Forced Mixer Research Articles

Deformability of Steel-Fiber Beams with External Tape Reinforcement

In 2013, the Lviv National Agrarian University patented the construction of a steel-fiber concrete beam, additionally reinforced with an external steel ribbon armature with end anchors. This technical solution allows reducing the cost of the structure by reducing the complexity of its manufacture, due to the absence of a reinforcing frame in the structure. The purpose of this work is to develop proposals for a refined calculation method of deflections of steel-fiber concrete beams with tape reinforcement on the basis of our experimental studies. 3 beams with dimensions 1500x150x60 mm were manufactured. Beam B-1, reinforced with steel tape 1500x60x3 mm with end stops, did not contain fiber. Beams BF-2 and BF-3 in addition to the specified reinforcement contained fiber, corresponding the coefficient of fiber reinforcement by volume, ρfν = 1,5% i 2% respectively. Compressed prisms of 400x100x100 mm and stretched samples of 700x100x60 mm were also tested to determine the mechanical characteristics of concrete and steel-fiber concrete. Loose beams with a working run of 1400 mm were tested with concentrated force applied along the middle of the length. Mass production fiber produced both in Ukraine and abroad with bent ends HE 1050 1 mm in diameter and 50 mm in length was used for reinforcement. The percentage of fiber reinforcement by volume of concrete beams was taken ρfν = 1.5% and 2% to provide enough bearing capacity of the inclined sections. The cement of grade 400 (activity 42.3 MPa) of the Ivano-Frankivsk plant was used to obtain C20 /25 concrete. The test samples were made of fine-grained concrete containing sand from the Yasinets quarry with a fineness modulus of not more than 2.5. Mixtures for beams were made in a forced mixer. The composition of the mixture was chosen so that the settling of the cone did not exceed 4-6 cm and that the fiber did not settle to the bottom of the form. The composition of the mixture per 1 m3 of the mixture was as follows: cement - 549 kg, sand - 1647 kg, water - 285,5 l. The deflections of the steel-concrete beams were smaller than the steel-concrete beams at equal moments. For example, at the moment of 210 kN·cm the experimental deflection values of beams B-1, BF-2 and BF-3 were equal to 0.116; 0.081 and 0.064 cm, and at the moment 420 kN·cm - 0.380; 0.213 and 0.140 cm, respectively. In this paper, it is proposed to determine deflections using the Mora integral and taking into account the results of the calculation of beams by deformation method. The ratio of theoretical and experimental values of deflections was equal to 0.93 … 1.14.

Influence of mineral nano-fibers on the physical properties of road cement concrete material

In this paper, brucite nano-fiber is processed and used as reinforcement to improve the toughness of road cement concrete material. The brucite nano-fiber is obtained by soaking the natural low-coat brucite short fibers in the superplasticizer solution and then agitating in a forced mixer to refine it to the nano meter level. The mechanical properties as elastic modulus, dry shrinkage, anti-frost, thermal expansion, and flexural fatigue performance of the nano-fiber concrete are investigated. The nano-fiber reinforced cement concrete was also put into practice in highway. Results show that nano-fiber concrete has better toughness. Its flexural strength is 7.4% and 17.7% higher than that of the ordinary fiber concrete and the plain concrete, respectively. Its ratio of compression to flexural strengths is 6.4% and 16.1% lower than that of the rest two. Nano-fiber concrete has lower static modulus and higher dynamic modulus. Compared with ordinary fiber concrete and plain concrete, nano-fiber concrete is 41.0% and 61.3% lower in flexural elastic modulus, and is 1.12 and 1.24 times higher in dynamic modulus of elasticity. Nano-fiber concrete has stronger capability to resist dry shrinkage, freeze-thaw damage, thermal expansion and bending fatigue stresses. Compared with ordinary fiber concrete and plain concrete, nano-fiber concrete is 35.7% and 55.9% lower in dry linear shrinkage; 3.2% and 7.9% less loss rate in compression strength, and 1.9% and 4.5% less loss rate in flexural strength after 50 cycles freezing-thawing; 13.9% and 28.7% lower in coefficient of thermal expansion; and 15% and 50% more longer in bending fatigue service life. Nano-fiber concrete is comprehensively superior to ordinary fiber concrete and plain concrete in cost performance. After more than 8 years traffic practice, the nano-fiber concrete test road is still in good condition.

