Jet Diameter Research Articles

Beamforming with modified steering vectors for jet noise source location

Prof. Krish Ahuja has a longstanding interest in jet noise source location. His work in this area is grounded in the idea that if the assumed source location is correct, then the sound should obey the inverse square law relative to that point and the phase should be constant along lines originating at that point. He applied this with, conceptually, one microphone in 1985 and two microphones in 1998. In 2006 he commissioned a beamforming system, Array 48, from OptiNav, Inc. His student, Nick Breen, used this to measure subsonic jet noise source location in detail. The NASA-Glenn Research Center also purchased an Array 48. In the current work, a jet noise data set measured by Gary Podboy using Glenn’s array in 2008 is revisited with a new beamforming algorithm, Robust Functional Beamforming, to further support Tam’s two-source model and Breen’s source location. Beamforming with modified steering vectors is performed to measure the parameters of the wavepacket source model from the far field. This process suggested replacing the wavepacket spatial length parameter with a temporal lifetime parameter. Another steering vector modification aimed to measure modes with odd spinning order. It seems to have found them at an apparent location 10 jet diameters removed from the jet, laterally. This is tentatively interpreted as a Mach radius phenomenon like one observed by Csaba Horvath at NASA-Glenn, also using Array 48, to study counter-rotating propeller noise. In an observation unrelated to beamforming, the excess noise measured at 40° from the jet axis as compared with the 90° angle, is fully contained in the first few cross spectral matrix eigenvalues, or Spectral Proper Orthogonal Decomposition modes, in some cases.

Influence of Spatial Characteristic Parameters of Film Cooling Holes on the Strength of Turbine Blade

In order to improve the fatigue resistance of turbine blades with special-shaped film cooling holes in real working environments, the spatial geometric characteristics of the gas film holes are studied by using the numerical calculation method of gas-thermal-solid depth coupling, which is based on the spatial geometric characteristics of special-shaped film cooling holes. Then, the influence of stress level and durable strength at the hole edge is developed, which includes the parameters of the film jet angle, the flow direction divergence angle, the span-wise divergence angle, and the pore diameter on the film cooling holes. The results show that the flow direction expansion angle and the spanwise expansion angle are the most significant impacts on the hole edge stress at the same pore diameter and film jet angle. Compared with the cylindrical gas film hole, it is decreased by about 9.3% to 25.8%, which is the hole edge equivalent stress of the special-shaped gas film hole. The durable strength of the hole edge increases by about 11.1% to 25.2%.

Desain Turbin Pelton Kapasitas 26 kW pada Pembangkit Listrik Tenaga Mikrohidro (Studi Kasus: Kampung Nehibe)

The need for electrical energy in Nehibe village is currently increasing along with the increase in population and new households. The demand for electricity in this village reaches 18 kW, with an average power per household of 450 VA. The problem is that Hachakwa Nehibe Micro Hydro Power Plant (PLTMH), which is very close to the village, has a capacity of only 10 kW. Based on that problem, this study aims to design a peltor turbine with two nozzles for the new 26 kW PLTMH. This power plant uses the water from the Tena Mroway and Yora Mroway rivers, which are located 2 km from the end of the village, as a new source of energy. This design of the turbine is based on the mathematical equations, measurement data of the head, and the flow of the rivers. This research shows that the Pelton turbine with two nozzles (nj), 0.032 meters of jet diameter (Dj), 0.330 meters of runner diameter (Dr), 0.096 meters of bucket diameter, and 21 buckets can produce 26 kW of power with 60 ltr/sec of river flow and 77 meters of head height. This specialization can be used to develop the new PLTMH in Nahibe Village.

