Turbulent Kinetic Energy Contours Research Articles

Pressure distribution effects due to chevron fences on film cooling effectiveness and flow structures

In the present study, film cooling effectiveness behavior for novel fence geometries were investigated depending on flow structures and related pressure patterns. Eleven fence geometries are evaluated. Generally, it can be described as upstream chevrons with sharp and rounded edges instead of straight shapes. The film cooling effectiveness was investigated and compared with experiments with and without fences, which are available in literature review. Velocity profiles, static pressure coefficient profiles and turbulence kinetic energy contours were discussed. Blowing ratios in the range of 0.5, 1, 1.5 and 2 were investigated. Results show that the fence cases are characterized by three pressure coefficient peaks that are responsible for generating useful higher pressure difference between the leading edge of a film hole and the midline region to improve coolant lateral spreading. Results indicate that the best novel fence is chevron with rounded edge “case (e)” with higher film cooling effectiveness levels compared with the experiments.

Comparison of turbulent flow through hexagram and hexagon orifices in circular pipes using large-eddy simulation

Characteristics of turbulent flow through a circular, a hexagon and a hexagram orifice with the same flow area in circular pipes are investigated using wall-modelled large-eddy simulation. Good agreements to available experimental data were obtained in both the mean velocity and turbulent kinetic energy. The hexagram orifice with alternating convex and concave corners introduces outwards radial velocity around the concave corners downstream of the orifice plate stronger than the hexagon orifice. The stronger outwards radial velocity transfers high momentum from the pipe centre towards the pipe wall to energize the orifice-forced vortex sheet rolling-up and leads to a delayed vortex break-down. Correspondingly, the hexagram has a more gradual flow recovery to a pipe flow and a reduced pressure drop than the hexagon orifice. Both the hexagon and hexagram orifices show an axis-switching phenomenon, which is observed from both the streamwise velocity and turbulent kinetic energy contours. To the best knowledge of the authors, this is the first comparison of orifice-forced turbulence development, mixing and flow dynamics between a regular and a fractal-based polygonal orifice.

CFD Simulations of Film Cooling Effectiveness and Heat Transfer for Annular Film Hole

The increasing turbine entry temperature has placed demands for improvements in engine cooling, and the work described in this paper is the development of a new film cooling configuration to meet this demand. In this study, numerical simulations were performed to predict the improvement in film cooling performance with novel film hole called an annular film hole. The film cooling performance parameters such as heat transfer coefficient (h), film cooling effectiveness (\({\eta)}\) and the net heat flux reduction (NHFR) over flat plate were investigated and compared with other configurations. Velocity profiles, pressure coefficient and turbulence kinetic energy contours were discussed. Four mass flow rates of secondary flow fluid were used to investigate the effects of film coolant velocity on the film cooling performance behavior. Results indicate that an annular film hole gives high film effectiveness, low heat transfer coefficient and higher NHFR compared to rectangular and circular film holes. The average values of laterally averaged film cooling effectiveness of the annular film hole increased to 106 and 328.5% compared with the rectangular and circular film holes at moderate flow rate, respectively. This difference is attributable to decreasing the jet vertical velocity component in a case of the annular hole. Also the low and high heat transfer coefficient regions were described for annular hole in detail.

Numerical study of flow field in new cyclone separators

Numerical study of the fluid flow and particle dynamics is presented by numerical techniques to characterize the performance of new cyclone separators. The design of this cyclone is based on the idea of improving cyclone performance by increasing the vortex length. This cyclone differs from a conventional cyclone with the separation space. Instead of conical part, the separation space of this cyclone consists of an outer cylinder and a vortex limiter. The Reynolds averaged Navier–Stokes equations with Reynolds stress turbulence model (RSM) are solved by use of the finite volume method based on the SIMPLE pressure correction algorithm in the computational domain. The Eulerian–Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW). In the results the dependency of collection efficiency and pressure drop on different geometrical parameters is investigated. Contours of velocity, pressure and turbulent kinetic energy within these cyclones are shown. Tangential velocity profiles and velocity vectors in different sections are investigated.

