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This experimental and numerical study investigates the stability and emission characteristics of the flameless combustion for various tangential and coaxial air entry configurations using biogas (60% CH4, 40% CO2) in an asymmetric vortex mesoscale furnace without preheating. It has examined three designs by varying the tangential and coaxial air entry (MF2T4A, MF4T4A, MF6T4A), global equivalence ratio (1.0), and thermal input (207 W) to highlight the impact of furnace configuration on flameless combustion. Temperature and exhaust species concentration measurements in the furnace and a visual inspection were used to conduct the investigation. It has demonstrated that the temperature and NOx emission generally decreases with decreasing O2. Interestingly, the non-premixed flameless combustion for MF6T4A configuration design behaves has an almost insignificant difference and is not very distinct from the other tangential entry configuration design cases. For example, these combustions are a fully flameless mode with a range of Φ = 1, producing an ultra-lower NOx due to the big mixing zone under this air–fuel arrangement. Furthermore, it is verified that the MF2T4A configuration design is the optimal design that provides a higher and uniform temperature, resulting in increased efficiency and ultra-low NOx emission. In contrast, for the case of coaxial entry without tangential configuration, it has combustion instability inside the mesoscale combustor due to an insufficient mixing zone under this coaxial air–fuel arrangement. Finally, the numerical analysis from computational fluid dynamics (CFD) is performed to predict and compare configuration design results. It found that the variations of NOx emissions depend on the variations of O2 and maximum temperature within the furnace rather than the average furnace temperature. Finally, the present study, non-premixed flameless combustion, approves that the tangential air-inlet configurations should be considered a critical operational parameter when designing furnaces. The results show that O2 (15%) recorded the maximum NOx emissions at 2.2 ppm, 0.92 ppm, and 0.52 ppm. In contrast, we recorded the lowest CO emissions at 0.0161 ppm, 1.29 ppm, and 130 ppm, in the cases of air entry configurations of MF2T4A, MF4T4A, and MF6T4A, respectively. Meanwhile, when the results reached the O2(5%) as the lowest concentrations in this research, NOx emissions were ultra-low values recorded between 1.20E-8 ppm and 1.27E-9 ppm. In contrast, CO emissions were different from each other and recorded a little high 692 ppm at 5% O2. [ABSTRACT FROM AUTHOR]

Laguerre–Gaussian beams are structured light beams with a donut-shaped symmetric intensity profile and a helical phase profile. The beam profile is defined by a quantized parameter known as the mode number which extends to infinity. The availability of unbounded modes makes these beams a promising candidate for next-generation optical computing, and optical communication technologies. The symmetric intensity profile of a Laguerre–Gaussian beam can be made asymmetric through certain techniques and these beams are known by the term 'asymmetric Laguerre–Gaussian beams'. Here, the asymmetricity adds another degree of freedom to the beam (apart from its mode number) which helps in encoding more information compared to a symmetric beam. However, in order to harness the benefits of all the available degrees of freedom, it is required to generate a large number of such beams in a multiplexed fashion. Here, we report the generation of such a large array of asymmetric Laguerre–Gaussian beams for the first time. Computer-generated holography and spatial multiplexing techniques were employed to generate a large array comprising of 12 × 16 = 192 asymmetric Laguerre–Gaussian beams with an arbitrary mode index and asymmetricity. [ABSTRACT FROM AUTHOR]

Laguerre–Gaussian beams are structured light beams with a donut-shaped symmetric intensity profile and a helical phase profile. The beam profile is defined by a quantized parameter known as the mode number which extends to infinity. The availability of unbounded modes makes these beams a promising candidate for next-generation optical computing, and optical communication technologies. The symmetric intensity profile of a Laguerre–Gaussian beam can be made asymmetric through certain techniques and these beams are known by the term ‘asymmetric Laguerre–Gaussian beams’. Here, the asymmetricity adds another degree of freedom to the beam (apart from its mode number) which helps in encoding more information compared to a symmetric beam. However, in order to harness the benefits of all the available degrees of freedom, it is required to generate a large number of such beams in a multiplexed fashion. Here, we report the generation of such a large array of asymmetric Laguerre–Gaussian beams for the first time. Computer-generated holography and spatial multiplexing techniques were employed to generate a large array comprising of 12 × 16 = 192 asymmetric Laguerre–Gaussian beams with an arbitrary mode index and asymmetricity.

