Search

The macroscopic dynamics of a droplet impacting a solid is crucially determined by the intricate air dynamics occurring at the vanishingly small length scale between droplet and substrate prior to direct contact. Here we investigate the inverse problem, namely the role of air for the impact of a horizontal flat disk onto a liquid surface, and find an equally significant effect. Using an in-house experimental technique, we measure the free surface deflections just before impact, with a precision of a few micrometers. Whereas stagnation pressure pushes down the surface in the center, we observe a lift-up under the edge of the disk, which sets in at a later stage, and which we show to be consistent with a Kelvin-Helmholtz instability of the water-air interface., Comment: Supplementary text: "KHshort_shallowlayer.pdf". Movies: "deformingpattern.mp4" shows the deforming pattern from TIR images. "50mmprofile.mp4" and "80mmprofile.mp4" are videos showing reconstructed water surface profiles under the approaching disk

To investigate the combustion modes and unsteady characteristics during the condition transition of a scramjet combustor, a series of experiments were carried out under the condition of Mach 2.52 supersonic incoming flow, the corresponding stagnation pressure and temperature of which were 1.6 MPa and 1486 K, respectively. A fuel supply system that could dynamically adjust the injection pressure was adopted to simulate the condition transition stage of a scramjet. Based on the advanced combustion diagnosis technique, the transient chemiluminescence image and the wall pressure were recorded during the whole combustion process. Three typical modes of turbulent combustion occurred when the injection pressure drop gradually increased. The jet flame was stable after the condition transition when the injection pressure drop was relatively low. An unstable combustion phenomenon accompanied by intermittent local extinction and reignition could be found near the blowout limits. With a further increase in the injection pressure drop, the flame was blown out quickly during the transition process. In addition, the flame development characteristics during condition transition under stable combustion mode and the effect of injection pressure drop were studied in detail. During the process of switching between the two conditions, the area and light intensity of the flame decreased over time, and the wall pressure was accordingly reduced. As the increase in injection pressure dropped, the intensity of chemical reactions deceased obviously and the transition time became longer.

The distribution of wall static and stagnation (CP and CPO) pressure coefficient on a flat rectangular element by impinging air jet from the hexagonal orifice is obtained from experimentation. The past research studies helped to identify key parameters such as orifice geometry, jet exit-to-plate-distance (Z/dj), test section inclination (θ), jet Reynold number (Re), lateral distance-to-jet diameter (X/dj), test surface type and geometry, for better and acceptable results. The experimental outcome helps to know the effect of identified key parameters on wall static and stagnation pressure on a rectangular test plate in a confined flow path. The independent nature of wall static pressure is observed for all jet Reynold number (10000 ≤ Re ≤ 50000). Higher pressure coefficient values were observed at lower Z/dj = 1, X/dj = 0 and θ = 0. A significant drop in CP values are seen with the increase in Z/dj, X/dj and θ. The experimental CP and CPO contribution of confined flow are compared against the unconfined flow, around 48% to 58% enhancement is observed when confinement is used. Experimental pressure drop measurements across orifice were made and pressure loss coefficient (PC) for hexagonal orifice of confined and unconfined condition are reported.

The Hypersonic Materials Environmental Test System arc-jet facility located at the NASA Langley Research Center in Hampton, Virginia, is primarily used for the research, development, and evaluation of high-temperature thermal protection systems for hypersonic vehicles and reentry systems. In order to improve testing capabilities and knowledge of the test article environment, a detailed three-dimensional model of the arc-jet nozzle and free-jet portion of the flow field has been developed. The computational fluid dynamics model takes into account non-uniform inflow state profiles at the nozzle inlet as well as catalytic recombination efficiency effects at the probe surface. Results of the numerical simulations are compared to calibrated Pitot pressure and stagnation-point heat flux for three test conditions at low, medium, and high enthalpy. Comparing the results and test data indicates an effectively fully-catalytic copper surface on the heat flux probe of about 10% recombination efficiency and a 2-3 kPa pressure drop from the total pressure measured at the plenum section, prior to the nozzle. With these assumptions, the predictions are within the uncertainty of the stagnation pressure and heat flux measurements. The predicted velocity conditions at the nozzle exit were also compared and showed good agreement with radial and axial velocimetry data.

