Search results for "Curved pipe"

Transition to turbulence in toroidal pipes

2011

AbstractIncompressible flow in toroidal pipes of circular cross-section was investigated by three-dimensional, time-dependent numerical simulations using a finite volume method. The computational domain included a whole torus and was discretized by up to ${\ensuremath{\sim} }11. 4\ensuremath{\times} 1{0}^{6} $ nodes. Two curvatures $\delta $ (radius of the cross-section/radius of the torus), namely 0.3 and 0.1, were examined; a streamwise forcing term was imposed, and its magnitude was made to vary so that the bulk Reynolds number ranged between ${\ensuremath{\sim} }3500$ and ${\ensuremath{\sim} }14\hspace{0.167em} 700$. The results were processed by different techniques in order to confirm…

Turbulence structure and budgets in curved pipes

2013

Abstract Turbulent flow in curved pipes was investigated by Direct Numerical Simulation. Three curvatures δ (pipe radius a /curvature radius c ) were examined: δ  = 0 (straight pipe), simulated for validation and comparison purposes; δ  = 0.1; and δ  = 0.3. The friction velocity Reynolds number (based on the pipe radius a ) was 500 in all cases, yielding bulk Reynolds numbers of ∼17,000, ∼15,000 and ∼12,000 for δ  = 0, 0.1 and 0.3, respectively. The computational domain was ten pipe radii in length and was resolved by up to 20 × 10 6 hexahedral finite volumes. The time step was chosen equal to a wall time unit; 1 Large Eddy TurnOver Time (LETOT) was thus resolved by 500 time steps and simul…

Simulazioni Numeriche del Campo di Moto e della Caduta di Pressione in Tubi Elicoidali

2009

Direct numerical simulation of turbulent heat transfer in curved pipes

2012

Fully developed turbulent convective heat transfer in curved pipes was investigated by Direct Numerical Simulation for a friction velocity Reynolds number of 500, yielding bulk Reynolds numbers between 12 630 and ~17 350 according to the curvature (pipe radius/curvature radius). Three different curvatures were compared, i.e. 0 (straight pipe), 0.1 and 0.3. The Prandtl number was 0.86. The computational domain was a tract of pipe 5 diameters in length. A finite volume method was used, with multiblock structured grids of ~5.3x10E6 hexahedral volumes. Simulations were typically protracted for 20 LETOT’s starting from coarse-grid results. Results were post-processed to compute first and second …

On the influence of gravitational and centrifugal buoyancy on laminar flow and heat transfer in curved pipes and coils

2015

Abstract The effects of gravitational and centrifugal buoyancy on laminar flow and heat transfer in curved and helical pipes were investigated by numerical simulation. Six dimensionless numbers characterizing the problem were identified, and an analysis was conducted on the possible combinations of signs of the gravitational and centrifugal buoyancy effects. Two distinct Richardson numbers were introduced in order to quantify the importance of the two types of buoyancy, and it was shown that, in the case of heating from the wall, a maximum realizable value of the centrifugal Richardson number exists which is a linear function of the curvature δ (ratio of pipe radius a to curvature radius c)…

Fully developed laminar flow and heat transfer in serpentine pipes

2015

Abstract A serpentine pipe is a sequence of parallel straight pipe segments connected by U-bends. Its geometry is fully characterized by pipe radius, a , bend curvature radius, c and length of the straight segments, l . The repeated curvature inversion forces the recirculation (secondary flow) pattern to switch between two specular configurations, which may enhance mixing and heat or mass transfer with respect to a constant-curvature pipe at the cost of an increase in pressure drop. In the present work, fully developed laminar flow and heat transfer in serpentine pipes were investigated by numerical simulation. The curvature δ  =  a / c was made to vary between 0.1 and 0.5 while the paramet…

A study of turbulent heat transfer in curved pipes by numerical simulation

2013

Abstract Turbulent heat transfer in curved pipes was studied by numerical simulation. Two curvatures δ (pipe radius a/curvature radius c) were considered, 0.1 and 0.3; results were also obtained for a straight pipe (δ = 0) for comparison purposes. A tract of pipe 5 diameters in length was chosen as the computational domain and was discretized by finite volume multiblock-structured grids of ∼5.3 × 106 hexahedral cells. Fully developed conditions were assumed; the friction velocity Reynolds number was 500, corresponding to bulk Reynolds numbers between 12 630 and ∼17 350 according to the curvature, while the Prandtl number was 0.86 (representative of saturated liquid water at 58 bar). Simulat…

Steady, periodic, quasi-periodic and chaotic flow regimes in toroidal pipes

2012

Incompressible flow in a toroidal pipe was investigated by direct numerical simulation. The curvature a/c (radius of the cross section / radius of the torus) was 0.3 or 0.1 and the bulk Reynolds number ranged between 3500 and 14 700. The study revealed a rich scenario of transition to turbulence. For the higher curvature a/c = 0.3, a supercritical transition from stationary to periodic flow (Hopf bifurcation) was observed at Re=4600. The periodic flow was characterized by a travelling wave which, in the whole periodic Re range, took the form of a varicose modulation of the twin Dean vortex rings, included 8 wavelengths along the axis of the torus, and exhibited instantaneous anti-symmetry a…