練り混ぜ時間が壁土の強度特性に及ぼす影響

The mixing time of wall clay is decided based on experience and intuition of plasterers. There is no clear description about the mixing time of wall clay. In this study, the load electric power of bi-axial forced mixer is measured to grasp the optimal mixing time of wall clay. The influence of mixing time on the mechanical characteristics of wall clay is examined based on the unconfined compression tests for every mixing time. As a result, the optimal mixing time of wall clay with much clay fraction is estimated to be about 50 minutes in the range of this study.

Investigation of Tank Pressurization and Pressure Control—Part I: Experimental Study

Self-pressurization and pressure control of cryogenic storage tanks have important design consequences for propellant and life support systems currently being planned for long duration space missions. During self-pressurization, the tank's liquid fill level and the heat load from the surroundings can have significant effects on the tank's thermal stratification and pressurization rate. When controlling pressure with a mixing jet, the velocity and temperature of the jet are important design parameters affecting the thermal destratification and pressure reduction time constants. In this work, a small-scale ground-based experiment was performed, as a precursor to a microgravity experiment, to investigate the effects of these variables on the pressurization and pressure control time constants in the tank and to assess the feasibility of using a forced jet mixer for reduced boil-off pressure control. Local pointwise temperature and pressure measurements, together with qualitative contours of the thermal field in the liquid, vapor, and wall region, were made to identify and characterize important self-pressurization and pressure control trends in 1 g.

Numerical investigation of lobe spacing ratio on performance of forced mixer nozzle

AbstractGeometric models of a lobed mixer nozzle with variation of lobe spacing ratios are created and the corresponding flow fields are simulated using a steady Reynolds Averaged Navier–Stokes (RANS) equation with a realizable k‐ϵ turbulence model and standard wall function. According to the numerical simulation results, the spacing ratio has a large influence on the shape of streamwise vortices, but a relatively small effect on the streamwise vorticity field at the lobe exit. Therefore, at the initial part of mixing, a change of spacing ratio has little effect on the thermal mixing efficiency and the total pressure recovery coefficient. In addition, the thermal mixing efficiency increases sharply at the initial part, and near the nozzle exit it approaches some constant. The development of the total pressure recovery coefficient is totally reverse to the thermal mixing efficiency. It falls rapidly at the beginning. Then the rate of descent gradually slows down, and approaches some constant. At the nozzle exit cross‐section, the thermal mixing efficiency ascends and the total pressure recovery efficiency reduces as the spacing ratio increases. Besides, the thrust coefficient has little relationship to the spacing ratio, with a variation smaller than 0.01 when the spacing ratio increases from 4.87 to 0.497. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20363

Numerical investigation of mixing length on performance of lobed forced mixer nozzles

AbstractGeometric models of a lobed mixer nozzle with variation of mixing length are created and corresponding flow fields are simulated using a steady Reynolds Averaged Navier–Stokes (RANS) equation with realizable k–ϵ turbulence model. The numerical simulation results show that the mixing length of the nozzle has a relatively great influence on the development of streamwise vortices and the effective range for streamwise vortices to intensify mixing is about 0.5D distance from the lobe trailing edge. The change of mixing length has little effect on the thermal mixing efficiency. As for the total pressure recovery coefficient, the shorter the mixing length, the sharper the total pressure recovery coefficient curve. On the nozzle exit section, the thermal mixing efficiency increases at first and then slightly declines, and the total pressure recovery efficiency changes little as the mixing length increases. In addition, the thrust coefficient has some small relationship with the mixing length. The thrust coefficient increases in waves as the mixing length increases and the difference between the maximum and the minimum values is slightly less than 1% when the mixing length increases from 0.4D to D. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library wileyonlinelibrary.com/journal/htj. DOI 10.1002/htj.20343

