Developed Pipe Flow Research Articles

Large-Eddy simulation of an impinging heated jet for a small nozzle-to-plate distance and high Reynolds number

This paper reports on the investigation of an original impinging jet configuration through a wall-resolved large-eddy simulation. The heated jet issues from a fully developed pipe flow at temperature of 130 °C and a Reynolds number based on the bulk velocity of 60000. The impinged plate is located three diameters downstream of the pipe exit. The CFD results have been validated against a specifically-created experimental database (Grenson et al., 2016). The overall statistical fields are well retrieved by the simulation both in the free jet and the wall jet region. In particular, the secondary maximum at the radial location r/D=2 in the Nusselt number distribution is well predicted by the simulation. The underlying mechanisms from which the secondary maximum originates has been investigated. This analysis revealed that small-scale hot spots of strong convective heat transfer coefficient are responsible for the emergence of this secondary maximum. It is shown that the hot spots can be associated either to local unsteady “separation” of the flow or streaks-like structures above the impinging plate.

Empirical models for liquid metal heat transfer in the entrance region of tubes and rod bundles

Experiments focusing on liquid metals heat transfer in pipes and rod bundles with thermally and hydraulically developing flow are reviewed. Empirical heat transfer correlations are developed for engineering applications. In the developing regions the heat transfer is in-stationary. The heat transfer at the entrance is around 100 % higher due to the developing process including the lateral exchange of energy and momentum than for developed flow. Developing flow is not physically considered in the framework of system codes, which are used for thermal–hydraulic analysis of power and process plants with a multitude of components like pipes, tanks, valves and heat exchangers. Therefore, the application to liquid metal flows is limited to developed flow, which is independent of the distance from the flow entrance. The heat transfer enhancement in developing flows is important for the optimization of components like heat exchangers and helps to reduce unnecessary conservatism. In this work, empirical models are developed to account for developing flows in pipes and rod bundles. A literature review is performed to collect available experimental data for developing flow in liquid metal heat transfer. The evaluation shows that the length for pure thermally developing pipe flow is much larger (20–30 hydraulic diameters) than for combined thermally and hydraulically developing flow (10–15 hydraulic diameters). In rod bundles, fully combined developed flow is established after 30–40 hydraulic diameters downstream of the entrance. The derived empirical models for the heat transfer enhancement in the developing regions are implemented into a best estimate system code. The validation of these models by means of post-test analyses of 16 experiments shows that they are very well able to represent the heat transfer in developing regions.

Numerical study of the internal flow field of a dual pulse solid rocket motor including conjugate heat transfer

Numerical simulations were performed to study the influence of the inside diameter of the pulse separation device port on the flow features and the local heat transfer characteristics in a dual pulse solid rocket motor. A lower–upper symmetric Gauss–Seidel implicit dual time-stepping method was applied to address the problem of unsteady flow. A high-resolution upwind scheme (AUSMPW+) and Menter’s shear stress transport turbulence model were employed to solve the Reynolds-averaged Navier–Stokes equations. The conjugate heat transfer strategy was realized by enforcing a common temperature and heat flux at the fluid–solid interface. After validating the accuracy and reliability of the numerical algorithm by comparison with experimental cases, the internal flow of a dual pulse solid rocket motor was simulated. The results show that the magnitude of the velocity, the wall shear stress, and the turbulent kinetic energy downstream of the pulse separation device port decrease with increasing pulse separation device port diameter. The local heat transfer coefficient increases sharply downstream of the pulse separation device port, reaching a maximum within 1–2 diameters downstream of the pulse separation device port, before relaxing back to the fully developed pipe flow value. The peak value of the local heat transfer coefficient reduces as the pulse separation device port diameter increases. Meanwhile with an increasing pulse separation device port diameter, the position of the peak local heat transfer coefficient moves upstream to the head of the first pulse chamber, and appears upstream of the position of the reattachment point by an average of about 28.6%.

Relaminarization of wall turbulence by high-pressure ramps at low Reynolds numbers

Reverse transition from the turbulent towards the laminar flow regime was investigated experimentally by progressively increasing the pressure up to 400 MPa in a fully developed pipe flow operated with silicone oil as the working fluid. Using hot-wire anemometry, it is shown indirectly that at low Reynolds numbers a rapid increase in pressure modifies the turbulence dynamics owing to the processes which induce the effects caused by fluid compressibility in the region very close to the wall. The experimental results confirm that under such circumstances, the traditional mechanism responsible for self-maintenance of turbulence in wall-bounded flows is altered in such a way as to lead towards a state in which turbulence cannot persist any longer.

