Incoming Jet Research Articles

Drag reduction mechanism based on the aerospike-jet composite approach under different incoming dynamic pressures

The drag experienced by the nose of an aircraft varies significantly under different incoming flow conditions. In order to reduce the aerodynamic force on the nose of the (hypersonic) supersonic vehicle, the numerical simulation approach has been used to analyze the drag reduction laws and mechanisms of a blunt-body vehicle with the aerospike-counterflowing jet composite approach under different incoming flow dynamic pressures. The effects of two environments with H = 0.1 km and H = 30 km, as well as the influence of different incoming Mach numbers on the drag reduction at H = 0.1 km were investigated. The research has shown that there exists a minimum overall drag value for the vehicle under different dynamic pressures, while the variation in the wall pressure is related to the actual operating conditions. The recirculation zones at the aerospike and in front of the blunt body are important flow structures that affect the drag reduction. When the jet total pressure ratio increases, the position of the recirculation zone at the head of the drag reduction rod moves away from the central axis of the model. When the incoming flow dynamic pressure is higher, the separation point of the recirculation zone in front of the blunt body is located further downstream, and the reattachment point is related to the incoming flow and jet conditions, aligning with the trend of variation of the position of the maximum pressure on the blunt body wall. As it can effectively push away the shock wave, the enhanced drag reduction effect of the jet is significant when the incoming flow dynamic pressure is higher. However, the high jet pressure resulting from high dynamic pressure needs to be considered in the actual design. Furthermore, the complex turbulent flow field formed by the high dynamic pressure incoming flow and the jet is worthy of further study by means of the large eddy simulation.

Surface characteristics evolution under the controllable impact cycles of an interrupted discrete waterjet

The interrupted discrete waterjet (DWJ) offers advantages in surface treatment due to its exceptional load characteristics and high controllability. However, the surface characteristics of materials under controllable DWJ parameters have not been fully elucidated. This study delves into the surface morphology, roughness parameters, microhardness, residual stress, and distribution of crystal characteristics in both the depth and radial directions under 2400–36,000 impact cycles of DWJ through peening experiments and material characterization. The findings indicate that the surface morphology is influenced by high-frequency roughness components with limited impact cycles, while low-frequency waviness components gradually take precedence with more impact cycles. As impact cycles increase, certain roughness parameters such as Sq, S5p, S5v, and S10z initially rise until 21,600 cycles, after which they fluctuate within a specific range. Furthermore, DWJ peening leads to an increase in maximum hardness with impact cycles, with the depth of peak value transitioning from the surface layer to the subsurface. The residual compressive stress initially increases and then decreases with impact cycles. Under the experimental conditions, the maximum hardness reaches 268.1HV0.3, a 49.95 % increase from the original state, and the peak residual compressive stress reaches 297.7 MPa with a 310.2 % increase. As impact cycles continue to rise, a balance between material removal and surface hardening is achieved, resulting in the stabilization of maximum hardness and compressive stress as erosion strength grows. Following DWJ peening, there is an increase in the percentage of low-angle grain boundaries, along with enhanced grain refinement, increased geometrically necessary dislocation (GND) density, and the emergence of new phases. As the impact cycles increase, the effects of DWJ peening on crystal grains become more pronounced. Additionally, it has been observed that the lateral jetting influence extends further horizontally than in the depth direction of the incoming jet. It is considered that cyclic hardening and high strain rate effects (1.2 × 104) play significant roles in material hardening and failure.