Film cooling effectiveness and flow structures for novel upstream steps

In this study, computational simulations were made using ANSYS CFX to predict the improvements in film cooling performance by using novel upstream steps. There are twenty-one novel steps consisting of three groups are tested. The first group consists of a rectangular step with different tilt angles. The second group consists of a normal rectangular step with and without segmentation. The third group consists of curved steps with and without segmentation. Optimizing the curved steps dimensions is performed. The film cooling effectiveness (η) of twenty-one novel steps were investigated and compared with experiment. Velocity profiles, pressure coefficient profiles and turbulent kinetic energy contours were discussed. Blowing ratios in the range (0.5, 1, 1.5 and 2) were investigated. Results indicate that the best novel step is the curved step with width (W/8) and the average values of film cooling effectiveness is increased to 138.8% compared with the experiment.

Effect of Baffles on the Sloshing in Road Tankers Carrying LPG: A Comparative Numerical Study

This work presents a comparative numerical study of the effect of using baffles, and its design, on the behavior of sloshing in a partially filled road tanker carrying LPG. Navier-Stokes equations and standardk-εturbulence model are used to simulate fluid movement; the Volume of Fluid (VOF) method is used to track the liquid-gas interface. Velocity distributions, sloshing stabilization times, and contours of turbulent kinetic energy, which are of high importance in choosing the best design of baffles, are shown. The results show sloshing stabilization times of 22 and 21 s for road tankers with cross-shaped (Type I) and X-shaped (Type II) baffles, respectively, finding lower values of turbulent kinetic energy for Type II design, being, therefore, the best design of baffles for damping of sloshing and vehicle control among studied ones.

Prediction of HCCI Engine Performance with Three Zone Extended Coherent Flame Combustion Model

Soot, NOx paradox in compression ignition engines is an extremely challenging issue. Low temperature combustion followed by Homogeneous charge compression ignition (HCCI) type of combustion is capable of reducing nitrogen oxides and soot simultaneously. Homogeneous charge compression ignition (HCCI) has a potential for high fuel conversion efficiency and extremely low emissions of particulate matter and oxides of nitrogen (NOx). However, feasibility of HCCI is also posing certain issues .In this paper, three zone extended coherent flame combustion model of STAR-CD package has been used to study the CI engine in both conventional and HCCI mode. A comparison of important parameters like in-cylinder pressure, temperatures, CO, NOx emissions, in conventional and HCCI mode are predicted. Relatively Low in-cylinder pressures and temperatures are realized in HCCI mode when compared to conventional mode of combustion. Uniform mixing of fuel-air, turbulent kinetic energy and velocity contours are obtained in HCCI mode. Key Words: HCCI, ECFM-3Z, Phi-T charts, Piston Work, Turbulent Kinetic energy.

Control of the Separation Flow in a Sudden Enlargement

In the present paper, an experimental and numerical investigation of fluid flow and heat transfer in the case of wall injection besides main flow through a circular sudden enlargement are studied. The injected flow is achieved through an annular slot placed around the inner side wall of the step. The static pressure variation along the sudden enlargement length is measured and calculated at different values of injection ratio ( Q ) and injection flow angles. The average heat transfer with Reynolds number (ReJ) of injected flow at different values of the inlet flow angle is obtained. The velocity, turbulent kinetic energy and temperature contours are presented in this study. Reynolds number of injected flow is varied between 320 and 840, Reynolds number of main flow is between 5895 and 8450 and the injection flow angles are 0 o , 15 o , 30 o , 45 o and 60 o . In the injection case, the results indicate that, the pressure recovery coefficient increases by decreasing the injection ratio and increasing the flow angle. The average heat transfer coefficient increases as both injection Reynolds number and the injection flow angle increase. The numerical results showed that two recirculation zones generate behind the step between the injection flow and the main flow. The size of these recirculation zones decreases by increasing the injection flow rate. The turbulent kinetic energy increases within region between the recirculation zones and main zone also, it decays by injecting flow in the recirculation zone. The length for higher value of flow temperature decreases by injecting flow in the recirculation zone, and that length increases as the injection flow rate increases. The comparison between the experimental results and the numerical results gives good agreement using the k-e model with Leschziner and Rodi correction.