Numerical investigation of flow mixture enhancement and infrared radiation shield by lobed forced mixer

For the exhaust system of turbo-fan engine, the numerical calculation is used to investigate the different mixer configurations. The method using forward–backward ray-tracing and narrow-band model to predict the radiation from engine exhaust has been developed. The scheme has been validated in accuracy for spectral radiation intensity predictions, and some useful results of practical importance have been obtained to establish its ability for infrared signature analysis of exhaust system. A series of computations on exhaust system model have been conducted to obtain the effects of mixer configuration on the aerodynamic performances and infrared radiation intensity. The results indicate that the lobed forced mixer can increase the mixing efficiency by 65%, decrease the thrust coefficient by 3% only, but the infrared radiation of plum can reduce about 40% relative to confluent mixer at zero degree aspect (normal to nozzle outlet), especially. That means the lobed forced mixer has the remarkable ability to shelter the infrared radiation from the inside enclosure of nozzle.

Kelvin - Helmholtz and Streamwise Vortices in the Near Wake of a Single-Lobe Forced Mixer

In the present experimental investigation, the characteristics of two types of vortices, namely the normal Kelvin-Helmholtz (K-H) and streamwise vortices, generated in the near wake of a lobed forced mixer were examined and evaluated at two velocity ratios (r = U1: U2 = 1:1 and 0.4:1). The lobed forced mixer has only one lobe and was designed to eliminate any possible interactions between the neighbouring vortices generated by the adjacent lobes. Hot-wire anemometer was used to study the K-H vortices via the spectrum analysis. Laser-Doppler anemometer was employed to examine the streamwise vortices. It was found that there were two main frequencies for the K-H vortex in the wake of the forced mixer ( fLM_C and fLM_L); both were higher than the case of plane-free shear layer ( fFP), i.e., fLM_C fLM_L fFP. where fLM_C represents the K-H vortex shedding frequency in the behind the semi-circle part of the trailing edge, whereas fLM_L represents the frequency in the near wake behind the parallel side-walls of the trailing edge. The velocity ratio appeared to have more important effects at point C than at point L. The Strouhal numbers ( StLM_C and StLM_L) reached constant values at the Reynolds number greater than 5 × 105. The K-H vorticities for the velocity ratio r= 0.4 was ∼30 and 110 per cent stronger than for case r= 1 for points L and C, respectively. The K-H vortices were also found to be more contributive to the production of the turbulent kinetic energy in the near wake of the single-lobe forced mixer than the streamwise vortices. The streamwise vortices at r= 0.4 accelerated the breakdown of the K-H vortices, which happened at about one wavelength earlier than r= 1. Finally, the effects of geometry parameters, including lobe height (or penetration angle) and wavelength, were examined.

Semi-Empirical Noise Models for Forced Mixer Jet Noise Predictions

In recent years there has been a significant interest in the development of jet noise prediction models due to increased restrictions on aircraft noise near airports. However, currently there are no industry tools that can be used to predict the noise from the complex flows of modern jet engines that include internal forced mixers. The four-source method is a noise prediction tool applicable to simple coplanar, coaxial jets. In this study the fundamental components of the four-source model are used as the building blocks for a noise prediction method which would be applicable to coaxial jets with internal forced mixers. First, the four-source model is applied to an internally mixed jet with a confluent or axisymmetric mixer. Then, a two-source noise model is proposed to predict the noise for cases with an internal forced mixer. Three variable parameters in this two-source model are optimized to match the forced mixer experimental noise data. It is shown that the two-source noise model is capable of accurately modeling the noise spectra of internally mixed jets with forced mixers.