This work investigates the stagnation pressure gain in rotating detonation combustors (RDC) and its dependency on the geometry and mass flux of the combustor. Using a Kiel probe to directly measure stagnation pressure in the high-enthalpy exhaust stream, results are presented for a systematic variation of these parameters. The best-performing configuration achieved a pressure gain of −8%. A comparison with thrust-based equivalent available pressure data from literature shows that the Kiel probe measurements are in good agreement. It is observed that pressure gain increases with increasing air injector area, decreasing outlet throat area, increasing combustor mass flux, and is seen to be dependent on the operating mode. The data are then used to obtain an empirical model that describes pressure gain as a function of the three variables of injector area ratio, outlet area ratio, and combustor mass flux. The model is compared with measurements in this combustor and others, and is used to predict the pressure gain boundaries and to assess design corridors that potentially achieve positive pressure gain.

Article number 103720 We study numerically and experimentally the stability of the transonic flow focusing used in serial femtosecond crystallography (SFX) to place complex biochemical species into the beam focus. Both the numerical and experimental results indicate that the minimum flow rate for steady jetting increases slightly with the gas stagnation pressure. There is a remarkable agreement between the stability limit predicted by the global stability analysis and that obtained experimentally. Our simulations show that the steady jetting interruption at the critical flow rate is caused by the growth of a perturbation with a constant phase shift. This result is consistent with the experimental observations, which indicate that both the meniscus tip and the emitted jet collapse almost simultaneously at the stability limit. We derive a scaling law for the jet diameter as a function of the liquid flow rate and gas density/pressure from more than one hundred simulations. The scaling law provides accurate predictions for the jet diameter within the range of values [0.549,10.9] μm analyzed in this work. Ministerio de Ciencia e Innovación PID2019-108278RB Junta de Extremadura GR18175 Junta de Andalucía P18-FR-3623

An innovative design of a supersonic rotor pressure-exchange ejector is introduced in this paper. In this design, momentum is exchanged between supersonic primary flow and secondary flow using an idle rotor. A CFD code developed to model the 3-D compressible, viscous and turbulent flow of air inside the new design of ejector. Roe approach and Spallart-Allmaras methods used to analyze flow inside the ejector. The flow inside the ejector was modeled by using a structured grid and air was employed as the working fluid in both primary and secondary streams. The Mach number of the motive flow was set at 2. Momentum exchanged between the primary and secondary flows because of direct contact between those. In addition to that, rotation of idle rotor and mechanical blades entrained the secondary flow to the ejector. Enthalpy, entrained mass flow rate and created vacuum presented for the flow inside the ejector for different configurations of the rotor and ejector until an optimum case was achieved. Also, uniformity of the flow at discharge section compared between ejectors. For the optimum case with the presented geometry, the ultimate rotor speed of 50000 rpm was obtained and an increase of 47% in entrainment ratio achieved with respect to the stationary blades. To study the flow field in more details, the contours of the Mach number and stagnation pressure were compared according to the different sections of computational domain.

In the present study rotating vaneless diffusers are considered to minimize energy losses associated with diffusion and to improve the operating range of the compressor. Depending on the speed of rotation the diffusers are classified into two types forced and free. Simulations using ANSYS CFX 17.2 are performed with free rotating diffusers, in which diffusers are rotated at fraction of impeller speed. The performance of rotating diffuser with the stationary diffuser is compared using several performance characteristics such as total pressure ratio, static pressure recovery coefficient, coefficient of torque and stagnation pressure loss coefficient are plotted in each case. Simulations are performed at different speed ratio over a range of 0.25-0.95. Among all the cases vaneless diffuser with speed ratio 0.75 has optimum performance in terms of performance characteristics and velocity streamlines are uniform with lower Mach number compared to the stationary vaneless diffuser.

Previous in vitro studies have reported on the use of direct current electric fields (DC-EFs) to regulate vascular endothelial permeability, which is important for tissue regeneration and wound healing. However, these studies have primarily used static 2D culture models that lack the fluid mechanical forces associated with blood flow experienced by endothelial cells (ECs) in vivo. Hence, the effect of DC-EF on ECs under physiologically relevant fluid forces is yet to be systematically evaluated. Using a 3D microfluidic model of a bifurcating vessel, we report the role of DC-EF on regulating endothelial permeability when co-applied with physiologically relevant fluid forces that arise at the vessel bifurcation. The application of a 70 V m(−1) DC-EF simultaneously with 1 μL min(−1) low perfusion rate (generating 3.8 dyn cm(−2) stagnation pressure at the bifurcation point and 0.3 dyn cm(−2) laminar shear stress in the branched vessel) increased the endothelial permeability 7-fold compared to the static control condition (i.e., without flow and DC-EF). When the perfusion rate was increased to 10 μL min(−1) (generating 38 dyn cm(−2) stagnation pressure at the bifurcation point and 3 dyn cm(−2) laminar shear stress in the branched vessel) while maintaining the same electrical stimulation, a 4-fold increase in endothelial permeability compared to the static control was observed. The lower increase in endothelial permeability for the higher fluid forces but the same DC-EF suggests a competing role between fluid forces and the applied DC-EF. Moreover, the observed increase in endothelial permeability due to combined DC-EF and flow was transient and dependent on the Akt signalling pathway. Collectively, these findings provide significant new insights into how the endothelium serves as an electro-mechanical interface for regulating vessel permeability.

