Reynolds Range Research Articles

Experimental Investigation on Laminar Separation Bubble Over an Airfoil � a Review

Objectives: To provide comprehensive literature survey of laminar separation bubble over a low Reynolds number airfoil with reference to the conventional and non-conventional experimental technique using wind tunnel. Methods/ Statistical Analysis: For more convenient understanding, the various wind tunnel experimental techniques and advanced research progress in this field is presenting in table format. The table shows characteristics of laminar separation bubble over airfoil at different Reynolds number for various conditions. The table critiques the proof-based entire data about the Laminar Separation Bubble (LSB) traits (height and period), go with the flow traits differentiated, transition and reattachment locations and go with the flow visualization over airfoil were experimentally discovered at various angles of attack and Reynolds range, respectively. Findings: The current evidence supports the view that laminar separation bubble characteristics, behaviour and its effect over an airfoil. Most studies in this field have been done experimentally using Wind Tunnel with various techniques i.e., Surface Oil Flow Technique, Particle Image Velocimetry (PIV), Infrared Thermography (IT), Force Measurement and Hot-Wire Experiments, Smoke-Wire Experiment, Multi-line Molecular Tagging Velocimetry, Volumetric Three-Component Velocimetry (V3V), Time-resolved surface pressure sensor arrays, ESP (Electronically Scanned Pressure), Embedded Laser Doppler Velocimetry (ELDV), Fast Fourier Transform (FFT). Application/ Improvements: This paper describes the various techniques and characteristics of LSB which will be beneficial to design the low Reynolds number airfoil in order to minimize the drag and increases the aerodynamic efficiency for industrial applications. Keywords: Flow Visualization Techniques, Low Reynolds Number, Laminar Separation Bubble Characteristics, Wind Tunnel Experiments

Неинтрузивное измерение температуры потоков жидкости с использованием трубопроводных компенсаторов

The article presents the results of a numerical study that aimed to accuracy improvement for non-intrusive measurements of the liquid flow temperatures in standard pipelines compensators. Non-intrusive measuring devices are one of the modern promising and profitable tools that stimulate the improvement of technologies and the involvement of world corporations in this sphere, while the growing intellectualization of measurements positively affects the safety and efficiency of the industry. The numerical study result is consistent with the results of laboratory tests and shows the general regularity of flow velocity effect the error of non-intrusive temperature measurements. Shown that measurements after the upper or lower elbow of the compensator makes possible to reduce the measurement error in the Reynolds (Re) range of about 1000–7000, which is characteristic for the onset of turbulent flow of a liquid. Also shown that gravity negatively affects the accuracy of measurements, so preference should be given to horizontally located compensators. Obtained that the flow in pipeline determines the largest temperature change in the wall region of the pipe for relatively high Re, and along the pipeline axis for small Reynolds numbers. In combination with the flow characteristics in the compensator, it changes temperature distribution and error, depending on the flow velocity in the pipeline. In particular, this effect determines error decreasing for temperature measurement in the compensators at low Re numbers. The existing surface temperature sensors, with correction the surface temperature measurements to the flow temperature, require calibration to work on flows with Re numbers varying over a wide range, and binding these measurements to pipeline compensators can improve the quality of measurements due to smoothing and, fluctuation thermal and hydrodynamic influences.

The role of insert devices on enhancing heat transfer in a flat-plate solar water collector

