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Regular inspections and hull cleanings are essential to prevent bio-fouling on ships. However, traditional cleaning methods such as brush cleaning and high-pressure water-jet cleaning at docks are ineffective in cleaning niche areas like bow thrusters and sea chests. Consequently, cleaning robots based on brushes and water jets have been developed to effectively remove bio-fouling. However, there are concerns that brushes may damage hull coatings, allowing bio-fouling to penetrate the damaged areas. In this study, removal experiments were conducted to identify the most dominant factor in fouling removal using water jet-based cleaning, in preparation for the development of non-contact cavitation high-pressure water jet-cleaning robots. The Taguchi method was used to identify influential factors and generate experimental conditions, and equipment systems for the removal experiments were established. Image analysis was performed to assess the bio-fouling occurrences on each specimen before and after cleaning, and numerical simulations of the nozzle were conducted to estimate stagnation pressure and wall shear stress to confirm the effect on micro-fouling removal. The results indicated that pump pressure is the most influential factor in removing large bio-fouling organisms grown in marine environments and on ship surfaces. [ABSTRACT FROM AUTHOR]

Stagnation pressure is usually increased by so-called machine methods—various compressors that operate by supplying mechanical energy to the flow. This paper considers a method for increasing the stagnation pressure based on the thermal influence on the flow (heat removal). The influence of various factors on the degree of the increase in stagnation pressure for a channel flow under only thermal influence is studied. This paper considers various flow cooling methods. It is shown that evaporative cooling is the most effective in terms of increasing the stagnation pressure. A review of publications on the use of evaporative cooling to increase stagnation pressure is provided. Based on a one-dimensional model of an evaporative cooling device, it is shown that it is possible to increase stagnation pressure by a factor of 1.25 at supersonic inlet velocities. [ABSTRACT FROM AUTHOR]

Needle-free jet injectors are minimally invasive drug delivery systems that utilise high-velocity microjets (~100 m/s) created by pressurising the liquid drug through a micronozzle (50-300µm in diameter). Most of the current commercially available jet injectors use a mechanical power possessed by a compressed spring or air to pressurise the fluid inside the injection chamber to deliver the liquid drug (typically ~100 µL in volume) into the skin matrix. However, they cannot be utilised for achieving shallow penetration depths as they lack dynamic control that can shape the real-time microjet characteristics. Recently, electrically or optically powered jet injection systems are being developed to achieve shallow penetration depth by small-volume (<5μL) injections. However, they require complex system and have a limited injection frequency (maximum reported value is 16 Hz). Herein, we propose a novel electro-mechanical jet injection system, where a mechanically actuated source pressurises the fluid inside the injection chamber and an electrically actuated system controls the characteristics of the propelled microjet. A computational model was developed to prove the feasibility of the proposed system, and the obtained results showed that the proposed system could produce stable small-volume microjets at about 100 Hz frequency that could be utilised for drug delivery applications. [ABSTRACT FROM AUTHOR]

Regular inspections and hull cleanings are essential to prevent bio-fouling on ships. However, traditional cleaning methods such as brush cleaning and high-pressure water-jet cleaning at docks are ineffective in cleaning niche areas like bow thrusters and sea chests. Consequently, cleaning robots based on brushes and water jets have been developed to effectively remove bio-fouling. However, there are concerns that brushes may damage hull coatings, allowing bio-fouling to penetrate the damaged areas. In this study, removal experiments were conducted to identify the most dominant factor in fouling removal using water jet-based cleaning, in preparation for the development of non-contact cavitation high-pressure water jet-cleaning robots. The Taguchi method was used to identify influential factors and generate experimental conditions, and equipment systems for the removal experiments were established. Image analysis was performed to assess the bio-fouling occurrences on each specimen before and after cleaning, and numerical simulations of the nozzle were conducted to estimate stagnation pressure and wall shear stress to confirm the effect on micro-fouling removal. The results indicated that pump pressure is the most influential factor in removing large bio-fouling organisms grown in marine environments and on ship surfaces.

