Jeyakumar Suppandipillai, Jayaraman Kandasamy, R. Sivakumar, Mehmet Karaca and Karthik K.
This paper aims to study the influences of hydrogen jet pressure on flow features of a strut-based injector in a scramjet combustor under-reacting cases are numerically…
Abstract
Purpose
This paper aims to study the influences of hydrogen jet pressure on flow features of a strut-based injector in a scramjet combustor under-reacting cases are numerically investigated in this study.
Design/methodology/approach
The numerical analysis is carried out using Reynolds Averaged Navier Stokes (RANS) equations with the Shear Stress Transport k-ω turbulence model in contention to comprehend the flow physics during scramjet combustion. The three major parameters such as the shock wave pattern, wall pressures and static temperature across the combustor are validated with the reported experiments. The results comply with the range, indicating the adopted simulation method can be extended for other investigations as well. The supersonic flow characteristics are determined based on the flow properties, combustion efficiency and total pressure loss.
Findings
The results revealed that the augmentation of hydrogen jet pressure via variation in flame features increases the static pressure in the vicinity of the strut and destabilize the normal shock wave position. Indeed, the pressure of the mainstream flow drives the shock wave toward the upstream direction. The study perceived that once the hydrogen jet pressure is reached 4 bar, the incoming flow attains a subsonic state due to the movement of normal shock wave ahead of the strut. It is noticed that the increase in hydrogen jet pressure in the supersonic flow field improves the jet penetration rate in the lateral direction of the flow and also increases the total pressure loss as compared with the baseline injection pressure condition.
Practical implications
The outcome of this research provides the influence of fuel injection pressure variations in the supersonic combustion phenomenon of hypersonic vehicles.
Originality/value
This paper substantiates the effect of increasing hydrogen jet pressure in the reacting supersonic airstream on the performance of a scramjet combustor.
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Gautam Gupta, Akshay Ashok Kumar, R. Sivakumar and Jayaraman Kandasamy
This study aims to investigate the prevalence of shock boundary layer interaction (SBLI) in air-breathing intake system is highly undesirable since this leads to high pressure…
Abstract
Purpose
This study aims to investigate the prevalence of shock boundary layer interaction (SBLI) in air-breathing intake system is highly undesirable since this leads to high pressure gradients, typical stream mutilation and pressure drop. A novel flow control mechanism is incorporated in this research holding an array configuration of passive flow control device (micro ramps [MR]) that is adapted to improve the boundary layer stability.
Design/methodology/approach
Two geometric variants of the MR, namely, MR40 and MR80 is considered which reduce the pressure drop during SBLI. The incidence oblique shock wave angle of 34° is considered for the modelling. Large eddy simulation (LES) turbulence model was used with subgrid models of Wall modelled LES, Smagorinsky–Lilly to compute the unsteady effects of SBLI control using micro vortex generators. The unsteady results are compared with steady Reynold’s average Naviers–Stoke’s equation for calibrating the turbulence models.
Findings
The array configuration of MR80 reduces the pressure drop by 22% as compared with no ramp configuration and also reduces the flow distortion in hypersonic inlet. The most affected region of the MR is in the vicinity of center-line. Quantitative results prove that the upstream influence of the shock waves has been largely reduces by MR80 array configuration as compared to single MR80 pattern configuration. Different vortex structures found in the experiments was exclusively predicted using LES.
Originality/value
This paper substantiates the requirement of MR array configuration for transferring the momentum from free stream to the boundary layer and thereby energizing the boundary layer. This process of energization delays the flow separation in hypersonic flow.
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Rajesh Mavuri and R. Sivakumar
The swirl intensity imposed on the flow plays a vital role in aerodynamics, flame shape, flame stabilization and combustion intensity. In lean direct injection (LDI), the air and…
Abstract
Purpose
The swirl intensity imposed on the flow plays a vital role in aerodynamics, flame shape, flame stabilization and combustion intensity. In lean direct injection (LDI), the air and fuel are fed through separate channels, and the swirling air flows have a strong impact on fuel-air mixing and heat release. The literature indicates that the effects of swirling on helical axial LDI systems are limited to nonreacting flows studied through experimental methods, but not many studies have been reported on the reacting flows of a single swirler. The objectives of the paper are divided into two parts. The first part presents the role of swirl in nonreacting LDI systems and the second part describes spray combustion in LDI systems for low (swirl < 0.5) to high (swirl > 0.5) swirl numbers.