Numerical Investigation of Turbulent Mass Transfer in a 90° Bend

This paper presents a numerical study of local mass transfer coefficients in a 90° bend using the RNG version of k–e model to include the influence of curvature on the turbulent transport. Simulations were performed for flow through a 90°, 3-D bend for Reynolds numbers of 13500, 90000, and 390000, Schmidt numbers of 2.53 and 700 and curvature ratios of 1.5, 2, and 2.5. The differences between the maximum axial velocity to average velocity (Umax/Uave) predicted by the model and the experimental results reported in the literature was generally less than two percent. Simulation results showed that the ratio of the maximum Sherwood number obtained in the elbow to that obtained in fully developed pipe flow (Sh/Shp) decreased by Reynolds number (Re), Schmidt number (Sc) and curvature ratio (r/D). Maximum local mass transfer coefficient was observed at a distance of about one diameter downstream of the 90° elbow. Numerical predictions were in good agreement with experimental results reported in the literature.

Transport of micro-bubbles in turbulent shear flows

The dynamics of micro-bubbles, which are typical in many industrial applications, is addressed by means the Direct Numerical Simulations (DNS) of two prototypal flows, namely a homogeneous shear flow and a fully developed pipe flows. This preliminary study has a two-fold purpose. The homogenous turbulent shear flow is useful to characterize the bubble dynamics in terms of their eventual clustering properties which is expected to be controlled by the Stokes number. The time history of the fluid pressure experienced by the bubbles during their evolution is recorded and successively employed to force the Rayleigh-Plesset equation [1]. The ensuing data are used to address a posteriori the bubble diameter statistics in view of bubble collapse induced by strong and intermittent turbulent pressure fluctuations. The turbulent pipe flow simulations serve to address the bubble dynamics in wall bounded flows. Here the bubbles are observed to accumulate in the near-wall region with different intensity depending on the bubble dimensions.

Friction factor and mean velocity profile for pipe flow at high Reynolds numbers

The friction factor for a fully developed pipe flow is examined at high Reynolds numbers up to ReD = 1.8 × 107 with high accuracy using the high Reynolds number actual flow facility “Hi-Reff” at AIST, NMIJ. The precise measurement of the friction factor is achieved by the highly accurate measurement of the flow rate, and the measurement uncertainty is estimated to be approximately 0.9% with a coverage factor of k = 2. The result examined here is obviously different from the Prandtl equation and the experimental results from the superpipe at Princeton University. The deviation of the present result from the Prandtl equation in the lower Reynolds number region is approximately 2.5% and −3% at the higher Reynolds number. For ReD < 2.0 × 105, the present friction factor obtained here agrees very well with the results at the superpipe, but a deviation is observed for ReD > 2.0 × 105, and it increases with the Reynolds number and reaches −6% at ReD = 1.0 × 107. The Kármán constant estimated by the measured friction factor is 0.385. Using inner scale variables estimated by the present friction factor, the velocity profile measured by laser Doppler velocimetry in the same measurement configuration for the friction factor is normalized in order to observe the consistency of the Kármán constants between both the measurements. The Kármán constant estimated by the measured velocity profiles for ReD > 3.0 × 105 is 0.382.

Large-Eddy Simulations of Wall Bounded Turbulent Flows Using Unstructured Linear Reconstruction Techniques

Large-eddy simulations (LES) of wall bounded, low Mach number turbulent flows are conducted using an unstructured finite-volume solver of the compressible flow equations. The numerical method employs linear reconstructions of the primitive variables based on the least-squares approach of Barth. The standard Smagorinsky model is adopted as the subgrid term. The artificial viscosity inherent to the spatial discretization is maintained as low as possible reducing the dissipative contribution embedded in the approximate Riemann solver to the minimum necessary. Comparisons are also discussed with the results obtained using the implicit LES (ILES) procedure. Two canonical test-cases are described: a fully developed pipe flow at a bulk Reynolds number Reb = 44 × 103 based on the pipe diameter, and a confined rotor–stator flow at the rotational Reynolds number ReΩ = 4 × 105 based on the outer radius. In both cases, the mean flow and the turbulent statistics agree well with existing direct numerical simulations (DNS) or experimental data.