This work presents a comparative experimental study of heat transfer enhancement in a flat-plate solar water collector using insert devices. Three wire-coils and three twisted-tapes were selected with representative geometrical characteristics typically employed in industrial applications. Isothermal pressure drop tests were carried out to obtain the fully-developed Fanning friction factor for a range of Reynolds numbers Re = [80–9000]. The increase in friction factor in comparison to smooth tube was computed for all the devices. Depending on Reynolds number and insert geometry fi/fs values ranged from 1.3 to 79.8. Furthermore, detailed temperature profiles were obtained for different sections along the absorber plate and the risers for five different mass flow rates covering the Reynolds range from [400–2500]. The increase of the inner heat transfer coefficient by the inserts caused an important decrease of the absorber temperature. At increasing mass flow rates (from Re ≈ 1000), all the inserts showed a very similar thermal performance which make them suitable for inserting within harp-type solar collectors, where pressure drop is not a constraint. The best inserts TT03, WC01 and WC02 gave at Re ≈ 1500 maximum absorber temperature decreases (insert vs smooth tube) of 5.05 °C, 5.40 °C and 5.34 °C. In serpentine-type solar collectors, due to pressure drop constraints, the wire coil WC01 with a moderate pitch to wire-diameter ratio (p/d = 1.5 and e/d = 0.07), is the best specimen to insert. WC01 presents a moderate pressure drop increase (fi/fs = 2.8 at Re ≈ 1000), an early promotion of turbulent flow (at Re ≈ 700), and a significant reduction of the absorber temperature (decreasing 4.84 °C vs smooth tube at Re ≈ 1000).

Aerodynamic design methodology for wind tunnel tests of wind turbine rotors

This paper illustrates the methodology and the experimental verification of the design of a 1/75 aero-elastic scaled rotor of the DTU 10 MW reference wind turbine for wind tunnel tests. The aerodynamic design was focused on the minimization of the difference, in terms of thrust coefficient, with respect to the full scale reference. From the Selig low-Reynolds airfoils database, the SD7032 one was chosen for this purpose and a corresponding constant section wing was tested at DTU red wind tunnel, providing force and distributed pressure coefficients for the design, in the Reynolds range 30−250×103 and for different angles of attack. The aero-elastic design algorithm was set to define the optimal spanwise thickness over chord ratio (t/c), the chord length and the twist, in order to match at least the first flapwise scaled natural frequency. An aluminium mould for the carbon fibre autoclave process was CNC manufactured based on B-Splines CAD definition of the external geometry given as an output of the design procedure. Wind tunnel tests at were carried out Politecnico di Milano on the whole 1/75 wind turbine scale model, confirming the successful aerodynamic design and manufacturing approaches. The experimental modal analysis carried out to verify the structural consistency of the scaled blade is also reported.

Trace element mapping by LA-ICP-MS: assessing geochemical mobility in garnet

A persistent problem in the study of garnet geochemistry is that the consideration of major elements alone excludes a wealth of information preserved by trace elements, particularly the rare-earth elements (REEs). This is despite the fact that trace elements are generally less vulnerable to diffusive resetting, and are sensitive to a broader spectrum of geochemical interactions involving the entire mineral assemblage, including the growth and/or dissolution of accessory minerals. We outline a technique for the routine acquisition of high-resolution 2D trace element maps by LA-ICP-MS, and introduce an extension of the software package XMapTools for rapid processing of LA-ICP-MS data to visualise and interpret compositional zoning patterns. These methods form the basis for investigating the mechanisms controlling geochemical mobility in garnet, which are argued to be largely dependent on the interplay between element fractionation, mineral reactions and partitioning, and the length scales of intergranular transport. Samples from the Peaked Hill shear zone, Reynolds Range, central Australia, exhibit contrasting trace element distributions that can be linked to a detailed sequence of growth and dissolution events. Trace element mapping is thus employed to place garnet evolution in a specific paragenetic context and derive absolute age information by integration with existing U–Pb monazite and Sm–Nd garnet geochronology. Ultimately, the remarkable preservation of original growth zoning and its subtle modification by subsequent re-equilibration is used to ‘see through’ multiple superimposed events, thereby revealing a previously obscure petrological and temporal record of metamorphism, metasomatism, and deformation.