Sphingosine-1-phosphate (S1P) is a blood-borne bioactive lipid mediator of endothelial barrier function. Prior studies have implicated mechanical stimulation due to intravascular laminar shear stress in co-regulating S1P signaling in endothelial cells (ECs). Yet, vascular networks in vivo consist of vessel bifurcations, and this geometry produces hemodynamic forces that are distinct from laminar shear stress. However, the role of these forces at vessel bifurcations in regulating S1P-dependent endothelial barrier function is not known. In this study, we implemented a microfluidic platform that recapitulates the flow dynamics of vessel bifurcations with in situ quantification of the permeability of microvessel analogues. Co-application of S1P with impinging bifurcated fluid flow, which was characterized by approximately zero shear stress and 38 dyn cm-2 stagnation pressure at the vessel bifurcation point, promotes vessel stabilization. Similarly, co-treatment of carrier-free S1P with 3 dyn cm-2 laminar shear stress is also protective of endothelial barrier function. Moreover, it is shown that vessel stabilization due to laminar shear stress, but not bifurcated fluid flow, is dependent on S1P receptor 1 or 2 signaling. Collectively, these findings demonstrate the endothelium-protective function of fluid forces at vessel bifurcations and their involvement in coordinating S1P-dependent regulation of vessel permeability.

Scramjet engine is the most promising air breathing propulsion system in the hypersonic flight regime. Combustion in a scramjet engine, however, is difficult to achieve due to flow residence times being comparable to chemical times. For our study, 3-D RANS CFD analysis of a strut flame holder of a scramjet engine combustor was carried out. The first part of the analysis focuses on the validation of CFD gas dynamics results with earlier experimental data in literature. The air enters the combustor at Mach 2 with a stagnation temperature of 612 K and a stagnation pressure of 7.82 atm. Various flow properties like velocity profile, wall static pressure and density gradient were in good agreement with experimental results. The next part of the analysis involves a strut mounted across the walls of the combustor with hydrogen fuel injector jets forming an aerodynamic ramp on both the upper and lower surfaces. The location of the injectors relative to the strut base and dynamic pressure ratio were varied and the observations presented.

Surface pressure characteristics of elliptic cylinders of various thicknesses and orientations are investigated in steady flow regime. A stabilized finite-element method has been used to discretize the conservation equations of incompressible fluid flow in two dimensions. The Reynolds number, Re, is based on the major axis of cylinder and free-stream speed. Results have been presented for $$Re\le 40$$ and $$0^\circ \le \alpha \le 90^\circ $$ , where $$\alpha $$ is the angle of attack. Cylinder aspect ratios AR considered are 0.2 (thin), 0.5 and 0.8 (thick). It is found that a decrease in AR does not significantly alter the location of minimum surface pressure for $$\alpha = 90^\circ $$ , but the value of minimum pressure decreases sharply, resulting in severe adverse pressure gradient. In contrast, for $$\alpha = 0^\circ $$ , the location travels towards the base and the minimum pressure increases, leading to delayed flow separation. In general, the magnitude of forward stagnation pressure at low Re is smaller than the maximum pressure for $$AR\le 0.5$$ . The maximum pressure occurs at the forward stagnation point as the Re and AR increase. However, in most cases, the locations of forward stagnation and maximum pressure points differ even when the pressure coefficients are very close to each other. The forward stagnation and maximum pressure coefficients of an elliptic cylinder decrease monotonically with increasing $$\alpha $$ . The drag of a circular cylinder in most cases exceeds the ones obtained for elliptic cylinders. With increasing AR, the drag increases approximately linearly for small $$\alpha $$ , lift decreases approximately linearly and moment decreases non-linearly. For a thick cylinder, while the effect of Re on lift and moment is insignificant, the drag shows a strong dependence. Roughly $$\alpha = 20^\circ $$ for $$Re = 40$$ flow represents a critical angle of attack below which a cylinder of $$AR\le 0.5$$ acts like a streamlined body and above, like a bluff body.

In this study, a computational investigation of multiphase flow within supersonic micronozzles has been performed in an effort to quantify the impact on thrust production and nozzle efficiency. Mot...

