Direct numerical simulation of shock/turbulent boundary layer interaction in a supersonic compression ramp

A direct numerical simulation of the shock/turbulent boundary layer interaction flow in a supersonic 24-degree compression ramp is conducted with the free stream Mach number 2.9.The blow-and-suction disturbance in the upstream wall boundary is used to trigger the transition.Both the mean wall pressure and the velocity profiles agree with those of the experimental data,which validates the simulation.The turbulent kinetic energy budget in the separation region is analyzed.Results show that the turbulent production term increases fast in the separation region,while the turbulent dissipation term reaches its peak in the near-wall region.The turbulent transport term contributes to the balance of the turbulent conduction and turbulent dissipation.Based on the analysis of instantaneous pressure in the downstream region of the mean shock and that in the separation bubble,the authors suggest that the low frequency oscillation of the shock is not caused by the upstream turbulent disturbance,but rather the instability of separation bubble.

Reflected shock/turbulent boundary layer interaction structure analysis based on large eddy simulation

In order to understand the physical phenomenon of the reflected shock/turbulent boundary layer interaction,the Large Eddy Simulation(LES)is conducted to investigate shock wave and turbulent boundary layer interaction in a 12°compression ramp with inlet high Mach number of 2.9.Rescaling/recycling method is used as inflow turbulence generation technique and validated on a supersonic flat plate turbulent boundary layer.The flow field of recycling plane in the plate computation domain is obtained to give the inlet boundary condition for the LES computation.This paper focuses on the reflected shock/turbulent boundary layer interaction region,where the fine flow structure and instantaneous flow field are analyzed in detail.It is found that the unsteady motion of the shock wave leads to the increase of wall pressure fluctuation.

Turbulent Image Restoration in Atmosphere with Cyclopean Processing via Binocular Fusion

The outstanding issue to overcoming atmospheric turbulence on distant imaging is a fundamental interest and technological challenge.We propose a novel scenario and technique to restore the optical image in turbulent environmental by referring to Cyclopean image with binocular vision.With human visual intelligence,image distortion resulting from the turbulence is shown to be substantially suppressed.Numerical simulation results taking into account of the atmospheric turbulence,optical image system,image sensors,display and binocular vision perception are presented to demonstrate the robustness of the image restoration,which is compared with a single channel planar optical imaging and sensing.Experiment involving binocular telescope,image recording and the stereo-image display is conducted and good agreement is obtained between the simulation with perceptive experience.A natural extension of the scenario is to enhance the capability of anti-vibration or anti-shaking for general optical imaging with Cyclopean image.

AERODYNAMIC HEATING IN THE REGION OF SHOCK AND TURBULENT BOUNDARY LAYER INTERACTION INDUCED BY A CYLINDER

Detailed distributions of heat flux in the region of shock wave and turbulent boundary layer interaction induced by a cylinder were measured in the shock tunnel Oil flow patterns and Schlieren photo- graphs were taken.Empirical relations were given for determining separation shock angle,peaks of heat flux and their locations on both cylinder leading edge and flat plate surface,and other characteristic parameters of the interaction region.

Numerical study on the turbulent mixing of planar shock-accelerated triangular heavy gases interface

The interaction of a planar shock wave with a triangle-shaped sulfur hexafluoride (SF6) cylinder surrounded by air is numerically studied using a high resolution finite volume method with minimum dispersion and controllable dissipation reconstruction.The vortex dynamics of the Richtmyer-Meshkov instability and the turbulent mixing induced by the KelvinHelmholtz instability are discussed.A modified reconstruction model is proposed to predict the circulation for the shock triangular gas-cylinder interaction flow.Several typical stages leading the shock-driven inhomogeneity flow to turbulent mixing transition are demonstrated.Both the decoupled length scales and the broadened inertial range of the turbulent kinetic energy spectrum in late time manifest the turbulent mixing transition for the present case.The analysis of variable-density energy transfer indicates that the flow structures with high wavenumbers inside the Kelvin-Helmholtz vortices can gain energy from the mean flow in total.Consequently,small scale flow structures are generated therein by means of nonlinear interactions.Furthermore,the occasional 'pairing' between a vortex and its neighboring vortex will trigger the merging process of vortices and,finally,create a large turbulent mixing zone.