Design/methodology/approach
The numerical model incorporates all the necessary features of the single helical axial swirler, starting from the hollow circular section to the outlet of a long mixing chamber. The commercial solver FLUENT is used to predict the flow field around the axial swirler. The first step is to establish a numerical procedure (based on computational fluid dynamics [CFD]) to predict the nonreacting flow behavior for different swirlers and the CFD results are validated against literature data. The spray atomization, droplet evaporation and the effects of interaction between the two phases are modeled by implementing various spray submodels in FLUENT. The large Eddy simulation (LES) reacting flow results for a vane tip angle of 60° are compared with test data and presented at multiple cross planes.
Findings
The numerical simulations were carried out on a nonreacting single helical axial swirler for various vane tip angles, such as 40°, 50°, 55, and 60°, and the results were validated against test data. The centerline mean axial velocity and radial velocity profiles at several axial locations are in good agreement with the literature data. For reacting swirling flows, the experimental data is available only for a 60° vane tip angle. The S60 reacting flow LES mean predictions are compared at different cross planes. The axial momentum increases due to the liquid spray combustion in the gas phase and the reacting flow central recirculation zone is substantially shorter than the nonreacting flow. The impact of spray atomization due to interaction with the gas phase is verified, and the droplet mean diameter trends are consistent across different cross planes. The LES predictions of reacting flows for low to high swirls are investigated, and the effects on combustion performance are summarized.
Originality/value
The novelty of the paper is highlighted in two key conclusions. First, the paper presents numerical methods for studying the role of swirl in a nonreacting LDI system and validates the results against experimental data. Second, the effects of combustion on the gas phase, spray combustion modeling and droplet atomization are numerically established and compared with literature data for a 60° vane tip angle. In addition, the role of swirl in the reacting flow field for vane tip angles of 40°, 50° and 60° is numerically investigated, and its effect on flame stability, pressure drop and NOx emissions is presented. The paper describes LES grid guidelines for the LDI swirler and presents a numerical modeling approach that helps to develop a robust swirler design through a parametric investigation of swirler geometry. The methodology can be extended to study multi-element swirler configurations, to understand the effect of swirl on droplet breakup, momentum exchange with adjacent swirlers, flame propagationand emissions.
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Mavuri Rajesh and Sivakumar R.
For higher swirling flows (swirl > 0.5), flow confinement significantly impacts fluid flow, flame stability, flame length and heat transfer, especially when the confinement ratio…
Abstract
Purpose
For higher swirling flows (swirl > 0.5), flow confinement significantly impacts fluid flow, flame stability, flame length and heat transfer, especially when the confinement ratio is less than 9. Past numerical studies on helical axial swirler type systems are limited to non-reacting or reacting flows type Reynolds averaged Navier Stokes closure models, mostly are non-parametric studies. Effects of parametric studies like swirl angle and confinement on the unsteady flow field, either numerical or experimental, are very minimal. The purpose of this paper is to document modeling practices for a large eddy simulation (LES) type grid, predict the confinement effects of a single swirler lean direct injection (LDI) system and validate with literature data.
Design/methodology/approach
The first part of the paper discusses the approach followed for numerical modelling of LES with the minimum number of cells required across critical sections to capture the spectrum of turbulent energy with good accuracy. The numerical model includes all flow developing sections of the LDI swirler, right from the axial setting chamber to the exit of the flame tube, and its length is effectively modelled to match the experimental data. The computational model predicts unsteady features like vortex breakdown bubble, represented by a strong recirculation zone anchored downstream of the fuel nozzle. It is interesting to note that the LES is effective in predicting the secondary recirculation zones in the divergent section as well as at the corners of the tube wall.
Findings
The predictions of a single helical axial swirler with a vane tip angle of 60°, with a duct size of 2 × 2 square inches, are compared with the experimental data at several axial locations as well as with centerline data. Both mean and unsteady turbulent quantities obtained through the numerical simulations are validated with the experimental data (Cai et al., 2005). The methodology is extended to the confinements effect on mean flow characteristics. The time scale and length scale are useful parameters to get the desired results. The results show that with an increase in the confinement ratio, the recirculation length increases proportionally. A sample of three cases has been documented in this paper.
Originality/value
The novelty of the paper is the modelling practices (grid/unsteady models) for a parametric study of LDI are established, and the mean confinement effects are validated with experimental data. The spectrum of turbulent energies is well captured by LES, and trends are aligned with experimental data. The methodology can be extended to reacting flows also to study the effect of swirl angle, fuel injection on aerodynamics, droplet characteristics and emissions.