The HLLC scheme is an accurate, approximate Riemann solver. However, it suffers from the carbuncle phenomenon and numerical shock instability problems on both rectangular and triangular grids. In this paper, a hybrid HLLC scheme (HLLC+) is developed by adding some extra computations to the original HLLC scheme in order to achieve a stable and accurate scheme. The idea of the hybrid scheme is straightforward as it uses a simple shock-capturing function with parameter κ to detect regions where pressure oscillations such as shock waves are significant. In these regions, a less diffusive version of the AUSMV+ scheme (AUSMV2+) is activated with a new weighting function with parameter κ. This new weighting function is designed to control the stability and accuracy of the hybrid scheme via the ratio of the square of the speed of sound of two adjacent cells. A linear perturbation analysis of an odd-even decoupling problem is used to analyze the effectiveness of the proposed hybrid scheme in damping perturbations. Several numerical examples are given to demonstrate that the new scheme (HLLC+) can obtain accurate solutions and that it is simple and efficient and requires comparable computational time with the original scheme. [ABSTRACT FROM AUTHOR]

In the present work for a quasi-one-dimensional isentropic compressible flow model, an empirical equation of the Mach number is constructed as a function of the stagnation pressure ratio for an analytical equation that algebraic procedures cannot invert. The Excel 2019 Solver tool was applied to calibrate the coefficients and exponents of the empirical equation during its construction for the Mach number range from 1 to 10 and 1 to 5. A specific heat ratio from 1.1 to 1.67 and the generalized reduced gradient iterative method were used to minimize the sum of squared error, which was set as the objective function. The results show that for Mach 1 to 10, an error of less than 0.063% is obtained, and for Mach 1 to 5, an error of less than 0.00988% is obtained. It is concluded that the empirical equation obtained is a mathematical model that reproduces the trajectories of the inverted curves of the analytical equation studied.

Controlled, guided munitions can reduce dispersion in the shot, while providing the capability of engaging both stationary and maneuvering targets. The Netherlands Organisation for Applied Scientific Research has developed a fin-less control technology called Stagnation Pressure Reaction Control (SPRC) that takes stagnation pressure air and directs it sideways to control non-spinning projectiles. In a previous study, this technology was demonstrated at Mach 2 wind-tunnel conditions to achieve up to 1.5° controllable angle of incidence for a non-spinning, aerodynamically unstable projectile-like test object. In an operational scenario, the decelerating projectile will experience a decline in control force while the simultaneous forward shift of the center of pressure increases the need for control force. Furthermore, angles of incidence exceeding 1.5° will be experienced under realistic flight conditions, especially against maneuvering targets. This work addresses these challenges and presents an operational feasibility study for a practical application of SPRC in a non-spinning mid-caliber gun-launched projectile, using experiment data on control latency and force of the earlier study. It illustrates the combined effect of the control- and stability dynamics and underlines the potential of an SPRC projectile as a precisionoperation ammunition. This research revealed that SPRC technology can stabilize and control the hypothesized projectile in a direct fire scenario against stationary and maneuvering targets. [ABSTRACT FROM AUTHOR]

This work experimentally studied combustion oscillations in a cavity-based combustor operating under high-enthalpy supersonic flow. Three fuel-injection distances and the corresponding combined fuel injection schemes were tested and compared with the global equivalence ratio unchanged. The results indicate that the combustions of longer and medium distances (35 and 21 mm, respectively) present stronger oscillations, which are mainly attributed to the strengthened oscillations of the mainstream flame (MF). It is also found that combined fueling schemes can help weaken the oscillations. The predominant frequencies of the combustion oscillations in different fueling schemes are all distributed at approximately 400 Hz, which are proven to be induced by the MF. The low-frequency range (0-50 Hz) is more dominant for the shorter injection distance (7 mm) than in the other cases, which is because the flames are strongly influenced by low-frequency disturbances with fluctuations in the fueling injection and inflow. The analysis reveals that these disturbances act primarily on the cavity flame. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of Nanjing University of Aeronautics & Astronautics is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Focused laser differential interferometry (FLDI) is used to make freestream density fluctuation measurements in the von Kármán Gas Dynamics Facility (VKF) Wind Tunnel D at Arnold Engineering Development Complex. A comparison is made between pitot-probe and FLDI measurements after converting both to freestream pressure fluctuation spectra. A modification of Stainback and Wagner's theory, incorporating recent numerical results from Chaudhry et al., is used to interpret the pitot data, while a new inversion algorithm is applied to the FLDI data. These methods of interpretation make the assumption that the tunnel freestream disturbance environment is dominated by the acoustic Kovásznay mode, in line with the theoretical and experimental evidence. Close agreement is found between the two sets of spectra, showing that accurate quantitative data can be obtained with FLDI, and the instrument can be used to extend spectra beyond the pitot bandwidth. [ABSTRACT FROM AUTHOR]