Comparison of ERA5 turbulent fluxes at the air-sea interface with measurements from a wave-following platform

Turbulent fluxes at the air-sea interface were estimated with data collected in 2011-2020 with a low-profile platform named OCARINA during eight experiments in five regions:2011,2015,and 2016 in the Iroise Sea;2012 in the tropical Atlantic;2014 in the Chilie-Peru upwelling;2017 and 2018 in the Mediterranean Sea,and 2018 and 2020 in Barbados.The observations were carried out with moderate winds(2-10 m s^(-1))and average wave heights of 1.5 m.In this study,the authors used the fluxes calculated by the bulk method using OCARINA-sampled data as the input.These data can validate the fluxes estimated from ERAS reanalysis data.The OCARINA and ERA5 data were taken concomitantly.To do this,the authors established an algorithm to extract the OCARINA data as closely as possible to the reanalysis data in time and position.The measurements of the OCARINA platform can conclude on the relevance of the widely used reanalysis data.

Numerical Simulation of Turbulent Diffusion Flames of a Biogas Enriched with Hydrogen

Any biogas produced by the anaerobic fermentation of organic materials has the advantage of being an environmentally friendly biofuel.Nevertheless,the relatively low calorific value of such gases makes their effective utilization in practical applications relatively difficult.The present study considers the addition of hydrogen as a potential solution to mitigate this issue.In particular,the properties of turbulent diffusion jet flames and the related pollutant emissions are investigated numerically for different operating pressures.The related numerical simulations are conducted by solving the RANS equations in the frame of the Reynolds Stress Model in combination with the flamelet approach.Radiation effects are also taken into account and the combustion kinetics are described via the GRI-Mech 3.0 reaction model.The considered hydrogen fuel enrichment spans the range from 0%to 50%in terms of volume.Pressure varies between 1 and 10 atm.The results show that both hydrogen addition and pressure increase lead to an improvement in terms of mixing quality and have a significant effect on flame temperature and height.They also reduce CO_(2) emissions but increase NOx production.Prompt NO is shown to be the predominant NO formation mechanism.

The Turbulent Schmidt Number for Transient Contaminant Dispersion in a Large Ventilated Room Using a Realizable k-εModel

Buildings with large open spaces in which chemicals are handled are often exposed to the risk of explosions.Computational fluid dynamics is a useful and convenient way to investigate contaminant dispersion in such large spaces.The turbulent Schmidt number(Sc_(t))concept has typically been used in this regard,and most studies have adopted a default value.We studied the concentration distribution for sulfur hexafluoride(SF_(6))assuming different emission rates and considering the effect of Sc_(t).Then we examined the same problem for a light gas by assuming hydrogen gas(H_(2))as the contaminant.When SF_(6) was considered as the contaminant gas,a variation in the emission rate completely changed the concentration distribution.When the emission rate was low,the gravitational effect did not take place.For both low and high emission rates,an increase in S_(ct) accelerated the transport rate of SF_(6).In contrast,for H_(2) as the contaminant gas,a larger S_(ct) could induce a decrease in the H_(2) transport rate.

Analytical solutions of turbulent boundary layer beneath forward-leaning waves

As a typical nonlinear wave,forward-leaning waves can be frequently encountered in the near-shore areas,which can impact coastal sediment transport significantly.Hence,it is of significance to describe the characteristics of the boundary layer beneath forward-leaning waves accurately,especially for the turbulent boundary layer.In this work,the linearized turbulent boundary layer model with a linear turbulent viscosity coefficient is applied,and the novel expression of the near-bed orbital velocity that has been worked out by the authors for forward-leaning waves of arbitrary forward-leaning degrees is further used to specify the free stream boundary condition of the bottom boundary layer.Then,a variable transformation is found so as to make the equation of the turbulent boundary layer model be solved analytically through a modified Bessel function.Consequently,an explicit analytical solution of the turbulent boundary layer beneath forward-leaning waves is derived by means of variable separation and variable transformation.The analytical solutions of the velocity profile and bottom shear stress of the turbulent boundary layer beneath forward-leaning waves are verified by comparing the present analytical results with typical experimental data available in the previous literature.