Effect of dry ice jet velocity on cooling characteristics of electronic chip based on optimized geometry

ABSTRACT Efficient chip cooling has become particularly important with the rapid development of high heat flux electronic chips. In this study, a cooling system for electronic chips using dry ice as the cooling medium is developed. The combination of jet impingement and phase change sublimation was employed to achieve efficient cooling by utilizing the Joule-Thomson effect to generate dry ice. The impact of the ratio of heatsink height to inlet diameter (H/D) and dry ice jet velocity on the heat transfer characteristics of the heatsink is investigated by theoretical calculations and experimental tests. The results showed that the optimal heat transfer coefficient was achieved when H/D was 4, 12.76% to 43.28% higher than other H/D values. The chip temperature could be maintained below 38.69°C, which was 8.79% to 36.62% lower than other H/D values, and the heat flux reached 428.92W/cm2. The chip temperature could be effectively regulated by controlling the dry ice flow rate. Furthermore, a comparison with other cooling methods indicated that the dry ice jet cooling system was more suitable for cooling high heat flux electronic devices. The research findings laid the foundation for dry ice cooling of high heat flux chips.

Air-bubble entrainment by translating turbulent jets in stagnant water

This paper presents an experimental study on air-bubble entrainment in quiescent water by translating circular turbulent jets. The jet diameters, plunging heights, impact velocities, and translating velocities were varied during the experiments to investigate their relative effect on the bubble characteristics. The experimental observations reveal that the jet translation affects the air bubble entrainment mechanism and the distribution of bubble size. A rotating cavity forms around the plunging jet due to the translation of the jet. Depending on the translating velocity, the air bubble emanates from the cusp of the cavity and the downstream water surface meniscus with the jet. The bubble swarm produced by the translating jet exhibits vortex shedding with Strouhal numbers between 0.22 and 0.27, comparable to a circular cylinder in cross-flow. The peak of the bubble size distribution varies between 0.5 and 1.5 mm, while the Sauter mean diameter varies between 1.8 and 2.8 mm. The maximum penetration depth of bubbles is found to be a function of the jet impact to translating velocity ratio, and the Capillary number of the air–water interface. The spatial distribution of bubbles along the plume cross section exhibits Gaussian distributions. Finally, the terminal rising velocity of the bubbles shows no obvious effect of the jet translation.

Study on the Effect of Structural Parameters of Volume Control Tank on Gas–Liquid Mass Transfer

The volume control tank (VCT) is an important facility in the primary circuit of nuclear power plants. During the normal operation of nuclear power plants, the mass transfer between the gas and liquid phases occurs in the VCT at all times. It is driven by submerged jets, which may cause potential risks to the operational safety of nuclear power plants. It is necessary to conduct an in-depth study to gain a deeper understanding of the gas–liquid mass transfer behavior in the VCT. In this paper, a new gas–liquid mass transfer model is developed that combines a surface divergence model with a CFD model to accurately simulate the mass transfer process of the gas phase into the liquid phase. The simulation data were verified by the experimental results. The deviation between the simulation results and experimental results is less than 6.55%. Based on this model, a simulation study was carried out for the effect of structural parameters of the VCT on gas–liquid mass transfer. The results show that the double-vortex structure above the jet inlet, the surface jet at the gas–liquid interface, and the vortex at the end of the jet are the three factors dominating the gas–liquid mass transfer in the VCT. The gas–liquid mass transfer can be influenced by the jet diameter since the jet diameter has a remarkable effect on the Kolmogorov scale and the macroscopic flow field structure. Moreover, both the Kolmogorov scale and the macroscopic flow field structure can be affected by the jet height. However, these two effects cancel each other out. Thus, the influence of the jet height on the gas–liquid mass transfer rate is negligible.

A numerical investigation of hydrogen impingement-effusion array jet for a heat sink cooling using solid/porous fins: A thermo-hydrodynamic analysis

Increasing the aim of hydrogen use as fuel in vehicles motivates applying it to other critical requirements, such as cooling, owing to its thermal properties. Therefore, the effect of applying hydrogen impingement jets for cooling a hot surface of electrical devices, such as a prismatic battery, is investigated in this numerical study. The dependent variables are the volumetric flow rate, the jet distance from the target to the jet diameter, the coolant type, and the fins configuration, called in-line and staggered, and types, as solid or porous. The convective heat transfer coefficient, thermal resistance, pressure drop, and temperature and velocity distribution for the studied cases are considered. The simulation is conducted using the SST k-ω turbulence model, SIMPLE algorithm, and second-order method for discretization differential equations. Applying hydrogen as the coolant decreases the maximum temperature up to 2% and increases heat transfer by about 10%, while it mitigates the pressure drop by a factor of 1/12 if compared to air coolant. Further, inserting porous fins improves heat transfer by about 10% and 17%, respectively for air and hydrogen coolant in comparison with the case without fins. The fin decreases the temperature on the root and makes the recirculation zones.