Flow regime prediction of a self-oscillatory flow induced by a vertical jet in a heated cavity: Computational and analytical approach

Interaction effects between the inlet Reynolds number (250≤Rei≤3000) and the heat flux of the impingement wall (0.5≤q″≤20kW/m2) was investigated in a vertical self-excited oscillating jet confined by a heated cavity. The results revealed that some high amounts of q″ stop oscillating flow. Thus, this study developed a new prediction method based on an analytical approach to identify the threshold of flow regime transition from oscillatory to non-oscillatory based on Rei. To this aim, a new dimensionless number named Non-dimensional Effective Number (NEN) was introduced. The proposed NEN index refers to the ratio of the thermal power applied on the impingement wall to the effective momentum power of the incoming jet. The performance of the proposed index was examined and compared in vertical upward and downward-facing chambers for different heat flux values. Investigations indicated that the proposed analytical method and the new NEN index have a much lower computational cost, despite the very high accuracy (about 95 %) compared to the numerical results extracted from the OpenFOAM code. The results also demonstrated that vertical downward self-excited jets maintain oscillatory behavior regardless of the amount of q″. In this case, the frequency of oscillations varied linearly with Rei for Rei >2000.

The structure of cross-ventilation flow in an isolated cylindrical building: Numerical study

Cross-ventilation serves as an efficient means to expel pollutants and heat from buildings, requiring no energy consumption due to variations in wind pressure. The structure of the cross-ventilation flow significantly influences ventilation effectiveness. However, limited attention has been given to understanding the impact of a building's cross-section on the structure of cross-ventilation flow. This study aims to fill this gap by numerically investigating the cross-ventilation flow structure in an isolated cylindrical building. The numerical simulation results are validated against reported experimental data, indicating a negligible simulation error of 0.8 % in the volume ventilation rate. This attests to the accuracy of the numerical method in predicting cross-ventilation flow in isolated buildings. As airflow traverses the cylindrical building along the curved side walls, pressure loss diminishes, facilitating increased air inflow. This results in a more horizontal entry of the incoming jet compared to that in a square building. Analysis of Root-Mean-Square streamwise-velocity and turbulence kinetic energy reveals greater airflow fluctuation outdoors for the square building and increased turbulence indoors for the cylindrical building. Notably, the volume ventilation rate of the cylindrical building demonstrates an 8.3 % improvement. Furthermore, the air exchange rate in the cylindrical building surpasses that of the square building by 1.38 times.

New Jet impingement flow-scale sets wall approach, Proximity limits & wall-jet heat transfer

A new scale is here identified as dominant in laminar jet impingement flow and heat transfer, namely, the height of the stagnation zone, zw. This being the point at which the jet “senses” the approaching wall, which corresponds to the location of marginal static pressure rise above the impinged plate. It is shown that this new profile-specific scale emerges from the virtual origin concept in Glauert's wall-jet solution, and physically constrained expressions are derived for both. Reynolds analogy is then conducted for the cases of uniform-heat-flux and -wall-temperature. This leads to a new prediction of the wall-jet heat transfer, valid upon convergence to quasi-self-similarity – within a diameter or two of the stagnation point. The convergence distance depends on incoming velocity profile and flow rate, as captured by the new virtual origin expression. The analysis also reveals that the convergence to self-similarity is delayed in the uniform heat flux case, even though eventually heat transfer is about one-third higher.The new scale also led to a successful description of the deceleration during wall-approach, as an interpolation between near-wall (Homann solution) and far-field (inviscid flow) asymptotes. Consequently, the new scale is shown to give the proximity limits for nozzle-to-plate distance. This being the distance at which the incoming jet becomes distorted due to constriction and back-pressure. Here found to correspond to around 2/5 of the stagnation zone height.All these findings are confirmed and validated through simulations, experimental measurements and literature data; and simple expressions are derived for prediction and design purposes.

The Effect of Mechanical Circulatory Support on Blood Flow in the Ascending Aorta: A Combined Experimental and Computational Study.