An effective fuel supply strategy with high mixing efficiency, large penetration depth and low stagnation pressure losses determines the overall performance of the scramjet (supersonic combustion ramjet) engine. In this paper, the transverse hydrogen injection flow field with a micro-ramp located upstream of the wall orifice has been investigated numerically based on the code validation. There are four design variables considered in the current study, namely the width, length, and height of the micro-ramp and the distance between the center of the wall orifice and the trailing point of the micro-ramp. Nine cases predicted by the three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations coupled with the two equation k–ω shear stress transport (SST) turbulence model are used for parametric analysis, and the parametric analysis has been carried out by the extreme difference analysis approach. Three optimization cases are obtained, and they have different objectives, namely the minimization of the mixing length, the maximization of the penetration depth and the minimization of the stagnation pressure losses. The flow structures of all cases have been discussed and compared. The quantitative evaluation results of three optimization cases show that the extreme difference analysis approach is an efficient parametric analysis method, and it can obtain the optimal strategy for the micro-ramp within scramjet combustors with the transverse hydrogen jet.

The article presents the results from putting a new automated flow traversing measurement system (AFTMS) in an experimental turbine intended for testing steam paths of the low-pressure cylinders (LPC) of large-capacity steam turbines into use. Modern computerized facilities have been used in developing the system. Such an approach has been implemented for the first time in the full-scale test bench available at PJSC Power Machines in carrying out experimental investigations of an LPC double stage compartment (on a 1 : 1 scale) equipped with a new, ultimately long last stage blade (LSB) developed for a steam turbine plant for ultrasupercritical steam conditions. The investigations were aimed at confirming the effectiveness of the developed system in measuring the flow parameters in the last LPC stage. The necessity of making a shift from nonautomated and semiautomatic systems to the use of automated measurement systems is substantiated. The article describes a system that makes it possible, with automated setting of the gas dynamic probe head position on the traversing line, to determine the steam flow direction; to measure the stagnation pressure, static pressure, and stagnation temperature; and to record the measures indicators with exactly assigned time tags. The results from measurements of flow parameters upstream of the last LPC stage in a partial load mode are given. A comparison between the experimental and calculated flow parameter distribution data over the stage radius in the control section is shown.

The propulsive performance for an H2/O2 and H2/Air rotating detonation engine (RDE) with conic aerospike nozzle has been estimated using three-dimensional numerical simulation with detailed chemical reaction model. The present paper provides the evaluation of the specific impulse (Isp), pressure gain and the thrust coefficient for different micro-nozzle stagnation pressures and for two configurations of conic aerospike nozzle, open and choked aerospike. The simulations show that regardless of the nozzle, increase the micro-nozzles stagnation pressure increases the mass flow rate, the pre-detonation gases pressure and consequently the post-detonation pressure. This gain of pressure in the combustion chamber leads to a higher pressure thrust through the nozzle, improving the Isp. It was also found that the choked nozzle increases the chamber time-averaged static pressure by 50–60% compared with the open nozzle, inducing higher performance for the same reason explained before.

We use interface-resolved direct numerical simulations to study the dynamics of a single sediment particle in a turbulent open channel flow over a fixed porous bed. The relative strength of the gravitational acceleration, quantified by the Galileo number, is varied so as to reproduce the different modes of sediment transport – resuspension, saltation and rolling. The results show that the sediment dynamics at lower Galileo numbers (i.e. resuspension and saltation) are mainly governed by the mean flow. Here, the regime of motion can be predicted by the ratio between the gravity and the shear-induced boundary force. In these cases, the sediment particle rapidly takes off when exposed to the flow, and proceeds with an oscillatory motion. Increasing the Galileo number, the frequency of these oscillations increases and their amplitude decreases, until the transport mode switches from resuspension to saltation. In this case, the sediment travels by short successive collisions with the bed. Further increasing the Galileo number, the particle rolls without detaching from the bed. Differently from the previous modes, the motion is triggered by extreme turbulent events, and the particle response depends on the specific initial conditions, at fixed Reynolds number. The results reveal that close to the onset of sediment motion, only turbulent sweeps can effectively trigger the particle motion by increasing the stagnation pressure upstream. We show that for the parameters in this study, a criterion based on the streamwise flow-induced force can successfully predict the incipient movement.