The needle-free injection is a new technique for treating subcutaneous drug delivery through penetrating the skin with a high-speed liquid drug jet. The present study aims to reveal fluid dynamics characteristics of the needle-free injection. The operational parameters such as the driving pressure, the nozzle diameter and the liquid volume were investigated for an air-powered needle-free injection system using experimental techniques. The results show that the peak stagnation pressure determines the penetration performance of the jet and is significantly affected by the driving pressure, nozzle diameter and liquid volume. Furthermore, the entire injection process of fluid in the gel can be defined as two phases of penetration and diffusion. Thus, the dispersion characteristics of fluid in different phases could be controlled by an effective combination of the nozzle diameter and liquid volume. Overall, the obtained conclusions provide a sound support for understanding the operation of the needle-free injector. [ABSTRACT FROM AUTHOR]

Kiel probes have the potential to be a versatile tool for determining stagnation pressure gain in rotating detonation combustors (RDCs), accompanying the commonly used equivalent available pressure method. Although average pressure gain values determined with Kiel probes are comparable to those from thrust stand experiments, one can expect several sources of measurement error from the unsteady trans- and supersonic environment. This work investigates the response of a Kiel probe in highly unsteady flow, similar to what would be encountered in an RDC. The probe is subjected to an underexpanded starting jet behind an incident shock with Mach numbers of 1.6-2.7, emanating from a shock tube with a reservoir ratio of about 394. The incidence angle of the probe is varied between 0 and 90 deg, as is the probe's axial location with respect to the tube's exit plane. High-speed schlieren images reveal the Mach number of the moving shock wave and the structure of the detached bow shock at the Kiel head, which is similar to that of a bluff body. It is shown that the measured stagnation pressure signal is independent of inflow angle over a range of ±45 deg, and that signal attenuation is caused by gas processing through the bow shock and viscous losses in the probe's capillary. The frequency response of the Kiel probe to sinusoidal, small-amplitude pressure fluctuations is determined in an acoustic calibration facility up to 5500 Hz, confirming linear behavior and that no unwanted resonance is present in the probe. A Berg-Tijdeman representation delivers amplitude ratio and phase lag of comparable magnitude. An assessment of representative boundary conditions reveals that the average stagnation pressure measurement error is of the order of 1%. [ABSTRACT FROM AUTHOR]

Flow unsteadiness in supersonic impinging jets due to the aeroacoustic feedback can lead to practical problems like ground erosion in short takeoff and vertical landing aircraft, high noise levels, and high unsteady structural loading. The shear-layer instabilities of the jet play an important role in the flow dynamics. A full study of these instabilities requires time-resolved measurements of the flow velocity field. However, experimentally obtaining time-resolved velocity fields, derived from particle image velocimetry (PIV) techniques, has its challenges in high-speed flow applications due to the simultaneous requirement of high spatial and temporal resolution. A novel approach is presented in this paper, which uses time-unresolved dual-time digital PIV coupled with dynamic mode decomposition (DMD) analysis (DT-DPIV-DMD) of the velocity field pairs and applies it to study the dynamics of the shear-layer instabilities in supersonic impinging jets. DT-DPIV-DMD involves the acquisition of a pair of instantaneous velocity fields separated by a small time delay using two covisual PIV systems. The time delay must be sufficiently small to provide the necessary bandwidth to capture all the relevant dynamics of the flow being investigated. This is followed by DMD analysis of all acquired digital PIV velocity field pairs. A large-eddy simulation of an underexpanded impinging jet at Reynolds number 60,000, with nozzle-to-wall distance h/d=5 was first used to investigate the required measurement scales for the application of DT-DPIV-DMD. Using the optimum measurement scales, the technique was then experimentally demonstrated using DT-DPIV-DMD for two supersonic impinging jets cases and validated with acoustic measurements. [ABSTRACT FROM AUTHOR]