Flow Regimes and Heat Transfer Characteristics in Combustion Chambers

This paper presents a numerical computations are performed to investigate the convective heat transfer characteristics of a gas turbine can combustor under non reacting flow conditions in a Reynolds number range 50,000 to 600,000 with a characteristic swirl number of 0.7. A sample of computational predictions of flow behaviors under reacting conditions are also shown for swirling furnace flow of 0.52. The RNG (K-ɛ Model) predictions are compared with the experimental data of local heat transfer distribution on the combustor liner wall. It was observed that the flow field in the combustor is characterized by an expanding swirling flow, which impinges on the liner wall close to the inlet of the combustor. The peak heat transfer augmentation ratio (compared with fully developed pipe flow) reduces from 10.5 to 2.7. Additionally, the peak location does not change with Reynolds number since the flow structure in the combustor is also a function of the swirl number. The size of the corner recirculation zone near the combustor liner remains the same for all Reynolds numbers and hence the location of shear layer impingement and peak augmentation does not change. The heat transfer coefficient distribution on the liner wall predicted from the RNG (K-ɛ Model) is in good agreement with experimental values. The location and the magnitude of the peak heat transfer are predicted in very close agreement with the experiments.

The CoLaPipe--the new Cottbus large pipe test facility at Brandenburg University of Technology Cottbus-Senftenberg.

The CoLaPipe is a novel test facility at the Department of Aerodynamics and Fluid Mechanics, Brandenburg University of Technology Cottbus-Senftenberg (BTU Cottbus-Senftenberg), set up to investigate fully developed pipe flow at high Reynolds numbers (Re(m) ⩽ 1.5 × 10(6)). The design of the CoLaPipe is closed-return with two available test sections providing a length-to-diameter ratio of L/D = 148 and L/D = 79. Within this work, we introduce the CoLaPipe and describe the various components in detail, i.e., the settling chamber, the inlet contraction, the blower, bends, and diffusers as well as the cooling system. A special feature is the numerically optimized contraction design. The applications of different measuring techniques such as hot-wire anemometry and static pressure measurements to quantitatively evaluate the mean flow characteristics and turbulence statistics are discussed as well. In addition, capabilities and limitations of available and new pipe flow facilities are presented and reconsidered based on their length-to-diameter ratio, the achieved Reynolds numbers, and the resulting spatial resolution. Here, the focus is on the facility design, the presentation of some basic characteristics, and its contribution to a reviewed list of specific questions still arising, e.g., scaling and structural behavior of turbulent pipe flow as well as the influence of the development length on turbulence investigations.

Mass transfer in dual pipe bends arranged in an S-configuration

The mass transfer in dual in-plane short radius bends arranged in an S-configuration was measured for different separation distances (L/D) between the two bends. Experiments were performed using a wall dissolution technique with gypsum test sections at a Schmidt number (Sc) of 1280 for L/D from 0 to 5 at a Reynolds number (Re) of 70,000. The maximum mass transfer was found to occur between the outlet of the first bend outer wall and the inlet of the second bend inner wall in all cases. The maximum mass transfer occurred for L/D=0 and was 3.2 times larger than the average mass transfer in a fully developed pipe flow under the same flow condition. The maximum mass transfer decreased as the separation distance between the two bends was increased. The effect of Re on the mass transfer enhancement for a separation distance of L/D=0 was examined for Re in the range 40,000–130,000. The peak mass transfer was found to scale as Re0.93 and was similar to that of the peak mass transfer in a single bend.

SIMULATION OF DISCRETE BLOOD VESSEL EFFECTS ON THE THERMAL SIGNATURE OF A MELANOMA LESION.

The effect of the underlying blood vessel on the transient thermal response of the skin surface with and without a melanoma lesion is studied. A 3D computational model of the layers of the skin tissue with cancerous lesion was developed in COMSOL software package. Heat transfer in the skin layers and the lesion is governed by the Pennes bio-heat equation, while the blood vessel is modeled as fully developed pipe flow with constant heat transfer coefficient. The effect of various pertinent parameters, such as diameter of the blood vessel, lateral location of the blood vessel relative to the lesion, flow velocity of the blood, on the skin surface temperature distribution, have been studied in the paper. The results show significant influence of the underlying blood vessel on the temperature of the skin surface and lesion as well as on the surrounding healthy tissue. Thus, a need for development of evaluation criteria for detection of malignant lesions in the presence of blood vessels is is discussed.