Effect of submergence depth of the ladle shroud on liquid steel quality output from a delta shaped four strand tundish

Physical and mathematical modelling was performed in a full-scale water model tundish to study the effect of the submergence depth of the shroud on melt flow and liquid metal quality. In the full-scale water model tundish, slag entrainment tests were performed at various immersion depths of the shroud. Polyethylene beads (920 kg m−3) were used to simulate the slag phase and the number of beads collected in each submerged entry nozzle during a ladle change, indicated relative performances in terms of slag entrainment. A three-dimensional mathematical model was developed and contours of turbulence (turbulent kinetic energy (TKE) contours) were examined at different depths of submergence of the ladle shroud. At low depths of submergence there is high turbulence within the tundish and this causes more slag entrainment. On the contrary, at high submergence depths there is very low turbulence and hence amount of slag entrained is less. Tundish operations with higher submergence depth of the shroud may eliminate the use of turbulence inhibitors and thereby reduce refractory consumption and cost.

곡관부 하류에 핀휜이 부착된 회전 냉각유로의 최적설계

This study investigates a design optimization of a rotating two-pass rectangular cooling channel with staggered arrays of pin-fins. The radial basis neural network method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The ratio of the diameter to height of the pin-fins and the ratio of the streamwise spacing between the pin-fins to height of the pin-fin are selected as design variables. The optimization problem has been defined as a minimization of the objective function, which is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. Results are presented for streamlines, velocity vector fields, and contours of Nusselt numbers, friction coefficients, and turbulent kinetic energy. These results show how fluid flow in a two-pass square cooling channel evolves a converted secondary flows due to Coriolis force, staggered arrays of pin-fins, and a turn region. These results describe how the fluid flow affects surface heat transfer. The Coriolis force induces heat transfer discrepancy between leading and trailing surfaces, having higher Nusselt number on the leading surface in the second pass while having lower Nusselt number on the trailing surface. Dean vortices generated in turn region augment heat transfer in the turning region and in the upstream region of the second pass. As the result of optimization, in comparison with the reference geometry, thermal performance of the optimum geometry shows the improvement by 30.5%. Through the optimization, the diameter of pin-fin increased by 14.9% and the streamwise distance between pin-fins increased by 32.1%. And, the value of objective function decreased by 18.1%.

Numerical investigation of fluid flow and heat transfer characteristics by common-flow-up

Effects of the common-flow-up pair produced by vortex generators in a rectangular channel flow on fluid flow and heat transfer are numerically investigated. In order to analyze the common-flow-up pair, the pseudo-compressibility method is introduced into the Reynolds-averaged Navier–Strokes equations for a three-dimensional incompressible viscous flow. A two-layer k– ε turbulence model is applied to a three-dimensional turbulence boundary over a flat plate to predict the flow structure and heat transfer characteristics of the common-flow-up pair and to resolve the near-wall flow. Results reasonably predict the flow structure of the common-flow-up pair, such as secondary velocity vectors and turbulent kinetic energy contours. Also, in the prediction of thermal boundary layers, skin friction characteristics and heat transfer characteristics, the present results are reasonably close to the experimental results of other researchers even though some discrepancies are observed near the center of the vortex core.

The flow across a street canyon of variable width—Part 1: Kinematic description

Measurements have been made of the scalar dispersion of smoke released from a two-dimensional slot in the wall perpendicular to a boundary layer flow and located parallel to and midway between two square obstacles placed on the wall. The Reynolds number of the boundary layer at the slot location without the obstacles in place is R θ ≈ 980 . Two optical systems with CCD cameras facing each other have been used to measure simultaneously the velocity and scalar concentration fields, respectively, with PIV and Mie scattering diffusion. In Part B of this paper the data will ultimately provide detailed information about the scalar fluxes for this environmentally relevant geometry. Here in Part A the results of the velocity field measurements in the streamwise plane will be reported for spacings between the obstacles of 1–10 obstacle heights. The mean flow measurements reveal the increasing complexity of the canyon flow with increasing obstacle spacing. A primary vortex, with negative spanwise vorticity, occurs within the canyon for all spacings and is driven by the flow above. The circulation region of this vortex extends above the level of the tops of the obstacles. For spacings of 2 h and greater, a secondary vortex with positive vorticity appears in the upstream corner of the canyon, and a tertiary vortex with negative spanwise vorticity first appears in the downstream corner of the canyon for an opening of 6 h . The spatial distribution of the level of turbulence within and around the canyon is indicated by the contours of two-dimensional turbulent kinetic energy, 1 2 ( u 2 ¯ + v 2 ¯ ) . The region of elevated turbulence in the shear layer created by the upstream obstacle penetrates deeper into the canyon with increasing canyon opening. For all openings, the Reynolds shear stress is negative above the canyon. The vertical extent of the high negative stress region increases as the canyon opening increases, and it also penetrates well within the canyon. This region of negative stress is due to the transport, by the primary canyon vortex, of low momentum fluid from deep within the canyon upward and high momentum fluid from above the canyon downward.