Coupled aerothermoelastic simulations are required for the accurate simulation of many high-speed flow problems. Hence, the multidisciplinary analysis of such problems is the main focus of the current work. In this study, flow simulations are carried out using a three-dimensional implicit finite volume computational fluid dynamics solver developed in house that has been well tested and validated through numerous previous studies. For the thermal and structural solutions, a finite element solver is used, which is also developed and validated in house. The coupled aerothermoelastic platform is validated in this work through two applications. In the first application, we compare computed solutions for flow over a hypersonic cylindrical leading edge with available experimental data. In the second application, we look at solutions for flow over an aerodynamically heated panel. [ABSTRACT FROM AUTHOR]

Abstract Cryogenic wind tunnel is a sophisticated aerodynamics ground test facility, which operates in cryogenic temperature with injection of liquid nitrogen. The multi-variable, nonlinear and coupled dynamics existing between the temperature, pressure and Mach number in the tunnel, poses great challenges for the effective control of the tunnel. L 1 adaptive control is a new control methodology developed in recent years with good robustness properties, which has good potentials to address these challenges. But this control method does not provide full adaptive feedforward control in its generic structure. In the paper, adaptive feedforward control action is introduced into the standard L 1 adaptive control architecture for nonlinear systems in the presence of matched un-modeled dynamics. This new control structure is applied to the stagnation pressure control in a cryogenic wind tunnel, which could also be used for the control of temperature and Mach number in the tunnel. This new method could effectively compensate known disturbances with linear gain uncertainty, which occur in the nonlinear systems, while retaining the closed-loop control performance of L 1 adaptive control. After the proof and discussions on the stability of this method, simulations of the stagnation pressure control in the wind tunnel are presented. The results and analysis demonstrate the effectiveness of the proposed control architecture.

We consider a three-dimensional unsteady flow with one, two, or four rotating detonation waves arising in an annular gap of an axially symmetric device between two parallel planes perpendicular to its symmetry axis. The corresponding problem is formulated and studied. It is assumed that there is a reservoir with quiescent homogeneous propane–air combustible mixture with given stagnation parameters; the mixture flows from the reservoir into the annular gap through its external cylindrical surface toward the symmetry axis, and the parameters of the mixture are determined by the pressure in the reservoir and the static pressure in the gap. The detonation products flow out from the gap into a space bounded on one side by an impermeable wall that is an extension of a side of the gap. Through a hole on the other side of the gap and through a conical output section with a half-opening angle of 45 ∘ , the gas flows out from the engine into the external space. We formulate a model of detonation initiation by energy supply in which the direction of rotation of the detonation wave is defined by the position of the energy-release zone of the initiator with respect to the solid wall situated in a plane passing through the symmetry axis. After a while, this solid wall disappears (burns out). We obtain and analyze unsteady shock-wave structures that arise during the formation of a steady rotating detonation. We measure and compare thrust characteristics for different numbers of detonation waves. It was shown that the thrust weakly depends on the number of waves while the specific impulse increases with increasing number of waves. The study of rotating detonation at various values of the stagnation pressure was conducted. The calculation results show that at a stagnation pressure less than the critical value, the realization of rotating detonation is impossible. It is established that, depending on the stagnation pressure, qualitatively different shock-wave structures can be observed. The analysis is carried out within single-stage combustion kinetics by the numerical method based on the Godunov scheme with the use of an original software system developed for multi-parameter calculations and visualization of flows. The calculations were carried out on the Lomonosov supercomputer at Moscow State University. [ABSTRACT FROM AUTHOR]

Copyright of Nuclear Safety is the property of Nuclear & Radiation Safety Center and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The mechanical characteristics and stress state caused by water jet loading are influenced by many factors that have restricted studies on the jet mechanism. Using the basic theory of elasticity and fluid dynamics, the mechanical effects of water jet loading are analyzed. Based on the simplified jet distribution pressure, the elastic analytical solution of the stress distribution in a semi-infinite plane under the jet distribution pressure is derived, and the stress distribution characteristics are discussed. In addition, the Mohr–Coulomb yield criterion served as a fracture criterion, enabling establishment of the relationship between jet pressure and rock strength. The results indicate that the compressive stress is symmetrically distributed around the jet axis with the maximum at the center. Conversely, the shear stress is Anti-symmetrically distributed around the jet axis with the maximum at the point (0.5r, ± 0.65r). The initial fracture of rock under the impact of water jet is mainly shear compression failure. The Mohr–Coulomb yield criterion is useful for estimating the relationships between the rock failure zone diameter with the water jet impact pressure. [ABSTRACT FROM AUTHOR]