Grid generation and numerical analysis of multi-stream flow in the complex channel with a forced mixer lobe

The co-located grid, SIMPLEC and Chen-Kim modified k - e turbulence model are applied to investigate numerically the multi-stream flow and temperature fields in the complex channel with a forced mixer lobe at room temperature and at elevated temperature. The body-fitted coordinate grids are generated respectively in subdomains according to the shapes of the channel by solving Poisson’s equations to compose the whole grid of the domain. The large viscosity, linear and simultaneous under-relaxation factors are used to solve the coupling of fluid and solid. The solid grid is complemented at the upper inlet of the secondary flow to keep the same node number at the inlet and at double-wall sub-domains. The numerical results and experimental data show good agreement at room temperature. It is illustrated that the cooling air ejected into the slot between the double plates decreases the temperature of the wall.

Analysis of wearing-out causes for revolving-blade mixers and their reliability improvement

Abstract In road coverings and structures of transport infrastructure, composite mixes of various compositions are used made with either organic or mineral binding agents. Most often they are made in a discreet revolving-blade forced mixer, and the final product quality is subject to the mixer construction and parameters. The present paper analyzes wear causes of a revolving-blade mixer with the most important of them-sticking of grains between the blade end and the bottom. Forces are defined effecting various-sized grains found between the blade end and the mixer bottom. Mixer quality assessment methodology is presented, based on analysis principles of homogeneity dynamics for mix being made by it. It is demonstrated that construction homogeneity estimates are different for mixers with various wearing-out levels. Wearing- out of mixer elements may be reduced and mixing quality for mix may be improved by choosing the optimum distance between the blade end and the bottom fretting and changing blade metal a...

ANALYSIS OF WEARING-OUT CAUSES FOR REVOLVING-BLADE MIXERS AND THEIR RELIABILITY IMPROVEMENT

In road coverings and structures of transport infrastructure, composite mixes of various compositions are used made with either organic or mineral binding agents. Most often they are made in a discreet revolving-blade forced mixer, and the final product quality is subject to the mixer construction and parameters. The present paper analyzes wear causes of a revolving-blade mixer with the most important of them-sticking of grains between the blade end and the bottom. Forces are defined effecting various-sized grains found between the blade end and the mixer bottom. Mixer quality assessment methodology is presented, based on analysis principles of homogeneity dynamics for mix being made by it. It is demonstrated that construction homogeneity estimates are different for mixers with various wearing-out levels. Wearing- out of mixer elements may be reduced and mixing quality for mix may be improved by choosing the optimum distance between the blade end and the bottom fretting and changing blade metal and dimensions. Elastic centrifugal coupling is recommended to decrease transmission strokes.

Scarfing and Scalloping Effects on Lobed Forced Mixer at Low-Speed Conditions

This paper presents the Ž ndings on two aspects of geometric modiŽ cation to a lobed forced mixer, namely scarŽ ng and scalloping. ScarŽ ng the lobes was achieved by alternately extending and cutting back the lobes at the trailing edge, and scalloping the lobeswas achievedby removinga certain percentage of the straight sidewall area in the penetration region.BothmodiŽ cationswere intended to enhance the strength of streamwise circulationwithout causing any undesirable consequences, such as  ow separation at the lobe troughs. Tests were conducted over a range of low-speed subsonic  ow conditions (maximumMach number of » 0:07) by using a three-hole pressure probe and a laser Doppler anemometer. The results showed that scarŽ ng the lobes would be more beneŽ cial than scalloping the lobes if the same level of enhancement for the streamwise circulation were to be achieved. Furthermore, for lobesat the samepenetrationangleandat the samepercentage of surface area change, streamwise circulation generated at the trailing edge was actually higher ( » 15%) for the scarfed lobes than for the scalloped lobes. However, the associated mixing and boundary-layer losses incurred by the scarfed lobes would be higher than those of the scalloped lobes. Finally, the combined effects of the two modiŽ cations on a lobed mixer, that is, a scarfed and scalloped mixer, however, did not promote any signiŽ cant streamwise-circulation enhancement.