Numerical investigation on mass transfer enhancement downstream of an orifice

Mass transfer enhancement is an indispensible element in flow accelerated corrosion (FAC). In order to investigate mass transfer enhancement downstream of an orifice, the two-dimensional computational fluid dynamics (CFD) calculation is conducted. First, validation of turbulence model, the ζ–f model, is conducted in the fully developed pipe flow, the flow through an orifice and the flow downstream of a sudden expansion. The validation shows that the model is adequate to predict mass transfer enhancement in all the tested flows. Effects of Reynolds number, orifice thickness and diameter ratio on mass transfer enhancement downstream of an orifice are then investigated based on the numerical calculation. The investigation shows that the mass transfer enhancement ratio decreases with the increasing Reynolds number. However, the locations of reattachment point and the peak transfer rate point are not affected by the Reynolds number. Parametric study on the orifice thickness shows that a thin orifice helps mass transfer enhancement in its downstream. This is attributed to more intense turbulence generation downstream of a thin orifice. Moreover, the peak transfer point appear about 0.4Lr (reattachment length) downstream of the orifice. The results of the parametric study are synthesized as a correlation,StmaxStfd=4.78Re-0.12dD-1.161+0.82(L1/d)31+(L1/d)3which is expected to be valid in the range of 4.2×104⩽Re⩽1.3×105, 0.4⩽d/D⩽0.75, 0.13⩽L1/d⩽2.61.

Experimental and numerical studies on mass transfer characteristics behind an orifice in a circular pipe for application to pipe-wall thinning

Experimental and numerical studies are carried out to understand the mass transfer characteristics in a circular pipe behind an orifice, which is often encountered in pipe-wall thinning due to flow accelerated corrosion in pipelines of nuclear/fossil power plants. The measurement of mass transfer coefficient is conducted by using benzoic acid dissolution method in a water flow, which allows the measurement of mass transfer behind the orifice in a circular pipe at the Schmidt number near the actual operating condition of the pipeline. The measurement of mass transfer coefficient behind the orifice shows a maximum Sherwood number in the region 1–2 pipe diameters downstream of the orifice due to the flow turbulence, and it decreases gradually in the downstream, which agrees qualitatively with the feature of pipe-wall thinning in the pipeline in literature. The present result indicates that the Sherwood number behind the orifice is greatly increased by increasing the Schmidt number and the Reynolds number, though the geometrical factor, which is the ratio of the thinning rate of the orifice flow with respect to that of the fully developed pipe flow, is weakly dependent of these parameters. It is also found that the experimental Sherwood number profiles and the mean velocity distribution behind the orifice are well reproduced in the numerical simulation by the k–ε model with the empirical modification of high-Schmidt-number flows, though the maximum Sherwood number is slightly overpredicted, reflecting the higher prediction of turbulence energy behind the orifice. These results demonstrate the usefulness of the numerical simulation for predicting the pipe-wall thinning due to the flow accelerated corrosion in the orifice flow.

Numerical Simulation on the Flow Field inside an Ultrasonic Water Meter

Flow field inside an ultrasonic water meter of time-difference-type are numerically simulated at several flow rates. Linear mean velocity (LMV) averaged along the line between the transmitting transducer and the receiving one, and the surface mean velocity (SMV) averaged in the cross section of the reducing-type flow passage, and the flow correction coefficient are calculated with the flow field data obtained by the simulation. Its found that the values of flow correction coefficient for the reducing-type meter channel flow are quite different from that for a fully developed pipe flow, and are related to the flow rate or Reynolds number.

Particle image velocimetry measurements of flow field behind a circular square-edged orifice in a round pipe

In this paper, we use a planar particle image velocimetry system to measure the flow field downstream of a circular square-edged orifice plate in a round pipe. The flow field is a fully developed pipe flow well upstream of the orifice plate. The Reynolds number based on pipe diameter and cross-sectional mean velocity is in the range of 25,000–55,000. We present detailed mean and turbulent fields and investigate similarities and differences with other separated flows. A noteworthy difference is the formation of a vena contracta behind the orifice at a distance of approximately one pipe radius. Upstream of the vena contracta, the properties of the shear layers in the orifice flow are quite similar to those of other separated flows. However, because the shear layer in the orifice flow begins to merge at a distance of approximately one pipe diameter, it is significantly different from the shear layers in other separated flows. Finally, we assess the reliability of the Reynolds stress model to represent orifice flows by comparing numerical results with experimental results.