Numerical investigation of vortex-induced vibrations for flow past a circular cylinder

The objective of the present investigation is to study the vortex-induced vibrations (VIV) for flow past a circular cylinder. The turbulent flow is simulated by using a 2-D standardk-ɛ model incorporating the finite volume method (FVM) and the Semi-Implicit Method for the Pressure Linked Equations (SIMPLE) algorithm on non-orthogonal boundary-fitted collocated grids. The wall boundaries are approximated with wall functions. In the numerical cases, the turbulent wake patterns are studied by plotting the streamlines and the turbulent kinetic energy contours. The pressure distributions are investigated. Analyses of the vortex-induced force coefficients and the structural vibrations are carried out. The variations of the Strouhal number with the Reynolds number and of the vortex-induced force coefficients with the reduced velocity are obtained. The results show that this numerical approach is feasible and efficient in investigating the VIV problem for a circular cylinder.

Convective mass transport in cross-corrugated membrane exchangers

Cross-corrugated triangular ducts provide high mass transfer capabilities in membrane related gas separations. The mixing effect would intensify the convective mass transfer coefficients on membrane surfaces. By modeling transport of water vapor in dry air, in this study, periodic fully developed fluid flow and mass transfer in a cross-corrugated triangular duct is numerically studied. To model the transitional flow in the topology, a validated low Reynolds number k– ω (LKW) turbulence model is employed to account for the turbulence in the flow. The vapor mass fractions, velocity, and turbulent kinetic energy and specific dissipation rate contours are obtained in the three-dimensional complex domain. The friction factors and the segment mean Sherwood numbers are calculated and correlated with Reynolds numbers, for uniform mass fraction boundary conditions. It is found that the transitional flow is represented by a turbulence center, which intensifies and migrates from the upper wall corrugation to the lower wall corrugation with increasing Reynolds numbers.

Effect of Entrance Shape on Erosion in the Throat of Chokes

Erosion is a complex phenomenon that depends on many factors such as fluid properties, solid particle properties, flow stream velocity, flow geometry, and type of metal. Flow modeling and particle tracking are important tools for predicting erosion. In erosion modeling, it is important to account not only for the factors that influence erosion, but also for changes in some of these factors that occur as the erosion process continues. For example, the change in the geometry resulting can have a significant impact on the erosion results. Geometry changes result when corners, found in couplings and chokes, are eroded with time. This change in geometry due to erosion can drastically change the flow field, especially the turbulent kinetic energy and dissipation rate. Recognizing this change is imperative, since the prediction of particle behavior is heavily dependent on the turbulent kinetic energy. Furthermore, more particle impingements occur in regions with higher turbulent kinetic energy. This paper shows that neglecting the change in the flow field solution resulting from the change in geometry can cause erroneous erosion predictions. A computational study was performed on a choke geometry to demonstrate the importance of incorporating the change in geometry resulting from erosion. Predicted turbulent kinetic energy contours are presented as a function of the changing choke geometry. The predicted erosion rates along the choke are also examined for the various scenarios, and these results are compared to experimental results. Additionally, experimental results obtained from laser doppler velocimeter (LDV) measurements also demonstrate the change in fluctuating velocity (turbulent kinetic energy) as a result of rounding of the entrance of the choke. Results from this study show that it is necessary to update the flow geometry and flow model based on the changing geometry due to erosion. [S0195-0738(00)01004-9]