Percutaneous mechanical circulatory support (MCS) devices are designed for short-term treatment in cases of acute decompensated heart failure as a bridge to transplant or recovery. Some of the known complications of MCS treatments are related to their hemodynamics in the aorta. The current study investigates the effect of MCS on the aortic flow. The study uses combined experimental and numerical methods to delineate complex flow structures. Particle image velocimetry (PIV) is used to capture the vortical and turbulent flow characteristics in a glass model of the human aorta. Computational fluid dynamics (CFD) analyses are used to complete the 3D flow in the aorta. Three specific MCS configurations are examined: a suction pump with a counterclockwise (CCW) rotating impeller, a suction pump with a clockwise (CW) rotating impeller, and a discharge pump with a straight jet. These models were examined under varying flow rates (1-2.5 L/min). The results show that the pump configuration strongly influences the flow in the thoracic aorta. The rotating impeller of the suction pump induces a dominant swirling flow in the aorta. The swirling flow distributes the incoming jet and reduces the turbulent intensity near the aortic valve and in the aorta. In addition, at high flow rates, the local vortices formed near the pump are washed downstream toward the aortic arch. Specifically, an MCS device with a CCW rotating impeller induces a non-physiological CCW helical flow in the descending aorta (which is opposite to the natural helical flow), while CW swirl combines better with the natural helical flow.

Plume Spreading Due to Floor Conditions of a Plunging Liquid Jet Using Stereographic Backlit Imaging

Abstract Plunging liquid jets are a multiphase flow studied to understand how gas is entrained in a liquid and the resulting mixing capabilities. From existing literature, it has been hypothesized that rising bubbles play a noticeable role in the multiphase hydrodynamics of the plunging liquid jet bubble plume and that separating the rising bubbles from the incoming liquid jet can result in a significant increase in the depth of the bubble plume. This study explores the effects of separating the incoming liquid jet from the rising bubble plume through floor interactions and compression effects due to a finite tank depth. This configuration is found in many natural and industrial systems, but not within published literature. Using existing theoretical models of infinite depth plunging liquid jet systems, which align reasonably well with captured baseline data, two models are developed for when floor interactions are present, one theoretical and one empirical. The models show a correlation between plume spread and floor interaction with the incoming plunging liquid jet bubble plume. Data acquired through stereographic backlit imaging over a range of flow rates show a reasonable agreement with the proposed models.

Simulation of supersonic jet flow past a blunt body in a laboratory experiment using computer vision

The complex flow of a supersonic jet (Mach number 2.4–2.5) around the blunt aerodynamic body (consisting of a cylinder with a diameter of 16 mm and a truncated cone) was studied using the high-speed shadowgraph technique and computer vision-based visual data processing. The problem considered is directly related to the rocket and space systems stages safe separation problem in a sufficiently dense atmosphere. For systems with a sequential arrangement of stages, their separation often occurs under the rocket engine jet action. The occurrence of lateral forces in violation of axial symmetry can lead to overturning of the discarded stage and undesirable interaction with the outgoing stage. The goals of the paper were to study the pulsation characteristics of the incoming supersonic jet streamlining the body, as well as the pulsations of the bow shock wave in both axisymmetric and asymmetric flows. The recording frame rate in the experiments was up to 775 000 fps. Computer vision and various machine learning approaches were used to process a large number of shadowgraph images. Canny edge detection and Hough transform, as well as a convolutional neural network (CNN) based on YOLOv2 architecture, were used to automatically track the position of the bow shock relative to the body. Jet sound generation was studied - the amplitude dependence on the distance from the nozzle and the evolution in time. The position of the bow shock relative to the streamlined body and flow pulsations over time were analyzed. Bow shock pulsation spectra at zero angle of attack were compared to those at a small angle of attack (α = 2.5°–3°). The power spectral density was also estimated. The slope of the spectra for the zero angle of attack case was found to be horizontal and the spectra for the small angle of attack case had a slope close to −5/3. The strongest of the measured bow shock frequencies were found to be close to those of the jet mixing layer pulsations. The hardware signal spectrum was also measured and this signal can be considered as noise. The described approach makes it possible to obtain the physical characteristics of the flow at any point of interest. It was also shown that the automation of flow visualization experiments using computer vision techniques allows to increase the speed of data processing and obtaining new physical information, which may be important for engineers developing aircraft and spacecraft technologies.