The Displacements Study of Birch Veneer Layers from Composition of Plywood during Water Jet Cutting Using the Finite Element Method (FEA).

This paper presents a study of the deformations of the birch veneer layer of plywood composed of veneer sheets, each with a thickness of 1.4 mm. Displacements in the longitudinal and transverse directions were analyzed in each layer of veneer from the composition of the board. Cutting pressure was applied to the surface equal to the diameter of the water jet, located in the center of the laminated wood board. Finite element analysis (FEA) does not study the breaking of the material or its elastic deformation, but only what happens from a static point of view when maximum pressure acts on the board, which causes detachment of the veneer particles. The results of the finite element analysis indicate maximum values of 0.0012 mm in the longitudinal direction of the board located in the proximity of the application of the maximum force of the water jet. Additionally, in order to analyze the recorded differences between both longitudinal and transversal displacements, estimation of statistical parameters with 95% confidence intervals (CI) was applied. The comparative results indicate that the differences are not significant for the displacements under study.

Numerical study of electrohydrodynamic atomization considering liquid wetting and corona discharge effects

In this paper, the behavior of the cone-jet mode of fluid by electrohydrodynamic atomization (electrospray) is numerically simulated and investigated with the effect of liquid wetting and corona discharge effects. The simulation was performed with contact angle condition to fit the Taylor cone shape by experiments. Experimental data are provided to verify and validate the numerical method, followed by additional analyses on the effects of electrical conductivity, surface tension, flow rate, and fluid viscosity on the electrospray characteristics, including spray current and jet diameter. Numerical results by simulations are in reasonable agreement with experiments and consistent with the literature. Analyses on different contact angles suggest potentially major impacts of this factor on the cone-jet mode in high voltage and low flow rate circumstances. Furthermore, the influence of corona discharge on electrospray is also investigated by both electrospray–corona simulation and experiment using a high-speed camera, yielding a significant improvement in the numerical prediction for Taylor cone formation. Numerical results indicate that liquid wetting on capillary nozzles would be a vital factor for the Taylor cone formation in numerical electrospray–corona discharge studies.

Research on PTFE/Al reactive jet formation of shaped charge

During the PTFE/Al reactive shaped charge jet formation, the burst wave generated by the explosion of the explosive is sufficient to achieve the ignition conditions of the reactive materials (RMS). As a result, the RMS will react, resulting in an energy loss from the reactive jet. In order to research the forming features of PTFE/Al reactive jet and the energy loss during the jet formation, a PTFE/Al reactive liner with a diameter of 74 mm was prepared and an X-ray pulses photography experiment was performed on the jet formation. And the parameters of Johnson-Cook constitutive model of RMS were obtained through quasi-static experiments and Hopkinson pressure bar experiments. The jet formation were simulated, and the AUTODYN secondary development technology was used. The results show that the secondary development technology can intuitively show the reaction of the active material during the jet formation. The PTFE/Al reactive jet is less cohesive, its jet diameter is thicker, and the morphology is divergent. The reactive materials reacted during the PTFE/Al reactive shaped charge jet formation. And during the reactive jet formation, the inner layer of the liner collided. Therefore, most of the chemical reactions occur inside the reactive jet.

Effect of Rib Blockage Ratio and Arrangements on Impingement Heat Transfer in Double-Wall Cooling

Abstract A numerical study was conducted on the multiple jet impingement heat transfer of the double-wall cooling with high blockage ratio ribs of various configurations. Three different blockage ratios (BR = 0.2, 0.3, and 0.5) and two rib arrangements relative to the effusion holes (l/Sx = 0.25 and 0.75) were thoroughly examined using the RANS method with the SST–KIC turbulence model, considering the Kato–Launder modification (K), intermittency (I), and crossflow (C) transition effects. The ratio of jet-to-target plate spacing to jet diameter (H/d) was fixed to be 1, and Reynolds numbers varied in the range of 4000–16,000. Furthermore, the computed data on the rib roughed wall were also compared with those on a flat plate for the double-wall cooling. The results demonstrate that the installation of the high blockage ribs significantly decreases the detrimental crossflow effect due to the blockage effect of the ribs and intensively disturbs the jet flow in flow passing over the ribs, thereby enhancing the heat transfer performance. For the impingement/effusion cooling, the arrangement of the rib downstream of the effusion holes (l/Sx = 0.25) shows more advantages, and the heat transfer level rises quickly as BR increases. The best thermal-hydraulic performance and heat transfer uniformity on the rib roughed target plate is both obtained at BR = 0.3, which can be increased by up to 10% and 8%, respectively, compared to those on the flat plate.