The present study focuses on the impact of the underlying RANS turbulence model in the Zonal Detached Eddy Simulation (ZDES) method when used for secondary flow prediction. This is carried out in light of three issues commonly investigated for hybrid RANS/LES methods (detection and protection of attached boundary layer, emergence, and growth of resolved turbulent fluctuations and accurate prediction of separation front due to progressive adverse pressure gradient). The studied configuration is the first rotor of a high pressure compressor. Three different turbulence modelings (Spalart and Allmaras model (SA), Menter model with (SST) and without (BSL) shear stress correction) are assessed as ZDES underlying turbulence model and also as turbulence model of unsteady RANS simulations. Whatever the underlying turbulence model, the ZDES behaves well with respect to the first two issues as the boundary layers appear effectively shielded and the RANS-to-LES switch is close downstream of trailing edges and separation fronts leading to a quick LES treatment of wakes and shear layers. Both tip leakage and corner flows are strongly influenced by the Navier-Stokes resolution approach (unsteady RANS vs. ZDES) but the underlying turbulence modelling (SA vs. SST vs. BSL) impacts mainly the junction flow near the hub for both approaches. ZDES underlying turbulence model choice appear essential since it leads to quite different corner flow separation topologies and so to inversion of the downstream stagnation pressure radial gradient. [ABSTRACT FROM AUTHOR]

This study explores the effect of differing inlet and outlet boundary conditions on the operation and performance of a rotating detonation combustor (RDC) over an annulus mass flux range of 50 to 210 kg s − 1 m − 2 and equivalence ratios of 0.7, 1.0, and 1.3. The RDC is equipped with either a uniform outlet restriction or with a set of nozzle guide vanes to simulate turbine integration. Stagnation pressure data from Kiel probes placed in the high-enthalpy exhaust flow are presented for the operational envelope. The RDC's operation is categorized into different modes distinguished by the number of co- and counter-rotating combustion waves in the annulus. With increasing mass flux, a typical progression proceeding from a pair of counter-rotating waves, to a single detonation wave, and then further to multiple co-rotating waves is observed with wave speeds reaching up to 84% of the CJ velocity. It is shown that a choking condition at the outlet throat correlates with the transition from two counter-rotating waves to a single wave detonation regime. The channel Mach number is then calculated from measured pressure ratios and is shown to agree with area ratio-based estimates. The pressure gain of the RDC is expressed as the stagnation pressure change from the air plenum to the outlet throat, and it is shown that the specific operating mode of the device – in conjunction with the chosen injector and outlet area ratios – can significantly decrease the pressure gain performance in some cases, while not significantly affecting it in others. While no positive pressure gain was achieved in the experiments, the presented experimental data compare well with numerical results of similar boundary conditions and underline the importance of minimizing injector pressure loss while applying outlet restrictions to the combustor. The data also suggest that specific geometric combinations may lead to adverse modes such as longitudinally pulsing combustion, resulting in a reduction in the measured pressure gain relative to numerical results. This observation occurs more often for geometric combinations which are the most promising for exhibiting positive pressure gain, and suppressing these modes will be an important topic to achieving this goal. It is further shown that transition regions exist between modes of one and multiple co-rotating waves, and that wave multiplication may be necessary to unlock further increases in the pressure gain. [ABSTRACT FROM AUTHOR]

