FG Aerodynamik und Strömungslehre
Refine
Year of publication
Document Type
- Scientific journal article peer-reviewed (132) (remove)
Way of publication
- Open Access (3)
Keywords
- Bore collision (1)
- Centrifugal (1)
- Cylinder (1)
- Direct Numerical Simulation (1)
- Fluid Mechanics (1)
- Instability (1)
- Kolbenring (1)
- Mean Flow (1)
- Mechanism (1)
- Periodical boundary conditions (1)
Institute
BTU
Angular momentum transport and flow organization in Taylor-Couette flow at radius ratio of η=0.357"
(2019)
Cooling silicon photovoltaic cells using finned heat sinks and the effect of inclination angle
(2021)
Effect of the Initial Conditions on the Growth of Thermoelectric Instabilities During Parabolic
(2019)
Enhanced outer peaks in turbulent boundary layer using uniform blowing at moderate Reynolds number
(2022)
Uniform blowing in wall bounded shear flows is well known for its drag reducing effects and has long been investigated ever since. However, many contemporary and former research on this topic has confirmed the drag reducing effect but very less is known regarding
how blowing is effecting the Reynolds stresses at high Reynolds number. Therefore, effect of uniform blowing has been experimentally investigated using Stereo Particle Image Velocimetry (SPIV) measurements in a zero pressure gradient turbulent boundary layer (TBL). The data presented in this literature covers a large range of high Reynolds number flow e.g. Reθ = 7500∼19763 where Reynolds number is based on the momentum thickness. Upstream blowing
was varied from 1%∼6% of free stream velocity and measurements were taken downstream after a short interval. Logarithmic and outer region of the TBL was given special attention in terms of investigating statistics and turbulence properties.
Flow Pattern and Heat Transfer in a Cylindrical Annulus Under 1 g and Low-g Conditions: Experiments
(2018)
The mechanism of localized inertial wave excitation and its efficiency is investigated for an annular cavity rotating with Ω0 . Meridional symmetry is broken by replacing
the inner cylinder with a truncated cone (frustum). Waves are excited by individual longitudinal libration of the walls. The geometry is non-separable and exhibits wave
focusing and wave attractors. We investigated laboratory and numerical results for the Ekman number E ≈ 10−6. inclination α = 5.71◦ and libration amplitudes ε 0.2 within the inertial wave band 0 < ω < 2Ω0 . Under the assumption that the inertial waves do not essentially affect the boundary-layer structure, we use classical boundary-layer analysis to study oscillating Ekman layers over a librating wall that is at an angle α = 0 to the axis of rotation. The Ekman layer erupts at frequency ω = f∗, where f∗ ≡ 2Ω0 sin α is the effective Coriolis parameter in a plane tangential to the wall. For
the selected inclination this eruption occurs for the forcing frequency ω/Ω0 = 0.2. For the librating lids eruption occurs at ω/Ω0 = 2. The study reveals that the frequency dependence of the total kinetic energy Kω of the excited wave field is strongly connected to the square of the Ekman pumping velocity wE (ω) that, in the linear limit, becomes singular when the boundary layer erupts. This explains the frequency dependence of non-resonantly excited waves. By the localization of the forcing, the two configurations investigated, (i) frustum libration and (ii) lids together with outer cylinder in libration, can be clearly distinguished by their response spectra. Good agreement was found for the spatial structure of low-order wave attractors and periodic orbits (both characterized by a small number of reflections) in the frequency windows predicted by geometric ray tracing. For ‘resonant’ frequencies a significantly increased total bulk energy was found, while the energy in the boundary layer remained nearly constant. Inertial wave energy enters the bulk flow via corner beams, which are parallel to the characteristics of the underlying Poincaré problem. Numerical simulations revealed a mismatch between the wall-parallel mass fluxes
near the corners. This leads to boundary-layer eruption and the generation of inertial waves in the corners.