Self-oscillating jets in cooling applications

In the present computational study, an assessment of self-oscillating jets for use in cooling applications is investigated. The jet exits from a square nozzle into a narrow rectangular cavity at a Reynolds number of 54,000 based on nozzle hydraulic diameter and average jet exit velocity. The heated devices, such as electronic chips, are located externally on the surface of the cavity. A three-dimensional numerical simulation of the flow is conducted by solving the unsteady Reynolds-Averaged Navier-Stokes and energy equations to assess the thermal features of the flow field. The unsteady Elliptic Blending Reynolds Stress Model, which consists of transport equations for each of the stress tensor components, was used to model turbulence. The cooling performance of a self-oscillating jet is compared with that of a wall jet and a channel flow for the same flow conditions and the same arrangement of the hot devices. The cooling efficacy of two different arrangements of the heated devices is also evaluated. The self-oscillating jet provides a higher heat transfer for the heated blocks which are located farther from the central region, while the wall jet improves heat transfer around the central region. Self-oscillating jets can improve heat transfer over a larger area when the heated devices are aligned orthogonal to the axis of the nozzle. On a Nusselt number comparative basis, the channel flow provides the least desirable heat transfer performance.

Large eddy simulation of a row of impinging jets with upstream crossflow using the lattice Boltzmann method

Large eddy simulations of a row of seven jets emerging from a perforated pipe and impinging on a flat heated plate were carried out using a compressible hybrid thermal lattice Boltzmann solver. The average Reynolds number of the emerging jets was 5000, with an exit-to-plate distance of 3 jet diameters. Two levels of upstream crossflow were simulated: one with weak cross flow, with a velocity ratio of ≈9.7, and one with strong cross flow, with a velocity ratio of ≈2. The flow field and heat transfer statistics were validated against experimental PIV and infrared thermography data from a recent study, showing good agreement. The effect of varying the Mach number on the wall heat transfer was subsequently tested. It was found that an increased Mach number lead to an increased value of the Nusselt number near the stagnation points.

Experimental investigation on debris bed formation from metallic melt coolant interactions

Motivated by risk quantification of severe core meltdown accidents which may occur light water reactors, an extensive DEFOR (DEbris FORmation) test series with various molten oxidic materials was conducted previously at Royal Institute of Technology to investigate the characteristics of debris beds formed from oxidic melt-water interactions, which are important to the coolability of debris beds and thus the retention of core melt. Yet, little attention has been paid to metallic melt which exist in the core melt. The present study is intended to fill in the knowledge gap, i.e., to characterize metallic melt-water interactions when a melt jet falls into a deep water pool. Nine DEFOR-M tests are carried out to clarify the effects of melt jet diameter, free fall height and water pool depth on metallic debris formation characteristics. Molten tin of 20 kg is employed as the simulant of metallic melt. A melt sensor and a mass sensor are installed to detect the discharging period of coherent jet and the mass accumulation of debris bed, respectively. A high-speed camera is applied to record the process of jet breakup, debris fragmentation and solidification, and debris bed formation. The experimental results show that the water pool depth has a significant influence on steam explosion and debris bed formation characteristics. Moreover, the jet breakup length is sensitive to jet diameter and free fall height. Finally, the features of metallic debris beds are compared with those of oxidic ones in respects of debris bed's configuration and porosity, particles' morphology and size distribution.