Stochastic Analysis and Modeling of Velocity Observations in Turbulent Flows

Highly turbulent water flows,often encountered near human constructions like bridge piers,spillways,and weirs,display intricate dynamics characterized by the formation of eddies and vortices.These formations,varying in sizes and lifespans,significantly influence the distribution of fluid velocities within the flow.Subsequently,the rapid velocity fluctuations in highly turbulent flows lead to elevated shear and normal stress levels.For this reason,to meticulously study these dynamics,more often than not,physical modeling is employed for studying the impact of turbulent flows on the stability and longevity of nearby structures.Despite the effectiveness of physical modeling,various monitoring challenges arise,including flow disruption,the necessity for concurrent gauging at multiple locations,and the duration of measurements.Addressing these challenges,image velocimetry emerges as an ideal method in fluid mechanics,particularly for studying turbulent flows.To account for measurement duration,a probabilistic approach utilizing a probability density function(PDF)is suggested to mitigate uncertainty in estimated average and maximum values.However,it becomes evident that deriving the PDF is not straightforward for all turbulence-induced stresses.In response,this study proposes a novel approach by combining image velocimetry with a stochastic model to provide a generic yet accurate description of flow dynamics in such applications.This integration enables an approach based on the probability of failure,facilitating a more comprehensive analysis of turbulent flows.Such an approach is essential for estimating both short-and long-term stresses on hydraulic constructions under assessment.

A turbulent mass diffusivity model for analyzing the mixing characteristics in an impinging stream-rotating packed bed

In this study,the fluid flow and mixing process in an impinging stream-rotating packed bed(IS-RPB)is simulated by using a new three-dimensional computational fluid dynamics model.Specifically,the gaseliquid flow is simulated by the Euler-Euler model,the hydrodynamics of the reactor is predicted by the RNG k-εmethod,and the high-gravity environment is simulated by the sliding mesh model.The turbulent mass transfer process is characterized by the concentration variance c^(2) and its dissipation rateεc formulations,and therefore the turbulent mass diffusivity can be directly obtained.The simulated segregation index Xs is in agreement with our previous experimental results.The simulated results reveal that the fringe effect of IS can be offset by the end effect at the inner radius of RPB,so the investigation of the coupling mechanism between IS and RPB is critical to intensify the mixing process in IS-RPB.

Study on Compressible Turbulent Boundary Layer Multiple Shock Wave Interaction in the Duct

The structure and trubulence phenomena of multiple shock wave /turbulent boundary layer interaction (MSW-TBLI) in a square duct were investigated using flow visualization methods and a two-component Laser Doppler Velocimeter (LDV ). First - the MSW-TBLI was visualized by schlieren photography and laser holographic interferography. Second, the time-mean and fluctuating velocities in the MSW-TBLI were explored in detail using LDV Spatial distributions of turbulence intensity,Reynolds shear stress and turbulence kinetic energy are presented.

A CALCULATING METHOD OF SHOCK WAVE OSCILLATING FREQUENCY DUE TO TURBULENT SHEAR LAYER FLUCTUATIONS IN SUPERSONIC FLOW

One of the more severe fluctuating pressure environments encountered in supersonic or hypersonic flows is the shock wave oscillation driven by interaction of a shock wave with boundary layer. The high intensity oscillating shock wave may induce structure resonance of a high speed vehicle. The research for the shock oscillation used to adopt empirical or semiempirical methods because the phenomenon is very complex. In this paper a theoretical solution on shock oscillating frequency due to turbulent shear layer fluctuations has been obtained from basic conservation equations. Moreover, we have attained the regularity of the frequency of oscillating shock varying with incoming flow Much numbers M and turning angle . The calculating results indicate excellent agreement with measurements. This paper has supplied a valuable analytical method to study aeroelastic problems produced by shock wave oscillation.

