In hypersonic boundary layers,the optimal disturbance is notably caused by normalmode instabilities,such as Mack second mode.However,recent experimental and numerical efforts have demonstrated the dominance of nonmoda...In hypersonic boundary layers,the optimal disturbance is notably caused by normalmode instabilities,such as Mack second mode.However,recent experimental and numerical efforts have demonstrated the dominance of nonmodal growth in hypersonic flows with the presence of moderate nose bluntness.In this study,resolvent analysis and parabolized stability equation analysis are performed to investigate the instabilities over a blunt-tip wedge.Main parameters include Mach number 5.9,unit Reynolds number 91.5×10~6/m,half wedge angle 5°,and nose radii ranging from 2.54 mm to 15.24 mm.Two novel growth patterns of travelling waves are identified to compete,whose nature is the intersection of the energy gain of optimal and sub-optimal disturbances.Pattern A with large spanwise wavelengths has the signature of slow energy amplification over a long distance which concentrates in the entropy layer.By contrast,pattern B with relatively small spanwise wavelengths presents rapid transient growth inside the boundary layer.A systematic study is performed on the growth/attenuation mechanism of disturbance patterns and the effects of wall temperature and nose radius.Wall cooling is found to be an alternative control strategy aimed at nonmodal instabilities.The receptivity to slow acoustic waves is considered when the effect of bluntness is studied.An estimated amplitude response favorably reproduces the reversal-like phenomenon.The lift-up/Orr mechanism analysis provides an explanation of energy growth for nonmodal responses.展开更多
The primary Mach Reflection(MR)and pressure/heating loads on V-shaped Blunt Leading Edges(VBLEs)with variable elliptic cross-sections and conic crotches are theoretically investigated in this study.The simplified cont...The primary Mach Reflection(MR)and pressure/heating loads on V-shaped Blunt Leading Edges(VBLEs)with variable elliptic cross-sections and conic crotches are theoretically investigated in this study.The simplified continuity method is used to forecast the shock configurations.The theoretical predictions and the numerical simulations for the Mach stem and the triple point as well as the curved shock accord well.Based on the theoretical model,an analysis of the impact of the axial ratio a/b of the cross-sectional shape and the eccentricity e of the crotch sweep path on shock structures is carried out.The shock configurations obtained from the theoretical model enable the derivation of the transition boundaries between the primary MR and the same family Regular Reflection(sRR).It is found that the increase of a/b and e can both facilitate the primary MR to sRR transition.The resulting transition and the corresponding generation of the wall pressure and heat flux are then investigated.The results indicate that higher values of the ratio a/b can significantly reduce the wall pressure and heating loads by inducing the primary MR to sRR transition.Conversely,the increase in the eccentricity e results in increased loads,despite causing the same transition.展开更多
Vortex-induced vibration of hydrofoils is concerned with structural safety and noise level in hydraulic machinery and marine engineering.The research on vibration characteristics under different operating conditions i...Vortex-induced vibration of hydrofoils is concerned with structural safety and noise level in hydraulic machinery and marine engineering.The research on vibration characteristics under different operating conditions is significant.In this study,numerical simulations are conducted to investigate the vortex-induced vibration responses of an elastically suspended hydrofoil with blunt trailing edge in pitch direction.The work studies the effects of four parameters,namely the structural natural frequency,mass ratio,initial attack angle,and Reynolds number on vibration characteristics,with special emphasis on frequency lock-in.Results indicate that as the structural natural frequency changes,the vibration amplitude may increase substantially within a certain frequency range,in which the vortex shedding frequency locks into the structural natural frequency,and frequency lock-in occurs.In addition,with increasing the mass ratio,the frequency range of lock-in becomes narrower,and both the upper and lower thresholds decrease.As the initial attack angle increases from 0◦to 6◦,the lock-in range gets reduced.Over the three Reynolds numbers(6×10^(5),9×10^(5),and 12×10^(5)),the lock-in range remains virtually unchanged.Moreover,for a certain structural natural frequency,modifying the mass ratio,initial attack angle,and Reynolds number could effectively suppress the vibration amplitude.展开更多