Effects of energy-share and ambient oxygen concentration on hydrogen-diesel dual-fuel direct-injection (H2DDI) combustion in compression-ignition conditions

This study investigates the ignition and combustion characteristics of interacting hydrogen (H2) and diesel surrogate jets under simulated compression-ignition engine conditions. The experimental setup includes two converging single-hole injectors in an optically accessible constant-volume combustion chamber (CVCC). The parameters varied in the study are fuel injection durations and ambient O2 concentrations (10 to 21 vol.%). The results show that a longer interaction between the diesel products and the H2 jet is required to achieve ignition of the H2 jet at lower O2 concentrations. Once ignited, the flame stabilises near or at the nozzle, except under the lowest ambient O2 condition of 10 vol.% where a lifted flame is observed. The lift-off response, however, is influenced by the relative injection duration of the fuels, with the interaction between the incoming H2 jet and the diesel combustion recession products possibly playing a role. The interaction between the jets also affects the recorded intensity and the distribution of the diesel fuel jet soot zone.

Numerical Analysis of Traditional and Hooped Pelton Runner at Various Operating Conditions

Pelton turbine is an impulse turbine that converts kinetic energy of incoming jet of water into mechanical energy. Due to impingement of high-speed jet on buckets, Pelton turbine experience high stress at the tip of bucket and at the connection of bucket and rim. To provide the structural strength to the runner, a hoop is attached to it which allows better distribution of forces. However, the impact of hoop on the hydraulic performance of runner is important to assess. For this, a numerical analysis based on Computational Fluid Dynamics has been performed on both traditional and hooped Pelton runner. Transient analysis has been done to calculate the efficiency of both runners under same boundary conditions. The analysis was performed at different openings of needle. Numerical study showed that the efficiency of hooped Pelton runner is less compared to traditional Pelton runner at higher and medium openings. However, at lower openings hooped runner is more efficient. The efficiency drop was in the range of 3.56% to 1.25%. Flow contours reveal that obstruction of fluid is more prominent at higher opening than lower openings, which is the main reason for efficiency drop. Hoop, despite giving structural strength to the runner, is detrimental to the hydraulic performance of traditional runner.

Experimental Investigation of Liquid Interface Stability During the Filling of a Tank in Microgravity

The storage of propellants in space as well as the transfer and filling of spacecraft tanks is a prerequisite for future long-term space exploration missions. In this work, the vented filling of a partially filled tank, which is envisioned as a spacecraft tank, was investigated experimentally under compensated gravity in the Bremen Drop Tower. Experiments were performed with a partially filled tank and a test liquid HFE-7500. The drop tower provides 9 s of compensated gravity. The shape of the free liquid surface inside a right circular cylinder changes from the normal gravity configuration to a free fall configuration during the test. The filling was initiated after 3.5 s and continued until the end at 9 s. The interaction of the incoming liquid jet with the liquid interface was studied for different volumetric flow rates. A stable, but not steady liquid interface was characterized by a deformation due to the incoming liquid jet and the formation of a geyser. The growth of the geyser and the following disintegration into liquid droplets indicated an unstable liquid interface. Subcritical, critical and supercritical regimes of the volumetric flow rates were identified to classify stable and unstable liquid interfaces. The critical Weber number was found to be 1.04, which corresponds to a critical volumetric flow rate of 1.30 mL s-1. This critical Weber number was compared with the existing literature. Additionally, the behaviour of the liquid interface during the reorientation of the liquid inside the tank was observed.