Visualization of flows behind the lobed forced mixers using the smoke-wire technique

Flow visualization studies have been conducted using the smoke-wire technique to examine the flows behind lobed forced mixers of different trailing edge configurations (namely a square wave, semi-circular wave and a triangular wave) at a velocity ratio 1:1 across the lobe. The wake region shed by a lobe is found to be the largest with lobe geometry consisting of straight parallel sidewalls. Streamwise vortices are formed within the first four wavelengths downstream of the trailing edge in the square and semi-circular lobed mixers. These vortices are largely responsible for intense mixing at downstream locations. However, similar observation is not found in the case of triangular lobed mixer. The present visualization tests agree qualitatively with the velocity measurements obtained by authors using a laser-Doppler anemometer.

Confined Coaxial Nozzle Flow with Central Lobed Mixer at Different Velocity Ratios

Measurements of turbulent, confined, coaxial nozzle flows with a central four-lobe forced mixer have been obtained by a two-component fibre-optic laser-Doppler anemometer at a Reynolds number of 5.1 x 104 (based on the baseline circular nozzle diameter, Dj = 30 mm, and bulk mean velocity, Ur> of the two streams at 1.7 m/s). Ratios of the annular mean to the core mean velocity (X) were kept at 0.4, 1.1 and 2.0 respectively. Results showed that the mixing processes were greatly enhanced by the formation and interaction of the normal and streamwise vorticity. In particular, the deformation and the subsequent stretching of the normal vortices shed at the nozzle walls by the streamwise vortices played an crucial role in the mixing processes. The higher speed stream appeared to determine the form of mixing downstream. At X = 2.0 and 1.1, the generation of the streamwise vorticity was found to originate from two sources: the geometry of the lobe and the gap between the lobe nozzle peaks and the inner annular wall. The former was important to enhance the mixing between the two co-flowing streams at both velocity ratios while the latter was more important for X, = 2.0 to the mixing between the annular flow and the surrounding still fluid. At X = 0.4, only the geometry of the lobe shed streamwise vorticity which was confined radially within each lobe as the flow traveled downstream. Mixing between the core and the surrounding fluid was better than that between the two co-flowing streams. For all the cases considered, streamwise vortices were dissipated within dDj from the nozzle exit plane. NOMENCLATURE

Computational studies of lobed forced mixer flows

Full Navier-Stokes Analyses have been conducted for the flows behind the trailing edge of a lobed forced mixer. The governing equations are derived from the time-dependent compressible Navier-Stokes equations and discretized in the finite-difference form. A simple two-layer eddy viscosity model has also been used to account for the turbulence. Computed results are compared with some of the velocity measurements using a laser-Doppler anemometer (Yu and Yip (1997)). In general, good agreement can be obtained in the streamwise mean velocity distribution but the decay of the streamwise circulation is underpredicted. Some suggestions to the discrepancy are proposed.

Assessment of Jet Noise Analysis Codes for Multistream Axisymmetric and Forced Mixer Nozzles

Jet noise effects produced by an axisymmetric multistream exhaust nozzle have been examined using computational and experimental techniques. The current approach for designing low noise exhaust systems uses empirical rules and computational e uid dynamics (CFD) calculations aimed at lowering peak velocities and/or temperatures. Engineers need to be able to predict noise directly and use predictions to support their specie c design goals. The computational approach utilized in this paper applies a state-ofthe-art CFD Navier ‐ Stokes analysis (NASTAR), in conjunction with a computationally based aeroacoustics analysis. The aeroacoustic analysis uses mean e ow properties and turbulent kinetic energy/ dissipation variables as input parameters for the aeroacoustic solver. Predictions have been made and compared to experimental data obtained in NASA Lewis Research Center’ s open-jet facility. More specie cally, comparisons of aerodynamic and acoustic parameters have been made for axisymmetric nozzles to identify the effects of turbulence level, compressibility, geometrical sizing, and forward e ight on measured levels of jet noise. Applicability of this analysis approach to three-dimensional forced mixer cone gurations has also been explored, with a limited degree of success.