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Ahmed Benamor, Aissa Abidi-Saad, Ridha Mebrouk and Sarra Fatnassi
This study aims at investigating two-dimensional laminar flow of power-law fluids around three unconfined side-by-side cylinders.
Abstract
Purpose
This study aims at investigating two-dimensional laminar flow of power-law fluids around three unconfined side-by-side cylinders.
Design/methodology/approach
The numerical study is performed by solving the governing (continuity and momentum) equations using a finite volume-based code ANSYS Fluent. The numerical results have been presented for different combinations of the governing dimensionless parameters (dimensionless spacing, 1.2 = L = 4; Reynolds number, 0.1 = Re = 100; power-law index, 0.2 = n = 1.8). The dependence of the kinematic and macroscopic characteristics of the flow such as streamline patterns, distribution of the surface pressure coefficient, total drag coefficient with its components (pressure and friction) and total lift coefficient on these dimensionless parameters has been discussed in detail.
Findings
It is found that the separation of the flow and the apparition of the wake region accelerate as the dimensionless spacing decreases, the number of the cylinder increases and/or the fluid behavior moves from shear-thinning to Newtonian then to shear-thickening behavior. In addition, the distribution of the pressure coefficient on the surface of the cylinders presents a complex dependence on the fluid behavior index and Reynolds number when the dimensionless spacing between two adjacent cylinders is varied. At low Reynolds numbers, the drag coefficient of shear-thinning fluids is stronger than that of Newtonian fluids; this tendency decreases progressively with increasing of Re until a critical value; beyond the critical Re, the opposite trend is observed. The lift coefficient of the middle cylinder is null, whereas, the exterior cylinders experience opposite lift coefficients, which show a complex dependence on the dimensionless spacing, the Reynolds number and the power-law index.
Originality/value
The flow over bluff bodies is a practical engineering problem. In the literature, it can be seen that the previous studies on non-Newtonian fluids are limited to the flow over one or two cylinders (effect of an odd number of cylinders on each other). Besides that, the available results concerning the flow of Newtonian fluids over three cylinders are limited to the high Reynolds numbers region only. However, this work treats the flow of non-Newtonian power-law fluids past three circular cylinders in side-by-side arrangements under a wide range of Re. The outcome of the present study demonstrates that the augmentation of the geometry complexity to three cylinders (effect of pair surrounding cylinders on the surrounded ones in what concerns Von Karman Street phenomenon) causes a drastic change in the flow patterns and in the macroscopic characteristics. The present results may be used to predict the flow behavior around multiple side-by-side cylinders.
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T.V.S. Sekhar, R. Sivakumar and T.V.R. Ravi Kumar
To study the steady viscous incompressible electrically conducting fluid flow past a circular cylinder under the influence of an external magnetic field at high Reynolds numbers …
Abstract
Purpose
To study the steady viscous incompressible electrically conducting fluid flow past a circular cylinder under the influence of an external magnetic field at high Reynolds numbers (Re).
Design/methodology/approach
The finite difference method is applied to solve the governing non‐linear Navier‐Stokes equations. First order upwind difference scheme is applied to the convective terms. The multigrid method with coarse grid correction is used to enhance the convergence rate. The defect correction technique is employed to achieve the second order accuracy.
Findings
A non‐monotonic behavior in separation angle when N≥5 and separation length when N≥3 is found with the increase of external magnetic field. The drag coefficient is found to increase with increase of N. The pressure drag coefficient, total drag coefficient and rear pressure are found to exhibit a linear dependence with N0.5. The pressure Poisson equation is solved to find pressure fields in the flow region. It is found that the upstream base pressure increases with increase of external magnetic field while the downstream base pressure decreases with the increase of the external magnetic field.
Originality/value
The non‐monotonic behaviors in the separation angle and separation length at high Re are explained through pressure fields which are found first time for this problem. The linear dependence of the pressure drag coefficient, total drag coefficient and the pressure at rear stagnation point with N0.5 is in agreement with experimental findings.
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Ranjitha K., Sivakumar P. and Monica M.
This study aims to implement an improved version of the Chimp algorithm (IChimp) for load frequency control (LFC) of power system.
Abstract
Purpose
This study aims to implement an improved version of the Chimp algorithm (IChimp) for load frequency control (LFC) of power system.
Design/methodology/approach
This work was adopted by IChimp to optimize proportional integral derivative (PID) controller parameters used for the LFC of a two area interconnected thermal system.