PLUME ANALYSIS OF PLUNGING LIQUID JETS WITH FLOOR INTERACTIONS USING STEREOGRAPHIC BACKLIT IMAGING

Plunging liquid jets occur when a liquid jet travels through a gas and enters a liquid pool. They are studied in order to understand and model the highly efficient gas-liquid mixing in the resulting bubble plume. Among the aspects of plunging jets studied, compression effects at the bottom or within the pool, while relatively common in application, remain less understood in current literature. The presence of a tank floor spreads the resultant bubble plume which reduces the flow resistance between the rising bubble plume and the incoming liquid jet. The effect of the tank floor on the overall entrainment and mixing is unknown. In order to understand the compression effects of the plume-floor interaction, a liquid-filled tank was designed to simulate multiple tank depths. This work describes the apparatus used to produce a plunging jet with floor effects, as well as the image analysis methodology for identifying and comparing plume formations. Data were collected for multiple liquid flow rates encompassing different entrainment regimes as well as multiple plate positions, varying the level of plume and base interaction. Stereographic backlit images were acquired and several different identification methods are described to better define and compare bubble plume features. Limitations in the image analysis procedures are also described.

An integrated active-passive solution for strengthening the functionality of a solar air heater

ABSTRACT Solar air heaters are the cheapest way to harness solar energy, but that’s changing as other ways progress. Jet impingement improves the performance of heating and cooling devices with minimal cost. Impinged air on a ribbed surface combines active and passive heat uptake. The present study article offers an experimental investigation of a rectangular conduit SAH built with impinging air and V-patterned cylindrical wiring ribs as barriers. The absorber plate was heated at 1000 W/m2 non-variably. The experimental tests are conducted for a variety of design configurations, including = 1 to 6, = 0.021 to 0.054, = 6 to 12, α = 30° to 75°, = 0.40, = 0.84, and = 0.064. The Reynolds number varied from 4000 to 16,500 throughout these experiments. At = 5, = 0.034, = 10, α = 60°, the optimal enhancement was reported. The observed results suggest that V-patterned ribs accelerate flow after the incoming jet impinges and travels along the absorber’s ribs, enhancing heat transfer. Thermal-hydraulic performance was also tested for all data value sets, and a value of 3.301 is the maximum value obtained within the parameter range examined in this study.

Experimental and numerical study on an enhanced swirl cooling with convergent tube wall and local dimple arrangements

This paper experimentally and numerically investigates an enhanced swirl cooling structure, featuring multiple connected convergent swirl tubes and dimpled wall. The dimpled swirl tube adopts a novel local dimpled wall scheme, only arranging dimple arrays under the tangential jets, which takes advantage of the heat transfer potential of the individual dimple. A counterpart multistage convergent swirl tube without dimples is also studied as a comparison baseline to clarify the action of local dimple arrays on swirling flow. The spatially resolved heat transfer data are measured by applying transient thermochromic liquid crystal (TLC) technique. Four channel Reynolds numbers (Re = 20,000 to 50,000) are tested based on the maximum tube parameters. The results show that the enhanced dimpled swirl tube performs a synergistic reinforcement of the high-speed swirling flow over the dimple arrays, which produces many local high Nusselt number patterns. Under the individual injection slot, the upstream dimples have a better enhanced heat transfer performance. For the studied working conditions, the globally averaged Nusselt number of the dimpled swirl tube can be increased by 6.0%–11.5% in comparison with the baseline convergent swirl tube. Besides, the dimpled wall also suppresses the swirl intensity, which leads to the weakening of wall-fluid shear stress action and the disappearance of downstream vortex breakdown, and consequently reduces the pressure loss by 2.0%–10.2%. Based on the well-validated CFD results, the dimpled wall under incoming jets redistributes the contribution of the near-wall turbulence and the forced convection due to the near-wall flow motion to the heat transfer enhancement in the swirl tube, which achieve an ideal cooling performance of high heat transfer in combination with low pressure loss. This provides a new inspiration for the design and optimization of swirl cooling device.