Observing the air-sea turbulent heat flux on the trajectory of tropical storm Danas

Tropical cyclones constitute a major risk for coastal communities.To assess their damage potential,accurate predictions of their intensification are needed,which requires a detailed understanding of the evolution of turbulent heat flux(THF).By combining multiple buoy observations along the south north storm track,we investigated the THF anomalies associated with tropical storm Danas(2019)in the East China Sea(ECS)during its complete life cycle from the intensification stage to the mature stage and finally to its dissipation on land.The storm passage is characterized by strong winds of 10-20 m/s and a sea level pressure below 1000 hPa,resulting in a substantial enhancement of THF.Latent heat(LH)fluxes are most strongly affected by wind speed,with a gradually increasing contribution of humidity along the trajectory.The relative contributions of wind speed and temperature anomalies to sensible heat(SH)depend on the stability of the boundary layer.Under stable conditions,SH variations are driven by wind speed,while under near-neutral conditions,SH variations are driven by temperature.A comparison of the observed THF and associated variables with outputs from the ERA 5 and MERRA 2 reanalysis products reveals that the reanalysis products can reproduce the basic evolution and composition of the observed THF.However,under extreme weather conditions,temperature and humidity variations are poorly captured by ERA 5 and MERRA 2,leading to large LH and SH errors.The differences in the observed and reproduced LH and SH during the passage of Danas amount to 26.1 and 6.6 W/m^(2) for ERA 5,respectively,and to 39.4 and 12.5 W/m^(2) for MERRA 2,respectively.These results demonstrate the need to improve the representation of tropical cyclones in reanalysis products to better predict their intensification process and reduce their damage.

Near-wall behaviors of oblique-shock-wave/turbulent-boundary-layer interactions

A direct numerical simulation （DNS） on an oblique shock wave with an incident angle of 33.2° impinging on a Mach 2.25 supersonic turbulent boundary layer is performed. The numerical results are confirmed to be of high accuracy by comparison with the reference data. Particular efforts have been made on the investigation of the near-wall behaviors in the interaction region, where the pressure gradient is so significant that a certain separation zone emerges. It is found that, the traditional linear and loga- rithmic laws, which describe the mean-velocity profiles in the viscous and meso sublayers, respectively, cease to be valid in the neighborhood of the interaction region, and two new laws of the wall are proposed by elevating the pressure gradient to the leading order. The new laws are inspired by the analysis on the incompressible separation flows, while the compressibility is additionally taken into account. It is verified by the DNS results that the new laws are adequate to reproduce the mean-velocity profiles both inside and outside the interaction region. Moreover, the normalization adopted in the new laws is able to regularize the Reynolds stress into an almost universal distribution even with a salient adverse pressure gradient （APG）.

HEATING CHARACTERISTICS OF BLUNT SWEPT FIN-INDUCED SHOCK WAVE TURBULENT BOUNDARY LAYER INTERACTION

An experimental study was conducted on shock wave turbulent boundary layer interactions caused by a blunt swept fin-plate configuration at Mach numbers of 5.0, 7.8, 9.9 for a Reynolds number range of (1.0.similar to 4.7) x 10(7)/m. Detailed heat transfer and pressure distributions were measured at fin deflection angles of up to 30 degrees for a sweepback angle of 67.6 degrees. Surface oil flow patterns and liquid crystal thermograms as well as schlieren pictures of fin shock shape were taken. The study shows that the flow was separated at deflection of 10 degrees and secondary separation were detected at deflection of theta greater than or equal to 20 degrees. The heat transfer and pressure distributions on flat plate showed an extensive plateau region followed by a distinct dip and local peak close to the fin foot. Measurements of the plateau pressure and heat transfer were in good agreement with existing prediction methods, but pressure and heating peak measurements at M greater than or equal to 6 were significantly lower than predicted by the simple prediction techniques at lower Mach numbers.