This work is focused on the experimental characterization of shock-dominated flow structures, parameters, and dynamics under control by a filamentary plasma array. Testing was performed in the supersonic blowdown test rig SBR-50 at the University of Notre Dame at flow Mach number M = 2 and stagnation pressure P0 = 1.7 bar. A shock wave (SW) generator composed of a symmetric 10° wedge was installed on the top wall of a 710 mm long test section. The filamentary plasma array based on a Q-DC discharge was arranged on the opposite wall so that the main SW originating from the wedge impinged the plasma area. As a result of the SW-plasma interaction the flowfield was significantly modified over the test section, including an upstream shift of the main SW and pressure redistribution. Basic instrumentation included fast schlieren visualization, wall pressure measurements and Pitot-rake measurements at the end of the test section. Additionally, a fast Pressure Sensitive Paint (PSP) technique was employed to acquire details of the SW footprint and capture transitional effects after switching plasma off and on. Analysis of the data acquired by these complementary methods allowed for reconstruction of a three-dimensional portrait of shock-dominated flow interaction with the plasma zone. The mechanism of SW-plasma interaction and the plasma effect on total pressure losses in the duct are also discussed.

The detailed evolution process of deuterium and hydrogen supersonic molecular beam (SMB) was probed by one simple method based on the microphone. The velocity of the beam was measured by time-of-flight method, and the density was investigated by comparing the radial profiles of the SMB with the total amounts of molecules in the gas jet. The velocity and number density of deuterium SMB generated from a cylindrical nozzle were tested to be 1100 m/s and 3.6E15 cm−3 at axial distance of 1700 mm and stagnation pressure of 50 bar, which was about 30% lower than that of hydrogen SMB generated from the same nozzle, and was in consistent with the total number of molecules in deuterium gas jet that was 30% smaller than hydrogen. It is found that the use of a cylindrical nozzle and arrangement of a special skimmer can increase the central density of SMB by about 150% and 45%, while the utilization of one conical nozzle would increase the velocity of the SMB by 13%, these results could give great help in the SMB diagnostics and fueling of the nuclear fusion experiments.

Ejectors invariably convert momentum and kinetic energy of incoming fluids into enthalpy and hence pressure. Since ejectors are primarily viewed as energy exchange devices, it would be appropriate to design an ejector with its geometry being a function of the rate of energy change. This would shift ejector design approach from conventional geometry based one to that of flow physics-based approach. Hence, the paper presents a unique approach to evolving ejector design considering it primarily to be a function energy change within the system, specifically being constant rate of kinetic energy change (CRKEC). This approach has benefits in terms of mitigating the occurrence of thermodynamic shock, which is a major irreversibility that besets conventional ejector systems. A 1-D gas dynamic model including frictional effects for a more realistic design has been developed for estimating supersonic ejector geometry based on CRKEC approach. The model has been used to predict the geometry of a supersonic air ejector for typical input parameters viz., entrainment ratio (ω) ∼0.53, recovery ratio(ζ) ∼1.4, primary stagnation pressure(Pop) ∼5.7 bar, secondary stagnation pressure(Pos) ∼0.7 bar. The results have been verified through detailed numerical analysis using Navier-Stokes system of equations with turbulence in a 2-D axi-symmetric formulation. Also, the experimental results on the developed prototype, which have also been discussed, are observed to be in close agreement with predictions of 1-D gas dynamic model and the numerical studies.

Reliable and fast ignition of scramjet engine is quite important in consideration of high velocity and low pressure of inlet air. Successful ignition requires that sufficient ignition energy be injected into the flame kernel so that the flame propagates outwardly beyond the critical initial radius of the critical flame. Larger critical flame initiation radius is required during the preliminary stage of scramjet engine so advanced ignition technology for scramjet engines is urgently needed. In this study, multichannel plasma igniter (MCPI) is proposed to induce a relatively larger ignition kernel for the purpose of achieving successful ignition in scramjet engines. Ignition experiments in a model scramjet combustor fueled by ethylene were conducted with inflow conditions of Ma = 2.52, stagnation pressure P 0 = 1.6 MPa and stagnation temperature T 0 = 1600 K. Ignition processes of SI and MCPI at different fuel injection schemes were captured by CH∗ chemiluminescence imaging and flame luminosity imaging technology. Results reveal that MCPI with five channels generates 5 times more ignition energy than SI and MCPI can generate much larger plasma volume and activated area which can induce a relatively larger initial flame kernel. The CH intensity of MCPI was about 2.2 times larger than that of conventional SI. Besides, it was shown that the lean ignition limit of scramjet combustor through MCPI was extended by 20–26% than that through SI and the ignition time was reduced by approximately 50%. MCPI with an injection 10 mm upstream the cavity demonstrates the best performance in this study.