Simulation and neural network analysis of spreading the oblique fuel jet impinging onto concave walls

A series of numerical simulations of oblique-jet impinging onto concave walls are carried out to gain insight into the formation process of the liquid fuel film in a liquid film cooling thrust chamber. Moreover, the influence of jet and wall surface parameters on spreading the fuel film is investigated. The volume-of-fluid method is employed to capture the spreading process of liquid film formation after an oblique jet impacts the curved surface. Furthermore, the neural network model is developed to analyze the effects of jet diameter (0.2 mm ≤ d ≤ 0.6 mm), jet velocity (15 m/s ≤ v ≤ 20 m/s), impingement angle (15°≤β ≤ 30°), equilibrium contact angle (45°≤θe≤75°), curvature radius (22.5 mm ≤ R ≤ 67.5 mm), and surface roughness (3.2 μm ≤ Ra ≤ 16μm) on the fuel film's spreading length and maximum width based on Radial Basis Function. The results show that the liquid fuel film gradually stabilizes from upstream to downstream during spreading and the circumferential spreading of the liquid film is at its greatest when all the forces in the circumferential direction are in equilibrium. The jet diameter has the most significant effect on film spreading among jet parameters. Doubling the jet diameter at least doubles the film width and length. The effect of jet angle and velocity on film spreading is also magnified at larger jet diameters. Compared to other surface parameters, a change in the wall contact angle has the most marked effect on the spreading of the film. Lastly, the wall radius of curvature between 40 mm and 50 mm is more favorable for obtaining larger film lengths.

Numerical study of heat transfer enhancement over a rotating surface. Part I: Effect of pin-fin shapes

Rotating machinery like gas turbine engines consist of rotating components like gas turbine disks that are exposed to high thermal loads and stresses due to centrifugal force acting on them, and thus effective cooling is essential. The disks are additionally exposed to hot turbine gas ingress as an adverse pressure gradient is created in the stator-rotor cavity due to outward pumping of near-disk flow. Impingement of a coolant jet on such a surface can effectively provide cooling and also counter this adverse gradient. There also exists a circular relative velocity between the disk and wall-jet formed by impinging air as well as the air in the disk vicinity. Thus, the study of heat transfer under rotating conditions becomes important. With the advent of advanced manufacturing techniques, it is possible to produce disks with novel heat transfer enhancement features such as pin-fins which have not been previously explored. They create unique flow features in addition to increasing the surface area. The present study numerically investigates the heat transfer over rotating surfaces under jet impingement with square, triangular, cylindrical and dome-shaped pin-fins. This will inform the optimization of pin geometry for better heat transfer effectiveness and uniformity. Three different jet Reynolds numbers between 5000 and 18000 based on the jet diameter have been studied for three different Rotational Reynolds numbers based on the disk diameter. Transient non-conjugate heat transfer analysis was conducted, and the technique was compared with experimental results on square pin-fins and a smooth circular disk. The heat transfer enhancement greatly depends on the flow separation and pin area normal to the flow. A heat transfer enhancement of close to 2.2 was observed for triangular fins for the lowest rotation speed, for the highest rotation speed, the highest enhancement of close to 1.7 was observed in the cylindrical pins.

NUMERICAL INVESTIGATION OF PLATE COOLING USING MULTIPLE IMPINGING JETS IN DIFFERENT ALIGNMENTS

In this study, convective heat transfer by multiple impinging jet arrays in different arrangements is numerically investigated using Computational Fluid Dynamics (CFD). Computational domain consists of multiple jet array either in inline or staggered alignment and a target plate to be cooled by impinging jets. Distance between the jet array and the target plate is kept constant at H=28 mm. Diameter of circular jet nozzles is fixed at D=5 mm for all configurations. Effects of jet Reynolds number (Rej), spacing between circular jets and the alignment of the jet nozzles on aerothermal performance are parametrically investigated in the scope of this study. For staggered and inline alignments of the jet nozzles, Rej ranges from 5000 to 20000 and the ratio of the spacing to the jet diameter (s/D) changes between 2 and 6. CFD calculations are performed using finite volume based ANSYS-Fluent flow solver. Simulations are conducted for incompressible, steady and turbulent flow using k-ω SST turbulence model with ideal gas assumption for density and Sutherland law for viscosity. After intensive mesh convergence and validation tests, appropriate mesh resolution is determined and parametric investigations are performed. The study reveals that most dominant parameter for plate cooling is Rej followed by spacing between jets and finally jet alignment. For all Rej, inline jet nozzle alignment provides 15% higher average heat transfer rate than staggered alignment when s/D is close to the lower limit. However, it is shown that jet alignment does not affect thermal performance when s/D is higher.