BACKGROUND The spleen is the most commonly injured solid organ in blunt abdominal trauma,and splenic pseudoaneurysm rupture is associated with a high risk of mortality.Nonoperative management has become the standard t...BACKGROUND The spleen is the most commonly injured solid organ in blunt abdominal trauma,and splenic pseudoaneurysm rupture is associated with a high risk of mortality.Nonoperative management has become the standard treatment for hemodynam-ically stable patients with splenic injuries.On the other hand,delayed splenic pseudoaneurysms can develop in any patient,and at present,there are no known risk factors that may reliably predict their occurrence.Furthermore,there is a lack of consensus regarding the most appropriate strategies for monitoring and mana-ging splenic injuries,especially lower-grade(I-III).AIM To determine the predictors of pseudo-aneurysm formation following splenic injury and develop follow-up strategies for early detection of pseudoaneurysms.METHODS We retrospectively analyzed patients who visited the Level I Trauma Center bet-ween January 2013 and December 2022 and were diagnosed with spleen injuries after blunt abdominal trauma.RESULTS Using the American Association for the Surgery of Trauma spleen injury scale,the splenic injuries were categorized into the following order based on severity:Grade I(n=57,17.6%),grade II(n=114,35.3%),grade III(n=89,27.6%),grade IV(n=50,15.5%),and grade V(n=13,4.0%).Of a total of 323 patients,35 underwent splenectomy and 126 underwent angioembolization.19 underwent delayed angioembolization,and 5 under-went both initial and delayed angioem-bolization.In 14 patients who had undergone delayed angioembolization,no extravasation or pseudoaneurysm was observed on the initial computed tomography scan.There are no particular patient-related risk factors for the formation of a delayed splenic pseudoaneurysm,which can occur even in a grade I spleen injury or even 21 days after the injury.The mean detection time for a delayed pseudoaneurysm was 6.26±5.4(1-21,median:6,inter-quartile range:2-9)days.CONCLUSION We recommend regular follow-up computed tomography scans,including an arterial and portal venous phase,at least 1 week and 1 month after injury in any grade of blunt traumatic spleen injury for the timely detection of delayed pseudoaneurysms.展开更多
BACKGROUND Pelvic fractures(PF)with concomitant injuries are on the rise due to an increase of high-energy trauma.Increase of the elderly population with age related comorbidities further complicates the management.Ab...BACKGROUND Pelvic fractures(PF)with concomitant injuries are on the rise due to an increase of high-energy trauma.Increase of the elderly population with age related comorbidities further complicates the management.Abdominal organ injuries are kindred with PF due to the proximity to pelvic bones.Presence of contrast blush(CB)on computed tomography in patients with PF is considered a sign of active bleeding,however,its clinical significance and association with outcomes is debatable.AIM To analyze polytrauma patients with PF with a focus on the geriatric population,co-injuries and the value of contrast blush.METHODS This retrospective cohort study included 558 patients with PF admitted to level 1 trauma center(01/2017-01/2023).Analyzed variables included:Age,sex,mechanism of injury(MOI),injury severity score(ISS),Glasgow coma scale(GCS),abbreviated injury scale(AIS),co-injuries,transfusion requirements,pelvic angiography,embolization,laparotomy,orthopedic pelvic surgery,intensive care unit and hospital lengths of stay,discharge disposition and mortality.The study compared geriatric and non-geriatric patients,patients with and without CB and abdominal co-injuries.Propensity score matching was implemented in comparison groups.RESULTS PF comprised 4%of all trauma admissions.89 patients had CB.286(52%)patients had concomitant injuries including 93(17%)patients with abdominal co-injuries.Geriatric patients compared to non-geriatric had more falls as MOI,lower ISS and AIS pelvis,higher GCS,less abdominal co-injuries,similar CB and angio-embolization rates,less orthopedic pelvic surgeries,shorter lengths of stay and higher mortality.After propensity matching,orthopedic pelvic surgery rates remained lower(8%vs 19%,P<0.001),hospital length of stay shorter,and mortality higher(13%vs 4%,P<0.001)in geriatric patients.Out of 89 patients with CB,45(51%)were embolized.After propensity matching,patients with CB compared to without CB had more pelvic angiography(71%vs 12%,P<0.001),higher embolization rates(64%vs 22%,P=0.02)and comparable mortality.CONCLUSION Half of the patients with PF had concomitant co-injuries,including abdominal co-injuries in 17%.Similarly injured geriatric patients had higher mortality.Half of the patients with CB required an embolization.展开更多