Incompressible flow through choke valve: An experimental and computational investigation

The flow within a control valve is complex, particularly for choke types with multiple entries. Despite the abundant use of control valves in pressure-reduction applications across various fields, there is lack of understanding of fluid flow behavior within such valves. Failure associated with vortex shedding and Flow-Induced Vibration (FIV) remains as a long-standing issue with operation of control (choke) valves. This industry-academia collaborative study constitutes a coupled computational and experimental methodology to analyze the complex flow within a choke valve under laminar inflow conditions. The investigation is conducted on a control valve, currently used in industry, at four specific choke positions. Incompressible Computational Fluid Dynamics (CFD) simulations are performed using water as fluid and Detached Eddy Simulation (DES) as turbulence model under two different laminar inlet flow rate (equivalent Reynolds number, Re, approximately 100 and 500). Experiments are carried out under the same conditions using Particle Image Velocimetry (PIV). The instantaneous and time-averaged (mean) vorticity and velocity contours are presented on four selected planar cross sections providing complementary information on the flow physics. Despite the complex geometry of the choke valve in question as well as the fluid flow developing within it, close agreement is found between the computational and experimental results. Both the studies reveal that, at low valve openings, when only the small ports are engaged, there forms a four-lobed vortical structure which is established upon collision of the incoming jets. The vortical structure of the flow is much more complex at higher valve openings when both the small and large ports are engaged. The inherent unsteadiness associated with turbulent flow within the valve chamber leads to flipping motion of the formed jets and vortex shedding; mechanisms of which are explained in detail in the paper. The frequency spectrum of the fluid flow is correspondingly assessed using Fast Fourier Transform (FFT) examining the dominant vibration modes and corresponding Strouhal numbers. The dominant frequency peaks found in computational and experimental studies can result in FIV and resonance failure of control valves in practice. The autocorrelation analysis and continuous wavelet transform have furthermore been augmented in signal processing of the data to illuminate the oscillatory behavior of the flow due to vortex shedding.

Quantification of the impact of RANS turbulence models on airflow distribution in horizontal planes of a generic building under cross-ventilation for prediction of indoor thermal comfort

Computational fluid dynamics (CFD) simulations based on the steady Reynolds-Averaged Navier-Stokes (RANS) approach are widely employed to predict airflow field and thermal comfort in cross-ventilated buildings. RANS models are highly sensitive to the selected turbulence parametrization. Although the impact of turbulence models on airflow distribution in the vertical center plane of a building has been studied, limited studies have focused on detailed analysis of horizontal planes.The current study investigated the impact of RANS turbulence models (Standard k-ε, Standard k-ω, Realizable k-ε, Renormalization group k-ε model) on indoor airflow distribution of horizontal planes in an isolated generic building. CFD simulations were validated with wind tunnel measurements. Airflow distribution in each turbulence model was quantitatively assessed in terms of the percentage area of a horizontal plane which holds a certain airflow speed (Au). The indoor thermal comfort in the horizontal planes was also evaluated with predicted mean vote (PMV). Moreover, the surface area, volume, angle, spreading width of incoming jets were studied.Best overall performance in validation was demonstrated by standard k-ε model. Turbulence models exhibited distinct airflow patterns and significant differences in Au, even in horizontal planes which showed similar results for validation metrics. Similar differences were observed in PMV distribution. This study provides new insight on the prediction of airflow distribution and thermal comfort in horizontal planes, by showcasing the necessity of acquiring wind tunnel data in carefully selected points in the horizontal planes (i.e. not limited to the vertical center plane) for CFD model validation.

Numerical research on cross-ventilation flow of a generic building in unsheltered and sheltered conditions: impact of cross-section

The performances of ventilation in the buildings with quadrate and cylindrical cross-sections are compared numerically. The incoming jet in the cylindrical unsheltered-building is more horizontal in comparison to the quadrate unsheltered-building. The dimensionless volume flow rates in the quadrate and cylindrical unsheltered-buildings are respectively 0.503 and 0.553. The incoming jet in the sheltered-buildings flows to the floors immediately. The velocity near the floor in the cylindrical sheltered-building is greater than that in the quadrate sheltered-building. The dimensionless volume flow rates in the quadrate and cylindrical sheltered-buildings are respectively 0.130 and 0.210.Comparing with the quadrate buildings, the ventilation rates in the cylindrical unsheltered and sheltered buildings increased by 10% and 61%.