This paper aims to investigate the side force on a cone–cylinder geometry at different angles of attack (α) by adopting experiments and computations. The cone–cylinder configuration had a length to diameter ratio (L/D) of 10, and a base diameter (D) of 25 mm. The nose shape had a fineness ratio of approximately 3. Results indicated that the side force increases with the increasing of the angle of attack. A circular ring was used to reduce the side force at different angles of attack. Using a smaller height ring (2% of local diameter) in the initial portion of the body did not reduce the side force significantly at lower angles of attack. However, a ring with larger height (5% of local diameter) placed at 2.5 times the diameter of the body from the tip reduced the side force at almost all the angles of attack.

This paper describes an experimental investigation of the initial growth of flow asymmetries over a slender body of revolution at high angles of attack with natural and disturbed noses. Time-resolved particle image velocimetry (PIV) is used to investigate the flow field around the body. Flow visualization clearly shows the formation of the asymmetric vortices. Instantaneous PIV shows that the amplified asymmetric disturbances lead to Kelvin–Helmholtz instability appearing first on one side, which increases the momentum exchange crossing the layer. As a result, the separation region shrinks which creates the initial vortex asymmetry. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the side force on a cone-cylinder geometry at different angles of attack (α) by adopting experiments and computations. The cone-cylinder configuration had a length to diameter ratio (L/D) of 10, and a base diameter (D) of 25 mm. The nose shape had a fineness ratio of approximately 3. Results indicated that the side force increases with the increasing of the angle of attack. A circular ring was used to reduce the side force at different angles of attack. Using a smaller height ring (2% of local diameter) in the initial portion of the body did not reduce the side force significantly at lower angles of attack. However, a ring with larger height (5% of local diameter) placed at 2.5 times the diameter of the body from the tip reduced the side force at almost all the angles of attack. [ABSTRACT FROM AUTHOR]

Measurements of moments were carried out on a slender body having a pointed forebody at lower velocities. The slender body had an ogive nose shape and an overall length to diameter ratio of 16. The angle of incidence was varied from low to moderate angles of attack in the pitch plane. The main objective of the present investigation was to measure the rolling moments on the slender body with and without the control technique. The side force was reduced using a rectangular cross-sectioned ringplaced suitably on the body, however, the slender body was found to experience rolling moments which may be catastrophic. [ABSTRACT FROM AUTHOR]

A free-surface vortex is a mass of water rotating around an axis perpendicular to the free surface. It can occur when withdrawing water from reservoirs or rivers at hydropower intakes with low submergence. Existing vortex models provide general information about the symmetric vortex structure. The vortex structure occurring in an approach flow at the critical submergence condition is examined in detail. In the laboratory, a steady air-core vortex over a bottom intake was created in a wide recirculating flume, in which the water depth, mean velocity of the approach flow and intake discharge could be adjusted. Flow visualization shows that the approach flow results in a non-symmetrical velocity distribution in the vortex throughout the flow depth. The detailed set of high-speed particle image velocimetry data in a series of horizontal and vertical planes was used to observe the formation and evolution of the three-dimensional flow structure of the strong air-core vortex and determine the origin of the vortex. Analysis of these data revealed a complex three-dimensional vortex structure due to the approach flow interacting with the air-core vortex forming a secondary vortex originating at the mixing zone upstream of the vortex, identified by a zero downstream velocity component, and feeding into the upstream side of the intake. [ABSTRACT FROM AUTHOR]

Investigations have been made adopting experiments and computations on an ogive-nosed slender body at different angles of attack and Reynolds number of 29,000 based on the model base diameter diameter. The results indicated an increase in the side force at large angles of attack, which is mainly due to the presence of asymmetric vortices in the leeward of the body. The inclusion of a rectangular cross-sectioned ring in the initial portion of the body reduced the side force at higher angles of attack. However, significant side force was experienced at lower angles of attack (30° < α < 40°). Use of a ring of 3% height was found to be suitable for reducing the side force at a higher angle of attack. From the results obtained it was observed that a ring if placed at a different axial location alters the flow field and changes the side force at higher angles of attack. Further studies indicated that placing of rings pair at an axial location of 3.5 and 4.5 times the base diameter reduced the side force to a very low value at all the angles of attack for the present shape of body and flow conditions. [ABSTRACT FROM AUTHOR]