Findings
The supremacy of proposed IChimp tuned PID controller over Chimp optimization, direct synthesis-based PID controller, internal model controller tuned PID controller and recent algorithm based PID controller was demonstrated.
Originality/value
IChimp has good convergence and better search ability. The IChimp optimized PID controller is the proposed controlling method, which ensured better performance in terms of converging behaviour, optimizing controller gains and steady-state response.
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This paper aims to extracted sericin from the cocoons of Bombyx mori silkworms, and sericin powder was applied onto drawn textured polyethylene terephthalate (PET) yarns as a spin…
Abstract
Purpose
This paper aims to extracted sericin from the cocoons of Bombyx mori silkworms, and sericin powder was applied onto drawn textured polyethylene terephthalate (PET) yarns as a spin finish. The reactivity on the surface of PET yarns was analyzed through Fourier transform infrared spectrophotometry–attenuated total reflectance (FTIR-ATR) and dyeing with methylene blue as a reactive dye. Also, investigations were conducted on the effects of sericin, citrc acid (CA) (as a crosslinking agent), and sodium hypophosphite (as a catalyst) concentrations on some properties of false-twist textured PET yarns.
Design/methodology/approach
A false-twist texturing machine (Scragg-Shirley minibulk, England) was used with the draw ratio of 1.05, heating temperature of 120°C, texturing speed of 100 m min−1 and applied twist of 3,000 TPM. The aqueous extraction of sericin was carried out by the boiling of the raw silk in distilled water with L:R: 40:1 for 120 min. The aqueous solution was filtered with a filter paper to remove the impurities and insoluble fibroin. Finally, the sericin solution was freeze-dried to obtain the sericin powder. The sericin solution was applied on the drawn textured PET yarns using the “pad-dry-cure” method.
Findings
Sericin fixation onto the PET yarns was confirmed by FTIR-ATR. The results showed that there were no significant changes in the tensile strength, linear density, crimp contraction and crimp modulus, elongation at break and shrinkage. In contrast, a substantial increase was observed in moisture regain, vertical wicking, dye uptake and ultraviolet protection. There was also a reduction just in the electrical resistivity, in the presence of sericin.
Originality/value
Although sericin has been known to have numerous beneficial properties, its application in textile industry as a spin finish has not been reported yet.
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Charanjit Singh, Davinder Singh and J.S. Khamba
Green Lean concepts offer methods for managing manufacturing organizations with the goal of improving organizational performance. Green Lean practices are good options to increase…
Abstract
Purpose
Green Lean concepts offer methods for managing manufacturing organizations with the goal of improving organizational performance. Green Lean practices are good options to increase the environmental and operational performance of manufacturing industries. However, there are some barriers to implement Green Lean in manufacturing industries. This paper aims to identify these barriers by reviewing the literature and analyze inter-relationships amongst selected barriers.
Design/methodology/approach
This paper deals with the identification of barriers to the adoption of Green Lean practices in manufacturing industries. Using the DEMATEL approach and using the insights of experts, a cause and effect relationship diagram was generated through which the effect of barriers was analyzed.
Findings
Twelve barriers were categorized in terms of cause and effect, and the interrelationships of barriers were also analyzed. Threshold value is calculated as 0.134 and the values lower than a were eliminated to obtain the digraph. “Resistance to change,” “lack of top management commitment” and “lack of training to employees” are the most prominent barriers on the basis of their prominent score.
Research limitations/implications
Analysis in the research is highly dependent on expert judgments and opinions may be biased. However, the initial matrix obtained from the experts is hindered by the ambiguity about some relationships. But this can be improved by using fuzzy and grey set theories. The barriers used for the analysis are not from a specific type of manufacturing industry.
Practical implications
The findings will help the manufacturing organizations to simplify the most important barriers, the least significant barriers and the relationships between these barriers. This Berlin knowledge will enable administrators to increase awareness of the barriers in Green Lean implementation. “The top management commitment” and “government support” are most important for the removal of barriers to Green Lean strategies.
Originality/value
Very few scholars have used the DEMATEL approach to examine the sequence of the barriers to Green Lean implementation. The present study attempts to incorporate the DEMATEL model to assess the sequence of barriers to the implementation of Green Lean. This study investigates the degree of influence of barriers on each other and categorizes the barriers into cause and effect groups. This study is also intended to pave the way for future research in the path of the elimination of barriers to Green Lean strategies.