Evolution of an eroding cylinder in single and lattice arrangements

The coupled evolution of an eroding cylinder immersed in a fluid within the subcritical Reynolds range is explored with scale resolving simulations. Erosion of the cylinder is driven by fluid shear stress. Kármán vortex shedding features in the wake and these oscillations occur on a significantly smaller time scale compared to the slowly eroding cylinder boundary. Temporal and spatial averaging across the cylinder span allows mean wall statistics such as wall shear to be evaluated; with geometry evolving in 2-D and the flow field simulated in 3-D. The cylinder develops into a rounded triangular body with uniform wall shear stress which is in agreement with existing theory and experiments. We introduce a node shuffle algorithm to reposition nodes around the cylinder boundary with a uniform distribution such that the mesh quality is preserved under high boundary deformation. A cylinder is then modelled within an infinite array of other cylinders by simulating a repeating unit cell and their profile evolution is studied. A similar terminal form is discovered for large cylinder spacings with consistent flow conditions and an intermediate profile was found with a closely packed lattice before reaching the common terminal form.

Influence of Different Arranges of Vortex Generators on Heat Transfer

In this paper, effects of flat plate obstacles and rectangular and triangular decorated bars on cooling of a hot bar were investigated experimentally and numerically. The experiments were performed in a wind tunnel with transient heat transfer through the hot bar. Results showed that in case of staggered tube banks and Reynolds range of 350–2100, heat transfer increased from 10 to 30 % while pressure decreased from 55 to 34 % and in case of in-line tube banks and the same range of Reynolds, heat transfer encountered a rise from 10 to 20 % and the pressure reduced from 15 to 8 %. Moreover our study indicates the Nusselt increased when Reynolds number enhances, furthermore, the Nusselt variation corresponding to the rectangular flat obstacles was compared to other modes.

On the aero-elastic design of the DTU 10MW wind turbine blade for the LIFES50+ wind tunnel scale model

This paper illustrates the aero-elastic optimal design, the realization and the verification of the wind tunnel scale model blades for the DTU 10 MW wind turbine model, within LIFES50+ project. The aerodynamic design was focused on the minimization of the difference, in terms of thrust coefficient, with respect to the full scale reference. From the Selig low Reynolds database airfoils, the SD7032 was chosen for this purpose and a proper constant section wing was tested at DTU red wind tunnel, providing force and distributed pressure coefficients for the design, in the Reynolds range 30-250 E3 and for different angles of attack. The aero-elastic design algorithm was set to define the optimal spanwise thickness over chord ratio (t/c), the chord length and the twist to match the first flapwise scaled natural frequency. An aluminium mould for the carbon fibre was CNC manufactured based on B-Splines CAD definition of the external geometry. Then the wind tunnel tests at Politecnico di Milano confirmed successful design and manufacturing approaches.

JT-60SA TF Coils: Experimental Check of Hydraulic Operating Conditions

The general design of the JT-60SA toroidal field (TF) system relies on the use of a single-channel cable-in-conduit conductor defined in agreement with all participants of the project (CEA, ENEA, F4E). The hydraulic data of a TF conductor reference was used for design assessment. The characterizations of the production conductor, done on relevant unit length and on short samples, have highlighted higher pressure drop than expected. The results have led to estimate a cryoplant operating point much lower than expected and an unequal flow between conductors inside the coils. An extensive characterization program was then engaged on short conductor samples extracted from conductor unit lengths covering almost 75% of the full production. This paper reports about these tests, which were performed on a large Reynolds range. The assessment of the real operating point and the resulting flow distribution inside the coils is presented. These data could be used by experts as input to better understand the coil behavior during cold testing and normal operation at final JA site.

Conventional measuring probes in the wall layer of turbulent subsonic ducted flows

This piece of work is concerned with the application of two conventional measuring probes, pressure probe and hot wire, in the wall layer of subsonic ducted, pipe and channel, flows for velocity measurements. Careful measurements have been carried out and analysed accordingly for Reynolds number range of 2.8×105≤Rem≤4.5×105 and 4×104≤Rem≤2.3×105 for the pipe and the channel, respectively. Pressure probes of outer diameters (d 0 + = d 0·uτ/v) 20-120 wall units and hot wire, having wire length (l+= l uτ/v) of 50-250 for the current Reynolds range, have been utilized to carry out the present measurements. When the pressure probe was applied in the wall layer, the wall proximity and the shear gradient played major roles of its incorrect velocity readings, however, this effect was far from being influencing the hot-wire velocity measured in the overlap region. When the pressure probe results compared to those obtained by the hot wire, the pressure probe's data showed hump in the normalized mean velocity profiles around the wall distances y+≤300 and y+≤150 for the pipe and the channel, respectively. Available corrections are adopted and applied to the pressure probe data measured, yielding results that are comparable to those of the hot wire and this was also demonstrated by comparing the present results corrected to the so-called the logarithmic velocity profile.