Detailed Flow Measurements in a Centrifugal Compressor Vaneless Diffuser

Hot-wire anemometer measurements have been made in the vaneless diffuser of a 1-m-dia low-speed backswept centrifugal compressor using a phase lock loop technique. Radial, tangential, and axial velocity measurements have been made on eight measurement planes through the diffuser. The flow field at the diffuser entry clearly shows the impeller jet-wake flow pattern and the blade wakes. The passage wake is located on the shroud side of the diffuser and mixes out slowly as the flow moves through the diffuser. The blade wakes, on the other hand, distort and mix out rapidly in the diffuser. Contours of turbulent kinetic energy are also presented on each of the measurement stations, from which the regions of turbulent mixing can be deduced.

Aerodynamic flow investigations in an isothermal model of an afterburner

Experimental and numerical investigations of the three-dimensional flowfields in an isothermal model of an afterburner are presented. Five-hole pilot probe measurements along the entire length of the model in three different azimuthal planes, allow the determination of three mean velocity components which provide comprehensive information to aid understanding of such complex flows. The numerical calculations are performed using a SIMPLE based algorithm with staggered grid arrangement. The standardk-ɛ model is used for physical modeling. The numerical results agree quite satisfactorily with the time-mean velocity measurements. The predicted turbulence kinetic energy contours have also been presented.

Turbulent Flows in a Model SDR Combustor

An experimental study is reported on the isothermal flow fields in a model solid-propellant ducted rocket combustor with two opposing side inlets. The measurements were made by using a four-beam two-color laser-Doppler velocimeter (LDV). Three values of momentum ratio (Ma/Ms) of the axial- to side-inlet jet—0.025, 0.11, and 1.28—were selected to investigate their effects on the flow characteristics. The Reynolds number, based on the air density, combustor height, and bulk velocity, was 4.56 × 104. The flow field was characterized in terms of the mean-velocity vectors and contours, joint probability functions, mean reattachment lengths, spreading rate of the axial-jet width, and Reynolds stress and turbulence kinetic energy contours. The LDV measured mean reattachment lengths were found to well agree with the corresponding flow-visualization photograph. In addition, the three Ma/Ms values provided three characteristic flows which are useful in testing the computational models. Further, correlations between the present cold-flow and previous reading-flow studies were documented in detail. It was found that from the fluid dynamic point of view Ma/Ms = 0.11 was preferable to the other two values of Ma/Ms.

Experimental investigation of flow about a strut-endwall configuration

An experimental study was conducted to investigate incompressible flow about a strut-endwall configuration positioned within a constant area duct. The endwal boundary layer was tripped, but natural transition occurred on the strut surface. The results indicate that spanwise varying transition on this surface leads to the formation of a secondary vortex which coexists with the horseshoe vortex generated by endwall flow separation upstream of the strut leading edge. Both vortices are similar in strength downstream of the strut trailing edge, and both distort the primary flow and local turbulence structure in the wake-endwall region. The level of distortion is demonstrated by means of axial mean velocity contours, turbulence kinetic energy contours, and Reynolds shear stress contours measured in the cross plane at two streamwise locations. Analysis of the results shows that conventional eddy viscosity and k-epsilon transport equation models are not wholly adequate for predicting this flow situation.

Measurements of mean velocity and turbulent intensities in a free isothermal swirling jet

The objectives of the present measurements are to provide data against which results of numerical prediction procedures can be compared, and quantitative information on the behavior of all turbulent stresses and their correlation to spatial distribution of mean velocity gradients, with a view to improving current understanding of relevant transport processes and to guiding turbulence modeling and prediction efforts of such flows. A laser velocimeter, operating in a constant time interval sampling mode, was used to obtain the measurements. Measured values are presented for the case of strong swirling velocities (with recirculating region). The location and extent of the recirculation region is established. Contours of turbulent kinetic energy, derived from measured data, locate the high-turbulence intensity zones (i.e., zones of intense mixing). Experimental data indicate a strong dependence of the turbulent stresses on the local strain of the mean flow in most regions of the flow, which suggests that an eddy viscosity type of turbulence model, e.g., the k-epsilon model, rather than a Reynolds stress model could be acceptable for the prediction of such flows. 22 references.