This paper focuses on the problem of the modeling of the supersonic ejector under both critical and subcritical mode. Unlike the traditional 1D mathematical model, the proposed model takes into account the non-uniform distribution of the flow field in the radial direction. For the critical point, it is assumed that the mixing progress occurs in the constant area mixing chamber under a uniform mixing pressure which is between the stagnation pressure and choking pressure of the secondary flow. However, a constant area mixing assumption is made when the ejector operates under the subcritical mode. By using an exponential relationship to approximate the velocity distribution of the secondary flow in the radial direction, both the entrainment ratio and back pressure can be calculated. The influence of component efficiencies on the ejector performance for different working fluids is presented and analyzed. Finally, experimental results are used to validate the effectiveness of the proposed model.

A simple physics-based model was developed for the prediction of shock-train location in constant-area scramjet isolators. The shock train was shown to manifest at the location within the isolator ...

As one of the most promising propulsion systems in the future, there are unusual advantages of the shock-induced combustion ramjet (shcramjet) engine. In the current study, the slot is placed on the second ramp of the shcramjet inlet to promote the mixing process between the fuel and the hypersonic crossflow. The influences of the injection angle and the jet-to-crossflow pressure ratio have been investigated numerically based on the grid independency analysis and the code validation. The obtained results predicted by the two-dimensional Reynolds-average Navier-Stokes (RANS) equations coupled with the two equation RNG k-e turbulence model show that the grid scale makes only a slight difference to the wall pressure profiles for all jet-to-crossflow pressure ratios employed in this article. With the smaller injection angle, higher fuel/air mixing efficiency, less loss of the stagnation pressure and lower fuel penetration depth are shown. Low jet-to-crossflow pressure ratio can increase the mixing efficiency and decrease the loss of the stagnation pressure. High jet-to-crossflow pressure ratio results in higher penetration depth. There is an optimum injection angle for each jet-to-crossflow pressure ratio to achieve the maximization of the fuel/air mixing in hypersonic flows.

This paper proposes a new methodology for physics-based aircraft multidisciplinary design optimization (MDO) and sensitivity analysis. The proposed architecture uses signomial programming (SP), a t...

A numerical investigation has been conducted for the drag reduction of a counterflow jet with a blunt body at Mach 6. The computational study was carried out by solving two-dimensional axisymmetric Reynolds-averaged Navier–Stokes (RANS) equations. The Spalart–Allmaras one-equation turbulence model was used in this study. The jet flow of exit Mach number 2.86 interacts with the free stream and changes the single shock structure to a multiple shock structure. The purpose of this study was to investigate the influence of the stagnation pressure based on a parameter, the momentum parameter ratio (MPR), which can characterize the jet. The result shows that the flow field can be categorized as being in a long penetration mode (LPM) or short penetration mode (SPM) depending on the penetration length of the free-stream flow. In the LPM, under overexpanded jet conditions, the shock structure fluctuates continuously, so the flow field is unstable. On the other hand, in the SPM, the shock structure is nearly fixed, and the entire flow field is stable. For this reason, even if the penetration length of the flow field in the SPM is less than that in the LPM, the aerodynamic drag can be reduced by up to 40%. Therefore, it becomes clear that jet pressure conditions can significantly improve aerodynamic performance by reducing the drag applied to the blunt body.

A low area ratio rectangular supersonic gaseous ejector is subjected to parametric evaluation to calculate the performance parameters like stagnation pressure ratio, compression ratio, entrainment ratio and the mixing parameter known as non-mixed length for a wide range of operating conditions by varying the secondary flow rate. The operating conditions are achieved by varying the design Mach number of the primary flow nozzle, the total pressure of the primary flow and the secondary flow rate. Air is used as the working fluid in both the primary and secondary flow. The ejector is operated in the mixed regime. Mach number ratio is used as the non-dimensionalization parameter, and fully-expanded jet height is used as the scaling variable to collapse the huge set of obtained data for parametric studies. With variation in the secondary flow rate, staging is observed in the compression ratio, entrainment ratio, and also in the non-mixed length. Variation in the entrainment ratio and non-mixed length are observed to be linear, and it scales well with the fully-expanded jet height when there is a deficit in the secondary flow. Also, when there is no secondary flow, the non-mixed length is observed to be 80% lower in comparison with the case, where the secondary flow is uncontrolled. Schlieren visualization and wall static pressure measurements supplement the findings.

A needle-free injection system is a non-invasive drug delivery system, and its applications are currently being extended from the delivery of vaccines and insulin. At present, they are gaining considerable popularity in skin remodeling treatment techniques, particularly in skin rejuvenation procedures involving the injection of aesthetic materials. Although some clinical studies have been conducted to understand the mechanisms involved in these practices, an extensive study from an engineering point of view has not yet been conducted. Herein, we aim to identify the key parameters in the needle-free injection process and study their effects on microjet characteristics. The total stagnation pressure of an impinging microjet determines the penetration capabilities of the injection and is monitored with the aid of both experimental and computational tools employed on a typical commercial injector. Our findings indicated that the filling ratio and driving pressure had significant impacts on the peak and average stagnation pressures of the impinging microjet. Furthermore, the penetration characteristics of a standard nozzle and injection fluid could be controlled by an effective combination of the filling level and driving pressure, and thus, they can be considered as vital parameters when performing skin remodeling procedures.