Tracheal and bronchial injuries are life-threatening traumas that usually develop after traffic accidents or a fall from heights. The most common cause is motor vehicle accidents. Tracheobronchial injuries develop in ...Tracheal and bronchial injuries are life-threatening traumas that usually develop after traffic accidents or a fall from heights. The most common cause is motor vehicle accidents. Tracheobronchial injuries develop in 1%-2% of blunt thoracic traumas. The mortality rate is 30% in these patients and deaths usually occur within the first hours. Sixty five percent of surviving patients are diagnosed in later periods where complications are frequent. In conclusion, clinical evaluation and diagnostic tests should be performed immediately and carefully. In this study, a patient who developed tracheal rupture after blunt cervical and thoracic trauma was presented.展开更多
The hypersonic boundary-layer receptivity to slow acoustic waves is investigated for the Mach 6 flow over a 5-degree half-angle blunt cone with the nose radius of 5.08 mm. The plane acoustic wave interacts with the bo...The hypersonic boundary-layer receptivity to slow acoustic waves is investigated for the Mach 6 flow over a 5-degree half-angle blunt cone with the nose radius of 5.08 mm. The plane acoustic wave interacts with the bow shock, and generates all types of disturbances behind the shock, which may take various routes to generate the boundarylayer unstable mode. In this paper, two routes of receptivity are investigated in detail.One is through the disturbance in the entropy layer. The other is through the slow acoustic wave transmitted downstream the bow shock, which can excite the boundary-layer mode due to the synchronization mechanism. The results show that, for a low frequency slow acoustic wave, the latter route plays a leading role. The entropy-layer instability wave is able to excite the first mode near the neutral point, but its receptivity efficiency is much lower.展开更多
AIM: To retrospectively evaluate the preoperative diagnostic approaches and management of colonic injuries following blunt abdominal trauma. METHODS: A total of 82 patients with colonic injuries caused by blunt trauma...AIM: To retrospectively evaluate the preoperative diagnostic approaches and management of colonic injuries following blunt abdominal trauma. METHODS: A total of 82 patients with colonic injuries caused by blunt trauma between January 1992 and December 2005 were enrolled. Data were collected on clinical presentation, investigations, diagnostic methods, associated injuries, and operative management. Colonic injury-related mortality and abdominal complications were analyzed. RESULTS: Colonic injuries were caused mainly by motor vehicle accidents. Of the 82 patients, 58 (70.3%) had other associated injuries. Laparotomy was performed within 6 h after injury in 69 cases (84.1%), laparoscopy in 3 because of haemodynamic instability. The most commonly injured site was located in the transverse colon. The mean colon injury scale score was 2.8. The degree of faecal contamination was classified as mild in 18 (22.0%), moderate in 42 (51.2%), severe in 14 (17.1%), and unknown in 8 (9.8%) cases. Sixty-seven patients (81.7%) were treated with primary repair or resection and anastomosis. Faecal stream diversion was performed in 15 cases (18.3%). The overall mortality rate was 6.1%. The incidence of colonic injury- related abdominal complications was 20.7%. The only independent predictor of complications was the degree of peritoneal faecal contamination (P = 0.02). CONCLUSION: Colonic injuries following blunt trauma are especially important because of the severity and complexity of associated injuries. A thorough physical examination and a combination of tests can be used to evaluate the indications for laparotomy. One stage management at the time of initial exploration is mostoften used for colonic injuries.展开更多
Blunt diaphragmatic lesions (BDL) are uncommon in trauma patients, but they should be promptly recognized as a delayed diagnosis increases morbidity and mortality. It is well known that BDL are often overlooked at ini...Blunt diaphragmatic lesions (BDL) are uncommon in trauma patients, but they should be promptly recognized as a delayed diagnosis increases morbidity and mortality. It is well known that BDL are often overlooked at initial imaging, mainly because of distracting injuries to other organs. Sonography may directly depict BDL only in a minor number of cases. Chest X-ray has low sensitivity in detecting BDL and lesions can be reliably suspected only in case of intra-thoracic herniation of abdominal viscera. Thanks to its wide availability, time-effectiveness and spatial resolution, multi-detector computed tomography (CT) is the imaging modality of choice for diagnosing BDL; several direct and indirect CT signs are associated with BDL. Given its high tissue contrast resolution, magnetic resonance imaging can accurately depict BDL, but its use in an emergency setting is limited because of longer acquisition times and need for patient’s collaboration.展开更多