Separation of conduction and convection heat transfer effects for a metal foamed flat plate impinged by a circular jet

The present study is concerned with an experimental investigation of the local heat transfer coefficient for an air jet impinging on a flat plate with porous foam (aluminum and resin foam) using a thin metal foil technique. The experiments are performed for the Reynolds number (based on a nozzle diameter) ranging from 10,000 to 25,000 and nozzle to plate spacing varying from 2 to 10 times the inner diameter of a nozzle. The thickness, porosity, and pore density used are 8 mm, 92%, and 20 pores per inch. The static wall pressure distribution for the smooth flat plate and a foamed flat plate is measured. An infrared thermal imaging technique is used for temperature distribution measurement. The wall static pressure distribution shows that the presence of the porous foam offers extra additional hydraulic resistance to an incoming jet. Metal foamed flat plate experiences an increase in heat transfer because of conduction caused by the metal foam and decrease in heat transfer because of additional hydraulic resistance. However, the resin foamed flat plate experiences only decreases heat transfer caused by the additional hydraulic resistance. Hence, the conduction effect experienced by the metal foamed flat plate can be separated. Region-wise correlations for Nusselt number based on the Reynolds number (Re), a non-dimensional radial distance (r/d)and nozzle to plate spacing (z/d) are proposed.

Remote Cooling of Rolls in Hot Rolling; Applicability to Other Processes

A novel method of cooling rolls in hot rolling is proposed. This method uses a combination of solid jet nozzles and specially shaped deflecting vanes. The vanes transform the incoming cylindrical water jet into a flat fan. Thereby, the coolant can be directed into hardly accessible locations whilst maintaining the optimal angle of impingement. The vanes allow for effectively cooling the roll surface near the rolling gap, which is otherwise not possible with classical flat fan nozzles. The jet impact is tangential due to the limited room for nozzle mounts or a coolant supply. The developed method was laboratory tested. A similar cooling efficiency was found between the vane and the flat fan nozzle. The latter was however mounted in a position impossible in the plant. The potential of the proposed cooling is, therefore, eminent. Apart from hot rolling, it could be exploited in other technological processes such as high pressure die casting, machining, turning, hot stamping, etc.

Experimental assessment of the impact of variation in jet fuel properties on spray flame liftoff height

Ensuring efficient and clean combustion performance of liquid-fueled engines requires comprehension of the influence of fuel composition and properties on flame behavior, such as flame liftoff height (LOH) and lean blowout limit (LBO). Spray flame stability is strongly affected by both the fuel reactivity and physical properties. Herein, the flame stability mechanism represented by LOH is investigated for seven jet turbine fuels, including surrogate, alternative, and conventional jet fuels, using a laboratory spray burner. Based on the experimental observations, the current work introduces a new analysis, which provides insight into the competing/complementing processes that occur in a multi-phase reacting system and highlights the key properties important in spray flame dynamics, accounting for both the fuel spray/vaporization as well as the chemical reactivity, to explain the relative differences in LOH of complex multicomponent fuels. Results show that spray flame stabilization occurs when there is a balance between the local spray burning velocity and the incoming jet velocity, which is strongly associated with laminar flame speed and the relative amount of liquid and gaseous fuel crossing the flame preheat region. Using a multicomponent droplet evaporation model, it was observed that preferential vaporization of the lighter and more reactive species of the simple surrogate fuels contribute to a shorter lifted flame as compared to fuels consisting of heavier and/or less reactive components. The LOH of real jet fuels showed strong sensitivity to droplet vaporization and mixing, which is controlled by the fuels’ volatility (i.e., boiling temperature at 50% distillation volume) and atomized droplet size, and to a lesser extent the reactivity represented by laminar flame speed. The enhanced linearity in the correlation of 50% vapor distilled compared to the other distillation cuts suggests that preferential vaporization could play an important role in defining the LOH stabilization mechanism even for more complex fuels.