Septic shock due to cytomegalovirus colitis associated with rituximab use:A case report

BACKGROUND Cytomegalovirus(CMV)infections can cause significant morbidity and mortality in immunocompromised individuals.CMV targets dysfunctional lymphocytes.Chronic rituximab(RTX)therapy can cause B-lymphocyte dysfunction,increasing CMV risk.Rarely,CMV infections present with critical illness such as septic shock.CASE SUMMARY A 64-year-old African American woman presented with generalized weakness and non-bloody watery diarrhea of 4-6 weeks duration.She did not have nausea,vomiting or,abdominal pain.She had been on monthly RTX infusions for neuromyelitis optica.She was admitted for septic shock due to pancolitis.Blood investigations suggested pancytopenia and serology detected significantly elevated CMV DNA.Valganciclovir treatment led to disease resolution.CONCLUSION This case illustrates an extremely rare case of CMV colitis associated with RTX use presenting with septic shock.High suspicion for rare opportunistic infections is imperative in individuals with long-term RTX use.

Prognostic impact of hypernatremia for septic shock patients in the intensive care unit

BACKGROUND Hypernatremia represents a significant electrolyte imbalance associated with numerous adverse outcomes,particularly in cases of intensive care unit(ICU)-acquired hypernatremia(IAH).Nevertheless,its relevance in patients with septic shock remains uncertain.AIM To identify independent risk factors and their predictive efficacy for IAH to improve outcomes in patients with septic shock.METHODS In the present retrospective single-center study,a cohort of 157 septic shock patients with concurrent hypernatremia in the ICU at The First Affiliated Hospital of Soochow University,between August 1,2018,and May 31,2023,were analyzed.Patients were categorized based on the timing of hypernatremia occurrence into the IAH group(n=62),the non-IAH group(n=41),and the normonatremia group(n=54).RESULTS In the present study,there was a significant association between the high serum sodium concentrations,excessive persistent inflammation,immunosuppression and catabolism syndrome and chronic critical illness,while rapid recovery had an apparent association with normonatremia.Moreover,multivariable analyses revealed the following independent risk factors for IAH:Total urinary output over the preceding three days[odds ratio(OR)=1.09;95%CI:1.02–1.17;P=0.014],enteral nutrition(EN)sodium content of 500 mg(OR=2.93;95%CI:1.13–7.60;P=0.027),and EN sodium content of 670 mg(OR=6.19;95%CI:1.75–21.98;P=0.005)were positively correlated with the development of IAH.Notably,the area under the curve for total urinary output over the preceding three days was 0.800(95%CI:0.678–0.922,P=0.001).Furthermore,maximum serum sodium levels,the duration of hypernatremia,and varying sodium correction rates were significantly associated with 28-day in-hospital mortality in septic shock patients(P<0.05).CONCLUSION The present findings illustrate that elevated serum sodium level was significantly associated with a poor prognosis in septic shock patients in the ICU.It is highly recommended that hypernatremia be considered a potentially important prognostic indicator for the outcome of septic shock.

NUMERICAL SIMULATION AND ANALYSIS OF HORSESHOE-SHAPED VORTEX IN NEAR-WALL REGION OF TURBULENT BOUNDARY LAYER

The low-Reynolds-number full developed turbulent flow in channels is simulated using large eddy simulation（LES）method with the preconditioned algorithm and the dynamic subgrid-scale model,with a given disturbance in inlet boundary,after a short development section.The inlet Reynolds number based on momentum thickness is 670.The computed results show good agreement with direct numerical simulation（DNS）,which include root mean square fluctuated velocity distribution and average velocity distribution.It is also found that the staggered phenomenon of the coherent structures is caused by sub-harmonic.The results clearly show the formation and evolution of horseshoe vortex in the turbulent boundary layer,including horseshoe vortex structure with a pair of streamwise vortexes and one-side leg of horseshoe vortex.Based on the results,the development of the horseshoe-shaped coherent structures is analyzed in turbulent boundary layer.

HYBRID SCHEME FOR COMPRESSIBLE TURBULENT FLOW AROUND CURVED SURFACE BODY

A hybrid central-upwind scheme is proposed. Two sub-schemes, the central difference scheme and the Roets flux difference splitting scheme, are hybridized by means of a binary sensor function. In order to examine the capability of the proposed hybrid scheme in computing compressible turbulent flow around a curved surface body, especially the flow involving shock wave, three typical eases are investigated by using detached-eddy simulation technique. Numerical results show good agreements with the experimental measurements. The present hybrid scheme can be applied to simulating the compressible flow around a curved surface body involving shock wave and turbulence.