Condensation in the primary nozzle of a steam ejector changes the steam jet properties during the nozzle expansion process and affects the mixing rate of the primary and secondary streams and thus the performance of steam ejectors. Only limited experimental data is available for the mixing of wet steam jets at conditions relevant to steam ejectors. The present work provides static and pitot pressure measurements within a wet supersonic steam jet which mixes with a low pressure co-flowing secondary stream. High pressure steam was delivered to the primary nozzle at a stagnation pressure and temperature of 270 kPa and 406 K, respectively. The primary nozzle throat diameter was 3.2 mm and its exit diameter was 13.6 mm. Pitot and static pressure measurements were obtained on the mixing jet centreline from the nozzle exit to a downstream location of 185 mm in the mixing chamber. Radial profiles of pitot and static pressure were also measured at positions of 5, 20, 35, 85, 135 and 185 mm downstream of the nozzle exit. With the mixing chamber pressure maintained at approximately 1.3 kPa, the mixing jet was in an under-expanded condition. CFD simulations with a non-equilibrium wet steam model also demonstrate the under-expanded jet structure. The pitot pressure profiles at the furthest locations downstream (135 and 185 mm) show reasonable agreement between experiments and simulations in terms of the spreading of the jet due to turbulent mixing. However, there are significant differences between the experimental and simulated pitot and static pressures profiles in the transverse and axial directions. Contributions to these differences are likely to arise because the simulated static pressures in the under-expanded wet steam jet core are lower than the triple point for water (0.61 kPa), so potential exists for liquid-solid and vapour-solid phase transitions that are not currently modelled in the simulations.

A new injection strategy combined with a micro-ramp and an air porthole is proposed in this paper, and the properties of the transverse gaseous injection flow field with such injection strategy have been investigated simultaneously. The numerical approach employed in the current study has been validated against the two-dimensional and three-dimensional experimental data in the open literature, and it can be used with confidence to investigate the influence of the air porthole aspect ratio and the distance between the air porthole and the fuel orifice on the transverse injection flow field with the combination of a micro-ramp and an air porthole. The obtained results predicted by the three-dimensional Reynolds-average Navier–Stokes (RANS) equations coupled with the two equation k-ω shear stress transport (SST) turbulence model show that the mixing performances of the transverse gaseous injection flow fields vary under different conditions, and a transverse injection flow field with short mixing length, low stagnation pressure loss and ideal fuel penetration depth has been achieved by adding the combination of an optimized micro-ramp with a proper air porthole, i.e. Case 6–8, and its mixing length decreases considerably by 14.26 mm on the basis of Case c, even shorter than the mixing length of Case a by 2.86 mm. However, its total pressure loss increases when compared with Case c, and its stagnation pressure loss is 2.7 percent smaller than Case a. Further, the hydrogen distribution on the flat plate of Case 6–8 is much less than that of Case a and Case b. Additionally, it is found that the mixing enhancement mechanism of the air jet is different from that of the micro-ramp. The micro-ramp enhances the mixing process between the fuel and air by inducing large-scale vortices, while the air porthole enhances the mixing process by seeding lots of air into the fuel boundary layer, as well as fuel plume.

Experiments on heat transfer in supersonic underexpanded high-enthalpy air jets are conducted on the VGU-4 induction plasmatron at the pressure in the compression chamber of 8.5 hPa. At the air flow rate of 3.6 g/s and the high-frequency generator powers of 45 kW(regime 1) and 64 kW (regime 2) the heat fluxes to the copper surface at the stagnation point of watercooled cylindrical models along the axes of dissociated air jets are measured. The models, 30 mm in diameter, could have a flat face or a hemispherical nose. In the same regimes, the stagnation pressures are measured using the Pitot tube in the shape of a cylinder, 30 mm in diameter, having either a flat face or a hemispherical bluntness with a receiving hole, 14 mm in diameter. For the experimental conditions calculations of flows in the plasmatron discharge channel and supersonic underexpanded jets issuing from the discharge channel are performed within the framework of the Navier–Stokes and Maxwell equations. The heat fluxes to the experimental models are computed and compared with the experimental data.