Experimental investigation of two-stream mixing flows with streamwise and normal vorticity

This study provides detailed velocity information in the mixing region of two-stream mixing flows with streamwise and normal vorticity for the computational fluid dynamics (CFD) methods validation. Three trailing-edge configurations for the dividing mechanism had been considered; namely, a convoluted plate, a lobed forced mixer, and a scalloped forced mixer. The first two have been examined previously by visualization tests (Manning 1991). A velocity ratio of 0.6 was generated with initial turbulent boundary layers and was nominally two-dimensional (2-D). Velocity measurements were made on fine cross-plane grids across the wake region and at several streamwise locations using a two-component laser-Doppler anemometer (LDA). The streamwise vortex development for the lobe mixer and the scalloped mixer underwent a three-step process by which it was formed, intensified, and quickly dissipated. The shear layer growth rates were rapid for the scalloped mixer and lobed mixer cases from the trailing edge to a point where the streamwise vorticity was almost dissipated. Consequently, the growth rate reduced and became lower than that of the convoluted plate. In the absence of the streamwise vorticity, the growth rate for the convoluted plate relied only on the 2-D roll-up of the normal vorticity.

Measurements of velocities in the near field of a lobed forced mixer trailing edge

Abstract Previous experimental studies have shown that the development of flow behind the trailing edge of a lobed forced mixer is greatly influenced by the formation of large-scale streamwise vortices. The main objective of the present study is to establish quantitatively the presence and role of the streamwise vortices in the mixing layer in the near field of a lobed forced mixer trailing edge. The near field was defined as the region within five wavelengths (of the trailing edge profile) from the trailing edge. A two-stream mixing layer with a velocity ratio of 0.6 was generated with initially turbulent boundary layers and nominally two-dimensional flow. Mean flow and turbulence measurements were made on fine cross-plane grids across the wake region and at several streamwise locations using a two-component laser-doppler anemometer. Production of turbulent kinetic energy existed in most parts of the near field enhancing the overall mixing process. The streamwise vortex development underwent a three-step process by which it was formed, intensified and quickly dissipated towards the end of the near field. The distance between two rows of streamwise vortices of alternate signs within a lobe reduced with downstream distance causing the amalgamation and annihilation of the vortices. Analysing this movement of vortices, based on inviscid vortex dynamics, suggested that the normal vortices shed at the trailing edge had actually provided a squeezing (pinched off) effect to two adjacent rows of streamwise vortices within a lobe, forcing them to interact with each other.

Mixing Characteristics of Forced Mixers with Scalloped Lobes

An experimental investigation has been undertaken to study the mixing characteristics of forced mixers with scalloped lobes using a two-component e ber-optic laser Doppler anemometer at a Reynolds number of 2.27 3 10 4 and at a velocity ratio 1:2 across the lobes. The trailing edge of the mixers, without scalloping, had the shape of a square wave, a semicircular wave, and a triangular wave. Scalloping was achieved by eliminating up to 70% of the sidewall area at the penetration region of each lobe. The aspect ratio of each lobe (lobe height-to-wavelength ratio ) was at unity and the half-angles at the penetration region were 22 and 35 deg for the scalloped and the aggressively scalloped mixers, respectively. The wavelength and lobe height were the same for both types of mixer. The results showed that lobe cone gurations appeared to be more important than the penetration angles for the benee t of scalloping to occur. Strengths of the streamwise circulation near the trailing edge for respective scalloped mixers were higher than the nonscalloping cases, largely because of the formation of two pairs of streamwise vortices at each lobe. The subsequent decay rates with downstream distance were also found to be more rapid, indicating that a faster mixing rate can actually be achieved by the scalloped mixers. Additional production of turbulent kinetic energy appeared at about two to three wavelengths downstream of the trailing edge and then asymptote to lower level in the far-e eld region. Spatial uniformity of the mass e ux at the wake region could be achieved at two wavelengths further downstream of the high turbulent kinetic energy region.