Experimental investigation on heat transfer and pressure drop of conical coil heat exchanger

The heat transfer and pressure drop analysis of conical coil heat exchanger with various tube diameters, fluid flow rates, and cone angles is presented in this paper. Fifteen coils of cone angles 180? (horizontal spiral), 135?, 90?, 45?, and 0? (vertical helical) are fabricated and analysed with, same average coil diameter, and tube length, with three different tube diameters. The experimentation is carried out with hot and cold water of flow rate 10 to 100 L per hour (Reynolds range 500 to 5000), and 30 to 90 L per hour, respectively. The temperatures and pressure drop across the heat exchanger are recorded at different mass flow rates of cold and hot fluid. The various parameters: heat transfer coefficient, Nusselt number, effectiveness, and friction factor, are estimated using the temperature, mass flow rate, and pressure drop across the heat exchanger. The analysis indicates that, Nusselt number and friction factor are function of flow rate, tube diameter, cone angle, and curvature ratio. Increase in tube side flow rate increases Nusselt number, whereas it reduces with increase in shell side flow rate. Increase in cone angle and tube diameter, reduces Nusselt number. The effects of cone angle, tube diameter, and fluid flow rates on heat transfer and pressure drop characteristics are detailed in this paper. The empirical correlations are proposed to bring out the physics of the thermal aspects of the conical coil heat exchangers.

Field tests of multiple 1/10 scale tidal turbines in steady flows

Queen's University Belfast and Wave Barrier Ltd have developed a tidal testing platform to test hydrokinetic turbines at medium scale. Multiple turbines can be pushed through still water conditions, in steady-state pushing tests. Experiments were conducted to evaluate the interactions between two identical, mono-strut, horizontal axis tidal turbines (HATTs) of 1.5 m diameter (D) rotor. Their relative performance when located individually, in-plane and in-line are investigated. The data shows a high consistency in the power curves at different flow speeds, which indicates high repeatability in this Reynolds range. For an individual turbine, there is no performance difference when the rotor is mounted either upstream or downstream of the supporting structure. When placed in-plane, the turbines have no adverse effect on one another. When spaced in-line with 2D separation, there is a 63% reduction in the performance of the downstream turbine. At 6D downstream this performance reduction is still 59%, indicating some wake recovery between 2D and 6D, though the influence from the upstream rotor persists to at least 6D downstream of the first device. In contrast the performance of the downstream turbine when placed at 1.5D offset of the upstream device at 6D downstream is approximately recovered to the individual turbine performance.

Resistive thrust production can be as crucial as added mass mechanisms for inertial undulatory swimmers.

In this Rapid Communication, we address a crucial point regarding the description of moderate to high Reynolds numbers aquatic swimmers. For decades, swimming animals have been classified in two different families of propulsive mechanisms based on the Reynolds number: the resistive swimmers, using local friction to produce the necessary thrust force for locomotion at low Reynolds number, and the reactive swimmers, lying in the high Reynolds range, and using added mass acceleration (described by perfect fluid theory). However, inertial swimmers are also systems that dissipate energy, due to their finite size, therefore involving strong resistive contributions, even for high Reynolds numbers. Using a complete model for the hydrodynamic forces, involving both reactive and resistive contributions, we revisit here the physical mechanisms responsible for the thrust production of such swimmers. We show, for instance, that the resistive part of the force balance is as crucial as added mass effects in the modeling of the thrust force, especially for elongated species. The conclusions brought by this work may have significant contributions to the understanding of complex swimming mechanisms, especially for the future design of artificial swimmers.