"Water cold resulting in inhibition of the wood" refers to that kidney yang deficiency and cold coagulation in the kidney may lead to failune of the kidney to warm the liver and liver qi stagnation. This pathogenesis originated from the Huangdi Neijing (HuangdV s Internal Classic), and has been developed and applied to diseases of various systems by later physicians. Based on literature research, it is observed that this pathogenesis could possibly be applied in interpreting the mechanism of Parkinson' s disease with depression (PDD) from TCM perspective. For PDD, yang deficiency and cold coagulation of the kidney is the root of the attack, and liver qi stagnation appears in the initial stage. According to various clinical studies, the therapeutic method of warming the kidney yang to relieve liver qi stagnation is effective in treating PDD. Based on such findings, we have developed a formula (composed of Zhifuzi (prepared aconite root, Radix Aconiti Lateralis Praeparata), Bajitian (morinda root,Radix Morindae Officinalis), Chaihu (bupleurum, Radix Bupleuri)) with corresponding effects, which proves to be 70% effective. Pharmacological studies also show that certain traditional Chinese medicinals with the effect of warming the kidney or relieving the liver qi stagnation can show some effect in the treatment of PDD. These research results support the exploration of the pathogenesis of PDD from the perspective of "water cold resulting in inhibition of the wood". This article has explored such a pathogenesis in PDD based on literature reviews of classical TCM literature, relevant theories and modern studies, in order to provide new ideas and references for the pathogenesis research and clinical treatment of PDD. [ABSTRACT FROM AUTHOR]

Cryogenic wind tunnel is a sophisticated aerodynamics ground test facility, which operates in cryogenic temperature with injection of liquid nitrogen. The multi-variable, nonlinear and coupled dynamics existing between the temperature, pressure and Mach number in the tunnel, poses great challenges for the effective control of the tunnel. L1 adaptive control is a new control methodology developed in recent years with good robustness properties, which has good potentials to address these challenges. But this control method does not provide full adaptive feedforward control in its generic structure. In the paper, adaptive feedforward control action is introduced into the standard L1 adaptive control architecture for nonlinear systems in the presence of matched un-modeled dynamics. This new control structure is applied to the stagnation pressure control in a cryogenic wind tunnel, which could also be used for the control of temperature and Mach number in the tunnel. This new method could effectively compensate known disturbances with linear gain uncertainty, which occur in the nonlinear systems, while retaining the closed-loop control performance of L1 adaptive control. After the proof and discussions on the stability of this method, simulations of the stagnation pressure control in the wind tunnel are presented. The results and analysis demonstrate the effectiveness of the proposed control architecture. [ABSTRACT FROM AUTHOR]

The aim of this work is to develop a calculation model based on the method of characteristics making it possible to study the effect of the stagnation pressure of the combustion chamber on the 2D and axisymmetric minimum length nozzle design giving a uniform and parallel flow at the exit section. The model is based on the use of the real gas approach. The co-volume and the intermolecular interaction effect are taken into account by the use of the Berthelot state equation. The effect of molecular vibration is considered in our model to evaluate the behaviour of gas at a high temperature. In this case, the stagnation pressure and the stagnation temperature are important parameters in our model. The resolution of the algebraic equations is done by the finite difference corrector predictor algorithm. The validation of the results is controlled by the convergence of the critical section ratios calculated numerically as obtained by the theory. The mass and the thrust are evaluated to improve the efficiency of the nozzle. The comparison is made with the high temperature and perfect gas models. The application is made for air. [ABSTRACT FROM AUTHOR]

Submarine debris flows have a significant impact on offshore and coastal facilities. The unique characteristics of submarine debris flows involve large mass movements and long travel distances over very gentle slopes. To improve our insight and knowledge of the basic mechanism behind submarine debris flows, an analytical model was derived for the mobility of submarine debris flows. This model takes into account the mass change of debris flows induced by deposition, stagnation pressure, and the topography of the depositional area. One case study on the Palos Verdes debris flow proves its ability to predict the run-out distance of a submarine debris flow to a reasonable level of accuracy. On the gentle slopes, the submarine debris flow progressively loses mass due to deposition, which in turn influences the flow velocity. In addition, the results show that the slope angle and spreading angle of the debris depositional zone play important roles in the sliding process. [ABSTRACT FROM AUTHOR]