Experiments and computations have been made to obtain the details of the flow field over a slender body at high angles of attack at a freestream velocity of 17 m/s corresponding to a Reynolds number of 2.9×104 based on the base diameter. Experiments indicated that the existence of side force at higher angles of attack is mainly due to the presence of asymmetric vortices in the leeward side. A rectangular cross-section circular ring placed at an axial distance of 3.5 times the base diameter reduced the side force at all the angles of attack. Investigations were made to obtain the effect of the height of the ring at an angle-of-attack of 50° where the side force experienced is relatively large. A ring placed at a distance of 3.5 times the base diameter alters the initial vortices and hence helps in substantial reduction of the side force. Studies with rings of different heights indicate that a ring having a height of 3% of the local diameter reduced the side force at almost all the angles of attack for the present flow conditions and provided the least disturbance to the lift and drag of the body. [ABSTRACT FROM PUBLISHER]

The self-excited oscillation of a wing body induced by fore-body vortices was studied experimentally. To avoid interference, the experimental procedure is divided into two steps: First, the time histories of the self-excited oscillations were obtained using a free-to-roll rig. Then, these time histories were replicated using a forced-to-roll rig driven by a servomotor. Surface pressure and vortex wake are measured simultaneously during the prescribed oscillatory motions. The free-to-roll results show that the tip imperfection significantly influences the rolling motion pattern of a wing body and that the wing body can exhibit limit-cycle oscillations, fixed-point attractors, and apparent chaotic oscillations as the azimuthal angle of the artificial perturbation is varied. The measurements of surface pressures and flow fields indicate that the oscillatory types depend on the switching modes of fore-body vortices with roll angle, and the switching modes are determined by locations of tip perturbations. Furthermore, the fore-body vortices exhibit apparent dynamic hysteresis in vertical position, which further influences the wing flows, and the dynamic hysteresis of flows yields the damping moments sustaining the oscillations. By analyzing the reason for the formation of the rolling moments for sustaining the self-excited oscillations, the flow physics for each type of motion was revealed. [ABSTRACT FROM AUTHOR]

Based on the determinability of asymmetric vortices flow over slender body under changeless round grain at high angle of attack, the effect of microblowing set in special position on the behaviors of asymmetric flow is discussed in this paper, including blowing momentum and circumferential locations of the microblowing hole of 0.5 mm in diameter on nose tip. A new kind of active control technique, named perturbation-combined active control technique, which combines the micro-grain and micro-blowing perturbation, was proposed on the basis of the above. This control technique can not only change the sign of side force of slender body arbitrarily through changing the vortices positions between yaw-left and yaw-right configuration, but also can make the magnitude of side force variable gradually even at bistable state of asymmetric vortex. Finally, the interferential mechanism of the perturbation-combined active control technique has also been concluded from this paper. The tests have been conducted at low speed wind tunnel with subcritical Reynolds number of 1.05×10 at angle of attack α=50° in Beihang University, Beijing, China. [ABSTRACT FROM AUTHOR]

Forward blowing from a pair of plasma actuators on the leeward surface and near the apex is used to switch the asymmetric vortex pair over a cone of semi-apex angle 10° at high angles of attack. Wind tunnel pressure measurements show that by appropriate design of the actuators and appropriate choice of the AC voltage and frequency, side forces and yawing moments of opposite signs can be obtained at a given angle of attack by activating one of the plasma actuators. Further work is suggested. [ABSTRACT FROM AUTHOR]

Abstract: A numerical study on flows around a slender body of revolution at a high angle of attack is conducted to investigate the influence of strength and circumferential angle of perturbation on flow asymmetry. A source term model is applied to simulate a real geometrical perturbation near the tip of the slender body. It can greatly facilitate the adjustment of perturbation strength. The results show that the bistable phenomenon does not appear any more at a small perturbation strength. For different perturbation strengths, the energy of the asymmetric perturbation flow experiences a similar spatial exponential growth regime with the same growth rate. The appearance of the bistable phenomenon is closely related to nonlinear saturation of the perturbation flow as perturbation strength increases. [Copyright &y& Elsevier]

• The novel analytical asymmetric vortex solution of 2D GPE is derived. • The oscillation mode of the asymmetric vortex is identified. • The theoretical results obtained can be used to guide experimental investigation on asymmetric vortex. We studied the evolution of an asymmetric solitary vortex in a two-dimensional Bose-Einstein condensate starting from a quasi-one dimensional state with external harmonic trapping potential modulation. We derived the analytical solution of the asymmetric solitary vortex based on the two-dimensional Gross-Pitaevskii equation model and variational method. Furthermore, we identified the oscillation mode between the extreme asymmetric state and circular symmetric state for the derived solitary vortex. The obtained theoretical results can be used as guides for relevant experimental studies of asymmetric solitary vortices under similar physical conditions. [ABSTRACT FROM AUTHOR]