Genesis of the central zone of the Nolans Bore rare earth element deposit, Northern Territory, Australia

The Nolans Bore rare earth element (REE) deposit consists of a network of fluorapatite-bearing veins and breccias hosted within Proterozoic granulites of the Reynolds Range, Central Australia. Mineralisation is divided into three zones (north, central, and south-east), with the north and south-east zones consisting of massive REE-bearing fluorapatite veins, with minor brecciation and carbonate infill. The central zone is distinctively different in mineralogy and structure; it features extensive brecciation, a high allanite content, and a large, epidote-rich enveloping alteration zone. The central zone is a reworking of the original solid apatite veins that formed during the Chewings Orogeny at ca. 1525 Ma. These original apatite veins are thought to derive from phosphate-rich magmatic–hydrothermal fluid exsolved from as-yet unrecognised alkaline magmatic bodies at depth. We define four ore breccia types (BX1–4) in the central zone on the basis of detailed petrological and geochemical analysis of drillcore and thin sections. BX1 ore comprises fluorapatite with minor crackle brecciation with carbonate infill and resembles ore of the north and south-east zones. Breccia types BX2, BX3, and BX4 represent progressive stages of ore brecciation and development of calc-silicate mineral (amphibole, epidote, allanite, calcite) infill. Comparison of bulk ore sample geochemistry between breccia types indicates that REEs were not mobilised more than a few centimetres during hydrothermal alteration and brecciation. Instead, most of the REEs were partitioned from the original REE fluorapatite into newly formed allanite, REE-poor fluorapatite and minor REE carbonate in the breccias. Negative europium (Eu) anomalies in the breccia minerals are accounted for by a large positive Eu anomaly in epidote from the alteration zones surrounding the ore breccias. This observation provides a direct link between ore recrystallisation and brecciation, and the formation of the alteration halo in the surrounding host rocks. Where allanite and fluorapatite are texturally related, the fluorapatite is relatively depleted in the light rare earth elements (LREEs), whereas allanite is relatively LREE enriched, suggesting co-crystallisation. We tentatively date the BX1 ore stage to 1440 ± 80 Ma based on U–Pb dating of thorianite. Sm–Nd isotope isochrons derived from in situ isotope analysis of cognate apatite and allanite date the BX2 and BX3 events to ca. 400 Ma, while U–Pb dating of late-stage monazite from the BX4 ore stage returned an age of ca. 350 Ma. Therefore, formation of the central zone at Nolans Bore involved multiple alteration/brecciation events that collectively span over 1 billion years in duration. We suggest that the BX1-type veins and breccias were formed from REE-rich, saline (F- and Cl-bearing) fluids that infiltrated the granulite-grade host rocks in association with either shear activation events of the Redbank Shear Zone (1500–1400 Ma) or intrusion of late-stage pegmatites of the Mt Boothby area. BX2, BX3, and BX4 events record deformation and hydrothermal alteration associated with the Alice Springs Orogeny (400–350 Ma). These hydrothermal events occurred at temperatures of 450 to ~600 °C, due to inflow of highly acidic hydrous fluids derived from a magmatic source, or from mixing of meteoric and metamorphic fluids. Our data testify to the long and complex geological history of not only the Nolans Bore REE deposit, but also of the rocks of the eastern Reynolds Range, and demonstrate the great utility of using hydrothermally derived REE minerals to trace the timing of crustal deformation events and source of associated hydrothermal fluids.