A numerical study has been conducted to analyze boundary effects, including different inlet boundary conditions and different inlet section lengths (distances from the inlet boundary to the heated section), on flow dynamics in transient supercritical-pressure heat transfer of n-decane in a circular tube. As the inlet boundary condition changes from a constant flow velocity to a constant stagnation pressure, the pressure oscillation frequency is nearly doubled, and the thermoacoustic wave is in the first longitudinal mode. The frequency of mass flow rate oscillation is essentially the same as that of the pressure wave. Different inlet boundary conditions exert no effect on the pressure wave amplitude but make strong influence on the amplitude of mass flow rate oscillation at the outlet of the heated section. As the inlet insulation section length increases under a constant inlet stagnation pressure, frequencies of both pressure and mass flow rate oscillations proportionally decrease, and the thermoacoustic waves remain in the first longitudinal mode. Different inlet section lengths appear to make only minor effect on the amplitudes of both pressure and mass flow rate oscillations at the outlet of the heated section, and the maximum amplitude in each wave is around 10% of its steady-state value.

International audience; Since the beginning of civil aviation, icing is a severe weather hazard for aircraft operation. In this context, the phenomenon of ice crystal icing has been identified as a risk for flight safety in the recent past. Ice crystals can accrete on warm components such as heated stagnation pressure probes and engine compressor blades. Liquid melt water or additional liquid droplets in the icing cloud enable the ice particles to stick to the component surface and to form a cohesive ice accretion layer. In this paper, we present results of comprehensive icing wind tunnel tests on ice crystal ice accretion together with results of complementary simulations by means of the ONERA icing code IGLOO2D. The experiments show a strong influence of ambient temperature on the icing process. In agreement with literature findings, ice particle sticking ability can be correlated with the ice cloud composition. Correlations between accretion shape and growth rate have been identified. IGLOO2D separates accretion abrasion by particle impact from the efficiency with which those particles stick to the deposit. Comparisons of computational and experimental results indicate that this sticking efficiency has the greatest effect on ice shapes at low Mach numbers, at least for the particle sizes and conditions used in the experiments. The experimental and numerical findings of this study can be considered as complementary to existing knowledge on ice crystal icing. Therefore, the experimental results are provided to an international benchmark of test cases for icing code validation.

Silicon nitride ceramics were prepared by means of a hot-press sintering method. The ablation behavior was studied by plasma wind tunnel tests. The data suggested that, under low heat flux and stagnation pressure conditions, the ablation process was controlled by the atomic oxidation of Si3N4, leading to the elimination of Si3N4. By contrast, the erosion was mainly produced by the decomposition of Si3N4 under high heat flux and stagnation pressure conditions. Under these conditions, a fraction of Si phase, formed upon decomposition of Si3N4, was volatilized. The remained Si had melted due to high temperatures and scoured away from stagnation point area, generating mushroom-shaped samples.

The wavy cylinders have been proven effective in suppressing the Karman vortex shedding and mitigating the aerodynamic forces. As yet their performance in the inclined incoming flow has not been well understood. In the current work, large eddy simulations are carried out to unveil the aerodynamics of the flow around inclined wavy cylinders at the Reynolds number of 5000. Three inclination angles, 0 ° , 30 ° and 45 ° , together with 2 × 2 combinations of shape parameters, namely λ ∕ D m = 2 and 6, a ∕ D m = 0 . 1 and 0.15, have been taken into consideration. Firstly, the aerodynamic force coefficients in terms of both the span-wise averaged and sectional values are discussed at length. It is revealed that the growing inclination angle invites not only a surge in their span-wise averaged values, but also an enlargement in the sectional difference of the force coefficients. The span-wise correlation of the lift force is found to be enhanced for the wavy cylinders with the increase of inclination angle, while the opposite is true for the normal cylinders. By examining the mean wake properties, it is disclosed that the increase in the span-wise averaged drag force coefficients is closely related to the shrinkage in the vortex formation length and the regression of the base pressure, whereas the sectional distribution of the drag coefficients is largely affected by the stagnation pressure. The mean wall shear stress fields are exploited to shed light on the flow topology of the cylinder surfaces. It is discovered that the wavy cylinders, especially the short-wavelength one, exhibit significant span-wise variation in the separation structure in the inclined flow. Besides, the chaotic surface flow in the rear side of the non-inclined cylinders could be regulated to maintain symmetry by the secondary axial flow in the near wake of the inclined cylinders. The instantaneous three-dimensional vortical structures are visualized by the Q isosurfaces at last to collaborate the previous discussions. A preliminary mechanism for the cessation of flow control efficacy for the wavy cylinders in inclined flow is also presented.