Blunt isolated pancreatic trauma is uncommon,accounting for 1%-4% of high impact abdominal injuries.In addition,its diagnosis can be difficult;physical signs may be poor and laboratory findings nonspecific,resulting i...Blunt isolated pancreatic trauma is uncommon,accounting for 1%-4% of high impact abdominal injuries.In addition,its diagnosis can be difficult;physical signs may be poor and laboratory findings nonspecific,resulting in delayed treatment.Preserving the spleen during distal pancreatectomy (DP) is controversial.One of the spleen's functions regards immunity;complications following splenectomy include leukocytosis,thrombocytosis,overwhelming post splenectomy sepsis and some degree of immunodeficiency.This is why many authors favor its preservation.We describe a case of a young man with an isolated pancreatic trauma due to a blunt abdominal trauma with a delayed presentation who was treated with spleen-preserving DP and we discuss the value of this procedure with reference to the literature.展开更多
Hydraulic fracture is important in unconventional oil and gas exploration.During the propagation of the hydraulic fracture,the crack tip is blunted due to the development of the process zone in the near-tip area.In th...Hydraulic fracture is important in unconventional oil and gas exploration.During the propagation of the hydraulic fracture,the crack tip is blunted due to the development of the process zone in the near-tip area.In this study,the blunting of the hydraulic fracture in polymethyl methacrylate specimens due to multi-timescale stress concentration is investigated.The ratio of the initiation toughness to the arrest toughness of the blunted hydraulic fracture is measured using both the dynamic and the static methods.Results show that a hydraulic fracture can be blunted with the time span of stress concentration from 1 ms to 600 s.It is also shown that the blunting of hydraulic fracture is a highly localized process.The morphology of the blunted crack depends on the stress distribution in the vicinity of the crack tip.展开更多
Pressure wave plays an important role in the occurrence of behind armor blunt trauma(BABT),and ballistic gelatin is widely used as a surrogate of biological tissue in the research of BABT.Comparison of pressure wave i...Pressure wave plays an important role in the occurrence of behind armor blunt trauma(BABT),and ballistic gelatin is widely used as a surrogate of biological tissue in the research of BABT.Comparison of pressure wave in the gelatin behind armor for different rifle bullets is lacking.The aim of this study was to observe dynamic changes in pressure wave induced by ballistic blunt impact on the armored gelatin block and to compare the effects of bullet type on the parameters of the transient pressure wave.The gelatin blocks protected with National Institute of Justice(NIJ) class III bulletproof armor were shot by three types of rifle bullet with the same level of impact energy.The transient pressure signals at five locations were recorded with pressure sensors and three parameters(maximum pressure,maximum pressure impulse,and the duration of the first positive phase) were determined and discussed.The results indicated that the waveform and the twin peak of transient pressure wave were not related to the bullet type.However,the values of pressure wave's parameters were significantly affected by bullet type.Additionally,the attenuation of pressure amplitude followed the similar law for the three ammunitions.These findings may be helpful to get some insight in the BABT and improve the structure design of bullet.展开更多
Stability and transition prediction of hypersonic boundary layer on a blunt cone with small nose bluntness at zero angle of attack was investigated. The nose radius of the cone is 0.5 mm; the cone half-angle is 5°...Stability and transition prediction of hypersonic boundary layer on a blunt cone with small nose bluntness at zero angle of attack was investigated. The nose radius of the cone is 0.5 mm; the cone half-angle is 5°, and the Mach number of the oncoming flow is 6. The base flow of the blunt cone was obtained by direct numerical simulation. The linear stability theory was applied for the analysis of the first mode and the second mode unstable waves under both isothermal and adiabatic wall condition, and e^N method was used for the prediction of transition location. The N factor was tentatively taken as 10, as no experimentally confirmed value was available. It is found that the wall temperature condition has a great effect on the transition location. For adiabatic wall, transition would take place more rearward than those for isothermal wall. And despite that for high Mach number flows, the maximum amplification rate of the second mode wave is far bigger than the maximum amplification rate of the first mode wave, the transition location of the boundary layer with adiabatic wall is controlled by the growth of first mode unstable waves. The methods employed in this paper are expected to be also applicable to the transition prediction for the three dimensional boundary layers on cones with angle of attack.展开更多