The effect of low Reynolds number flows on pitot tube measurements

An investigation on the low Reynolds number effect on hemispherical-tipped Pitot tube measurements was performed by measuring the center-line velocity during the laminar flow of a Newtonian fluid in a 25mm (1in.) diameter vertical recirculating pipe loop. The primary objective of the study was to reconsider the available low Reynolds number Pitot tube data in the literature with modern instrumentation.Using the results of this experimental study, a correlation that accurately predicts the low Reynolds number Pitot tube behavior has been developed. The correlation accounts for an additional viscous term in the relationship for the pressure coefficient (Cp) which is not accounted for in Bernoulli's Equation. The correlation is semi-empirical and accurately fits experimental data gathered in this study, as well as a significant body of experimental data available in the literature. The correlation, which is based on a Pitot tube Reynolds number calculated using the opening diameter (d), has been shown to be provide more accurate predictions of Cp for a wide range of opening diameter to outer diameter ratios (0.22≤d/D≤0.6) than available correlations based on outer diameter.The transition Pitot tube Reynolds number, below which Bernoulli's Equation is no longer appropriate, was predicted to be approximately 35, compared to a value of 79 obtained from fitting data collected by Barker. The correlation developed in this study provides smoother transitions at both ends of the low Reynolds range. At the low end (Re<10) it converges with a Stokes Law’ analogy, while at the critical transition (Re~35) it converges asymptotically with Bernoulli's Equation. The correlation also accurately predicts the behavior of the pressure coefficient with Reynolds numbers between these ranges.

LA-ICP-MS U–Pb dating of detrital rutile and zircon from the Reynolds Range: A window into the Palaeoproterozoic tectonosedimentary evolution of the North Australian Craton

The Palaeoproterozoic Reynolds Range of the Arunta Region, central Australia, comprises a series of shallow marine clastic sediments (Reynolds Range Group) which overlies deeper water sequences of turbidites (Lander Rock Formation) and minor sandstones (“unnamed sandstone”). U–Pb age data collected from detrital rutile and zircon in these rocks indicates these sequences contain very similar age spectra, although with a notable and important shift to younger ages within the stratigraphically younger Reynolds Range Group. Detrital zircons from the “unnamed sandstone” directly underlying the unconformity with the Reynolds Range Group contain a major age component at ca. 1860Ma, together with a wide spread of ages between ca. 3.2 and 2.0Ga and a minor age component of 1830–1805Ma. Detrital rutile from the same rock yield a unimodal age spectrum with a mean age of ca. 1840Ma. The detrital zircon age spectrum from the Reynolds Range Group is similar, although the youngest cluster of ages is younger and dates to between 1800Ma and 1780Ma. Detrital rutile from these rocks yield a unimodal age spectrum with a mean age of ca. 1790Ma. Although the observed differences in ages are subtle, we suggest these nevertheless mark a significant change in provenance.We attribute the predominance of 1860–1820Ma detrital zircon and 1840Ma detrital rutile within the “unnamed sandstone” and the characteristic ca. 1860Ma detrital zircon age cluster in previously published provenance studies from the Lander Rock Formation to uplift and erosion of the Halls Creek–Pine Creek Orogen. This orogenic belt marks collision between the North Australian and Kimberley cratons, an event dated to between 1835Ma and 1810Ma and which incorporates marginally older rocks dating to 1860Ma from the foreland of the Kimberley Craton. By contrast we attribute the influx of younger rutile and zircon, together with a distinct facies change observed with the onset of the deposition of the Reynolds Range Group, to a shift in provenance region to the Yapungku Orogen, which marks the collision between the West Australian and North Australian cratons and is dated to ca. 1800–1765Ma. A change in provenance is additionally consistent with significant differences in rutile trace element composition.The Lander Rock Formation and the Reynolds Range Group are stratigraphically correlated with sedimentary rocks that overly large parts of the North Australian Craton. We suggest this indicates spatially continuous basinal conditions within the North Australian Craton between ca. 1840Ma and 1780Ma, although the erosion and drainage systems feeding this basin were strongly influenced by the collision and orogenesis along the northwest and southwest margins of the North Australian Craton.

