measurement at a new experimental apparatus with the larger size than previous one. The drag reduction ratio up to 76% could be obtained, at which the mean velocity in wall-units was beyond the Virk's ultimate for polymer solutions.
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11:15
15 mins
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Effect of linear feedback control on the optimal transient growth in particle-laden channel flow
Yang Song, Chun xiao Xu, Wei xi Huang
Abstract: The optimal transient growth process in a particle-laden channel flow is studied under the influence of the linear feedback control. The equilibrium Eulerian approach with the assumption that the particles are small and spherical is adopted. The effect of initial distribution of particles on the optimal transient growth of perturbations is discussed. The LQG control of the particle-laden flow system is considered and compared with the no control cases.
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11:30
15 mins
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EXPERIMENTAL OBSERVATION OF DIFFERENT INTERMITTENCY TYPES IN SPHERICAL COUETTE FLOW
Dmitry Zhilenko, Olga Krivonosova
Abstract: Flows between concentric, counter rotating spherical boundaries are under investigation in a gap with a size equal to the inner sphere radius. The outer sphere rotational rate is fixed, while the inner sphere rotational rate was modulated. The amplitudes and frequencies of modulation are small relative to the averaged rotational rates of both spheres. With modulation amplitude increase, a transition from initial periodical flow to chaos occurs. To determine the state of the flow, time series of azimuthal velocity were used. Measurements were carried out by laser Doppler anemometer. Flow states with chaos–chaos and cycle–chaos–chaos intermittency were detected. The quantitative characteristics are considered, which allow separate different
patterns of the flow state with distinct properties.
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11:45
15 mins
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DNS OF TRANSITION TO NONUNIFORM IN TIME AND/OR SPACE TURBULENT FLOWS IN ROTATING SPHERICAL LAYERS
Dmitry Zhilenko, Olga Krivonosova
Abstract: We have numerically studied the transition to turbulence in a layer of a viscous incompressible fluid confined between concentric counter rotating spherical boundaries. Rotational speeds of one or two boundaries were periodically modulated. The transition to turbulence was caused by an increase in the modulation amplitude. Two different cases of transitions were under consideration. In the first case modulation of outer sphere velocity with constant inner sphere speed was imposed on initial periodical flow state. The obtained solutions reveal cycle-chaos intermittency type - irregular temporal alternation of laminar and turbulent states occupying the whole layer. In the second case both of spheres were opposite-phase oscillated at the same frequency and amplitude about the state of rest. The obtained solutions exhibits chaos-chaos intermittency type of the flow - irregular temporal alternation of weak and strong turbulent states in the limited part of the layer, outside which the flow remains periodical.
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12:00
15 mins
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TURBULENT DRAG REDUCTION USING WALL JETS AT FLIGHT SCALE REYNOLDS NUMBER
Faisal Baig, Farhan Khan
Abstract: Numerical experiments have been performed for modelling turbulent drag reduction due to active-control of wall jets using a linearised Navier-Stokes model in a turbulent boundary layer formed over a flat plate at Re _τ = 905 corresponding to flight scale Re_x = 10^6 . Its effect have been seen on transient growth of near-wall streaks and production of turbulent kinetic energy (TKE). Two sets, one corresponding to span wise slot and other corresponding to wall jets along the whole plate have been performed. Simulations
are performed by varying magnitude of wall jets, its angle & locations and based on a measure of TKE, reduction in stream wise turbulent kinetic energy is recorded.
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