Highlights • Mixing augmentation mechanisms of three devices were analyzed and compared. • Streamwise vorticity induced by additional vorticity is the main reason for mixing enhancement. • Stagnation pressure loss induced by the pulsed jet is small. • Air jet enhances mixing and reduces the hydrogen distribution on the bottom. • Ramp has a highly remarkable improvement on mixing efficiency and penetration depth. Abstract Numerical investigation of some mixing enhancement strategies based on the traditional transverse injection technique proposed in recent years was carried out by means of the three-dimensional Reynolds-average Navier–Stokes (RANS) equations coupled with the two equation k-ω shear stress transport (SST) turbulence model. The numerical approaches employed in the current study were validated against the available two- and three-dimensional data in the open literature, and they can be used with confidence to achieve a better understanding of mixing augmentation mechanisms in transverse injection flow fields with various mixing enhancement strategies, namely the pulsed jet, the air jet and the ramp. Results obtained in this study provide important insight into complex flow phenomena. Various fundamental mechanisms dictating the intricate flow characteristics for the transverse injection flow field with various mixing enhancement strategies, including the circulation, vertical structures, velocity vectors and shock wave systems, have been analyzed systematically. The performance parameters of the transverse injection flow fields, such as the mixing length, the fuel penetration depth and the stagnation pressure loss have been compared. Different mixing enhancement strategies have their advantages and disadvantages, and the combination of various mixing enhancement strategies may be a promising injection strategy for better mixing performance of the transverse injection flow field. A stronger streamwise vorticity is the main reason for the mixing enhancement. However, the mixing length and the stagnation pressure loss of the transverse injection flow field show opposite trends from each other with a variance in the intensity of streamwise vorticity. [ABSTRACT FROM AUTHOR]

Abstract In this paper we present the first exploration of detonation wave propagation dynamics in premixed supersonic flows using a novel rotating detonation engine (RDE) configuration. An RDE with a coupled linear extension, referred to as ρ DE, is used to divide detonations traveling radially in the RDE into linearly propagating waves. A tangential propagating wave is directed down a modular tangential linearized extension to the engine for ease of optical diagnostics and hardware configuration investigations. A premixed Mach 2 supersonic linear extension is coupled to the ρ DE to investigate the effects of varying crossflow configurations for detonation propagation, particularly the interaction between detonations and supersonic reactive mixtures. Detonation waves are generated at the steady operating frequency of the RDE and visualized using high speed schlieren and broadband OH* chemiluminescence imaging. The stagnation pressure was varied from over- to ideally-expanded supersonic regimes. Experimental analysis of detonation interaction with the supersonic regimes show that the detonation propagates freely in the ideally-expanded regime. Deflagration-to-detonation transition (DDT) occurs in the over-expanded regime. Based on the data collected, the DDT process favors supersonic flow with higher source pressures. Highlights • First exploration of detonation propagation in a novel H 2 -air premixed supersonic rotating detonation engine (RDE). • The stagnation pressure was varied from over- to ideally-expanded supersonic regimes. • The detonation propagates freely in the ideally-expanded supersonic regime. • Deflagration-to-detonation transition (DDT) occurs in the over-expanded regime. [ABSTRACT FROM AUTHOR]

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. Motivated by a scenario of incomplete chemical decomposition within a miniaturized, microfabricated monopropellant micropropulsion system, the multiphase flow is modeled over a range of throat Reynolds numbers (160=Ret=780) to consist of liquid droplets ranging in size from 0.1 to 3.0 µm in diameter (Stokes numbers 0.01-10.0) and with mass loadings up to 100% relative to the gas phase. The results indicate that the presence of liquid droplets within the supersonic gas flow can substantially degrade micronozzle performance with thrust reductions approaching 19% and specific impulse reductions of up to 35% possible for sub-micrometer-scale droplets at Ret=780 and a mass loading of 100%. [ABSTRACT FROM AUTHOR]

The flow parameters control in wind tunnels is an area of intense research in recent years, with the aim of improving quality and efficiency of the wind tunnel operation. In this paper, an attempt is made to contribute to a better understanding of the stagnation pressure control in supersonic blowdown-type facilities. The stagnation pressure control strategy in the VTI Belgrade T-38 wind tunnel is discussed. An improved mathematical model for a supersonic wind tunnel is suggested and applied to the T-38 facility. Comparisons of simulation and experimental data are made to demonstrate accurate prediction of the facility response in supersonic flow conditions by the mathematical model. The model is used to incorporate a modified feedforward control in the original T-38 wind tunnel control system. The actual wind tunnel tests confirm model-predicted decrease of flow stabilization time and increase of available measurement time, bringing significant improvement in the wind tunnel operation efficiency.