Experimental analysis of thermal performance of SAH with impinging jet having varying length of perforated jet plate

An experimental setup of an impinging jet solar air heater (IJSAH) was developed to study its thermal and frictional characteristics. Six cases were analysed with the jet holes spanning different lengths across the jet plate. For cases 1 and 2, jet holes spanned 100% and 80% of the length of the jet plate while having jet diameter equal to 3 mm. For cases 3,4, and 5, jet holes were drilled up to 100%, 80%, and 60% of the entire length and the diameter was increased to 6 mm. For case 6, jet holes were drilled up to 100% while keeping jet diameter equal to 9 mm. For each case, variation in Nusselt number, friction factor and temperature rise of the fluid was evaluated for Reynolds number in the range 4913 to 13,103. The efficiency and thermo-hydraulic performance factor with each case were compared. It was concluded that IJSAH with reduced length of drilled section (case 5) developed similar performance to IJSAH having completely perforated jet plate (case 1) while developing significantly lower friction factor. The temperature rise of the fluid and the friction factor developed for case 5 were around 10% and 40% lower than case 1, respectively.

Fluid flow and heat transfer characteristics of three-dimensional slot film cooling in an annular combustor

Film cooling methodologies in air-breathing gas turbines have been evolving for many decades. In the present work, a combined experimental and numerical parametric study is conducted to investigate the three-dimensional slot film cooling of an annular combustor. The experimental investigation is conducted to understand the fluid flow and heat transfer phenomenon of the film cooling and to validate the numerical study under laboratory conditions (low temperature and pressure). Transient infrared thermography is used to estimate both adiabatic film-cooling effectiveness (ηad) and heat transfer coefficient (h) simultaneously using a semi-infinite approximation method. The blowing ratios considered in the study are in the range of 0.5 to 5. The experimental results showed that film-cooling effectiveness (ηad) enhanced with an increase in the blowing ratio from 0.5 to 2 and deteriorated beyond BR = 2 due to the adverse effects of turbulence. A parametric study is conducted numerically to understand the effect of flow and geometrical parameters under actual engine conditions (high temperature and pressure). The parameters considered are slot Reynolds number (Res), slot jet diameter (d), slot jet pitch (p), lip taper angle (α), lip length (L), and slot jet injection angle (β). For the considered parameters, numerical results showed that the slot jet diameter (d) = 2 mm, dimensionless slot jet pitch (p/d) = 2, slot jet injection angle (β)=20o and dimensionless lip length (L/d) = 5.9 outperformed the other configurations due to the low turbulence and entrainment. Finally, an Artificial Neural Network-based mathematical model is developed that correlates the ηlat as a function of flow and geometrical parameters.

Temperature analysis for the horizontal target cooling with non-confined and inclined air jet

In jet impingement cooling applications, the inclined jet in non-confined condition; also called as submerged jet is experimentally investigated. The objective is to analyze for hot surface cooling applications. Air is used as the working fluid, by using placement of jet on the leading edge of a horizontal rectangular target plate at height H, and examined for downhill side comprehensive cooling performance approach. The jet Reynolds number in the range of 2000 ≤ Re ≤ 20000 is investigated with circular jet for inclination of 15° ≤ θa ≤ 75°. The effect of jet to target distance (H) is also investigated in the range 0.5 ≤ H⁄D ≤ 6.8. The temperature variation at the center line of target is studied with analysis of temperature profile. Its variation with respective to horizontal distance of jet from leading edge (X) and counters are plotted for jet diameter (D) of 16mm. The location of minimum temperature during cooling by jet impingement, goes to downhill side for jet impingement with an angle of 75, 60, 45, 30 and 15°. Cooling is observed to be increase up to X⁄D = 5, and then it declines. The cold spot is seen at (X⁄D) of around 5 to 7 except at high Reynolds number. The impact of jet inclination is more on temperature variation of flat target, compared to other parameters.