Thermal Performance of a Water-Cooled Microchannel Heat Sink With Grooves and Obstacles

With the rapid development of microelectromechanical systems (MEMS) in IT industry, the heat flux in microchannel has reached a high level which demands preferable cooling technology. Water cooling has become a favor cooling approach in electronic microdevices due to better thermal performance than air cooling method. In the present paper, thermal performance in microchannels with grooves and obstacles are investigated numerically. The height and width of the rectangular microchannel are 200 and 50 μm, respectively. As a simple modification of dimple/protrusion, the groove/obstacle diameter is 100 μm and the depth is 20 μm. Different arrangements of grooves and obstacles are considered on Reynolds range of 100–900. The numerical results show that groove/obstacle structure is effective for cooling enhancement in microchannel. Among the cases in this research, the normalized Nusselt number Nu/Nu0 is within the range of 1.446–26.19, while the pressure penalty f/f0 has a much larger range from 0.86 to 110.18 depending on specific orientation. Field synergy analysis and performance evaluation plot are adopted to discuss the mechanism of heat transfer enhancement and energy saving performance integrating the pumping performance. From the viewpoint of energy saving, groove on single surface (case 1) has the best performance. Furthermore, performances of grooved microchannels are compared with that of dimpled microchannels which were discussed in the author’s previous research. The results indicate grooved microchannels have larger range of both Nu/Nu0 and f/f0 and some grooved cases possess high TP than dimpled microchannels.

Modeling of a microreactor for propylene production by the catalytic dehydrogenation of propane

A model of a microreactor was proposed to analyze the production of propylene by the propane dehydrogenation using a catalytic surface of V2O5/TiO2 doped with Rb. The reactor is a 50mm length tube of 2mm diameter whose wall is a catalytic surface, modeled using finite volume method in cylindrical coordinates over a tangential plane. Dehydrogenation kinetics is reported by Grabowski (2004). First, a mesh independence analysis was done to assure the adequate cell size. Second, a parametric analysis changing Reynolds number at different temperatures and propane-oxygen relations was done to find the Reynolds range to effectively use the reactor length (Re from 1 to 10). Then at the later Reynolds interval a parametric analysis involving temperature and composition was done to create productivity surfaces to find the highest productivity operation conditions. Finally, an analysis varying pressure at the maximum productivity conditions (Re=1, T=500K, C3H8/O2=2) was developed.

Development of a gas phase combustion model suitable for low and high turbulence conditions

A novel hybrid gas phase combustion model suitable for low as well as high turbulent combustion conditions is proposed. In particular, in the region above the fuel bed of small-scale biomass combustion plants, gas phase mixing is highly influenced by laminar and low turbulence zones. Here, the eddy break-up combustion models are not valid because they were originally developed for highly turbulent flows. Therefore, a CFD gas phase reaction model applicable over the whole Reynolds range from laminar to turbulent flows is developed. It is a hybrid Eddy Dissipation Concept/finite rate kinetics model which calculates the effective reaction rate from laminar finite rate kinetics and the turbulent reaction rate and weights them depending on the local turbulent Reynolds number of the flow. To validate the proposed model, comparisons are made with experimental data for a series of jet flames covering laminar, transitional, and turbulent flow conditions. The simulation results show that the prediction of flame can be improved with the proposed hybrid combustion model.

Turbulent drag reduction at moderate Reynolds numbers via spanwise velocity waves

AbstractThe question whether large turbulent drag reduction can be achieved at the high values of Re typical of applications is addressed. Answering such question, either by experiments or DNS, is obviously challenging. For DNS, the problem lies in the tremendous increase of the computational cost with Re, that has to be appreciated in view of the need of carrying out an entire parametric study at every Re, owing to the unknown location of the optimal forcing parameters.In this paper we limit ourselves to considering an open‐loop technique based on spanwise forcing, the streamwise‐traveling waves introduced by [1], and explore via Direct Numerical Simulations (DNS) how the drag reduction varies when the friction Reynolds number is increased from Reτ = 200 to Reτ = 2000. To achieve high Re while keeping the computational cost affordable, computational domains of reduced size are employed. We adopted special care to interpret results that are indeed still box‐size dependent, as well as strategies to compute the random errors and give the results an error bar.Our results indicate that still R = 0.29 can be obtained at Reτ = 2000 in the partial region of the parameter space studied. The maximum R is found to decrease as R ˜ Reτ−0.22 in the Reynolds range investigated. As most important outcome, we find that the sensitivity of R to Re becomes smaller when far from the low‐Re optimum parameters: in this region, we suggest R ˜ Reτ−0.08. (© 2012 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)