Effectiveness of Perforated Plate in the Development and Establishment of Turbulent Flow for Better Metrological Performances

numbers 10 4 , 10 5 and 10 6 . The code used was fluent v6.3, where the Navier-Stokes equations are solved by the finite volume method with k-e like a turbulent model. Validation of numerical predictions for the velocity profiles, turbulence intensity and the gyration angle of the fluid is made according to ISO 5167. The results obtained show the effectiveness of the perforated plate in the development and the establishment of the turbulent flows towards the fully developed pipe flow wish is a necessary condition for flow measurement accuracy. We also note, from the results, that the flow needs more 30D of distance to reach better metrological performances.

Characterisation of gas mixing in water and pulp-suspension flow based on electrical resistance tomography

Gas dispersion in horizontal developing pipe flow downstream of a 90°-tee mixer and an in-line mechanical mixer was investigated by means of electrical resistance tomography (ERT) for both water and softwood kraft pulp suspensions over a range of fibre mass concentrations (0–3.0%), superficial liquid/pulp velocities (0.5–5.0m/s) and superficial gas velocities (0.11–0.44m/s). A gas mixing index, derived from the standard deviation of local gas holdup in each image pixel, quantified the uniformity of gas in cross-sectional planes along the pipe for various flow patterns. The distribution of the gas phase in a cross-section was determined from the vertical gas holdup profiles, and the relative size of gaseous entities for different flow conditions was evaluated based on the scale of segregation. For air–water flow, the gas uniformity and size of gaseous entities depended strongly on the flow pattern. For pulp fibre suspensions, the gas flow varied significantly depending on the flow regime. Mixing was similar to that in water when the flow was turbulent for dilute suspensions, but differed greatly for higher mass concentrations, likely due to robust fibre networks of a plug in the core of the pipe causing bubbles to concentrate near the wall and accelerating coalescence. The impeller disrupted the plug and distributed gas throughout the cross-section, leading to significantly improved gas uniformity in the high-shear zone around the impeller, but decaying turbulence and re-establishment of fibre networks caused bubbles to coalesce at the top of the pipe and worse mixing downstream.

Quantifying diatom aspirations: Mechanical properties of chain‐forming species

Diatoms developed a variety of mechanisms to form chain‐like colonies, resulting in diverse morphologies and bulk mechanical properties. These properties affect translation, rotation, and deformation of colonies in ambient flows as well as their susceptibility to breakage by flow‐ and grazer‐induced forces. Morphological characteristics of diatom chains have been extensively studied, yet no studies have examined their mechanical properties. We studied the flexibility of four morphologically distinct species (Lithodesmium undulatum, Stephanopyxis turris, Lauderia annulata, and Guinardia delicatula) by measuring their deflections when held across a capillary tip in developing pipe flow and applying simple beam theory and a finite‐difference analysis of curvature to calculate flexural stiffness. Flexural stiffness varies greatly, with at least four orders of magnitude difference among the examined species (from 1.7 × 10−13 N m2, the most rigid, to 1.3 × 10−17 N m2, the most flexible), but two other species (Melosira nummuloides and a Thalassiosira sp.) were too flexible to measure with our apparatus. Vulnerability to breakage by flow also varied between species and, for species with heavily silicified joints between cells, was enhanced under nutrient depletion. These results highlight yet another attribute underlying the biodiversity of diatoms and their potential for utilizing highly differentiated ecological niches. Quantitative information from this study can now be used in the design of more mechanically realistic models that capture the dynamic coupling between elastic particles and flow to study diatom–flow interactions and their effects on nutrient acquisition, encounter with grazers, aggregate formation, and settling.

Analysis of Turbulent Flow Development Downstream Disturbers with Perforated Plate Flow Conditioner

This article discusses the development and the establishment of turbulent flow downstream of disturbers like a valve 50% open, valve 70% open, Tee and 90° double bend in perpendicular planes. Associated with these disturbers, a perforated plate flow conditioner is installed to examine his performances to produce the fully developed pipe flow as suggested by standards ISO5167 and AGA3. The study focused mainly on the numerical analysis of the velocity contours at several axial stations downstream the disturbers. For the simulation, code CFD Fluent was used. The study of the disturbed flow is examined with three Reynolds numbers. The results show a very good prediction of the CFD code Fluent for the flow development downstream the disturbers and conditioner which makes the code very efficient for conception of a new flow conditioner not described by the standards. It was also found that the valve 50% open could be considered a reference disturber for analyzing the development of turbulent flows. As interesting results, is the effectiveness of the perforated plate to produce the flow developed pipe flow at about z/D=10 downstream the disturber. This result is very important for flow measurement accuracy as suggested by the standards. An experimental study is needed to validate these results.