In a Mach 3.8 wind tunnel, both instantaneous and time-averaged flow structures of different scales around a blunt double-cone with or without supersonic film cooling were visualized via nano-tracer planar laser scatt...In a Mach 3.8 wind tunnel, both instantaneous and time-averaged flow structures of different scales around a blunt double-cone with or without supersonic film cooling were visualized via nano-tracer planar laser scattering （NPLS）, which has a high spatiotemporal resolution. Three experimental cases with different injection mass flux rates were carried out. Many typical flow structures were clearly shown, such as shock waves, expansion fans, shear layers, mixing layers, and turbulent boundary layers. The analysis of two NPLS images with an interval of 5 us revealed the temporal evolution characteristics of flow structures. With matched pressures, the laminar length of the mixing layer was longer than that in the case with a larger mass flux rate, but the full covered region was shorter. Structures like K-H （Kelvin-Helmholtz） vortices were clearly seen in both flows. Without injection, the flow was similar to the supersonic flow over a backward- facing step, and the structures were relatively simpler, and there was a longer laminar region. Large scale structures such as hairpin vortices were visualized. In addition, the results were compared in part with the schlieren images captured by others under similar conditions.展开更多
To investigate the effect of different disturbances in the upstream, we present numerical simulation of transition for a hypersonic boundary layer on a 5-degree half-angle blunt cone in a freestream with Mach number 6...To investigate the effect of different disturbances in the upstream, we present numerical simulation of transition for a hypersonic boundary layer on a 5-degree half-angle blunt cone in a freestream with Mach number 6 at 1-degree angle of attack. Evolution of small disturbances is simulated to compare with the linear stability theory （LST）, indicating that LST can provide a good prediction on the growth rate of the disturbance. The effect of different disturbances on transition is investigated. Transition onset distributions along the azimuthal direction are obtained with two groups of disturbances of different frequencies. It shows that transition onset is relevant to frequencies and amplitudes of the disturbances at the inlet, and is decided by the amplitudes of most unstable waves at the inlet. According to the characteristics of environmental disturbances in most wind tunnels, we explain why transition occurs leeside-forward and windside-aft over a circular cone at an angle of attack. Moreover, the indentation phenomenon in the transition curve on the leeward is also revealed.展开更多
Introduction:Blunt thoracic aortic injury(BTAI)is rare in elderly patients.As the population ages and life expectancy increases,the frequency of this injury will increase,while the treatment and outcomes remain unclea...Introduction:Blunt thoracic aortic injury(BTAI)is rare in elderly patients.As the population ages and life expectancy increases,the frequency of this injury will increase,while the treatment and outcomes remain unclear.Methods:We retrospectively analyzed the collected data of patients>60 years old with BTAI to investigate the mechanism of trauma;time interval from injury to diagnosis;type and timing of surgical intervention;aortic arch pattern;choice of left subclavian artery reconstruction;endograft to treat BTAI;length of the endovascular procedure;endoleaks;complications including stroke,paraplegia,and renal failure;length of hospital stay(LOS)and intensive care unit stay(L.ICUS);and 30-day mortality.Results:Five elderly trauma patients were found to have BTAI.Four(80%)were males,the cohort mean age was68 years,the major mechanism of trauma was fall injury,and the associated injury was thoracic trauma.All patients were transferred to our hospital,and emergency computed tomography angiography showed BTAI in each patient.The average time interval from injury to diagnosis was 2.7 days.Two patients suddenly showed signs of instability in their vital signs and underwent immediate endovascular repair,while 3 patients underwent delayed endovascular repair.The injury site was located in the aortic isthmus just distal to the origin of the left subclavian artery;the aortic arch pattern was II(80.0%)in 4 cases and III in 1 case(20.0%).The choice of left subclavian artery reconstruction included chimney,double chimney,prefenestration,and chimney combined with in situ fenestration.Endografts to treat BTAI included the Ankura(Lifetech Scientific,Shenzhen,China)and the C-TAG(W.L.Gore&Associates,Flagstaff,AZ USA).The length of the endovascular procedure was 75.4 min;there were no endoleaks and no complications including stroke,paraplegia,or renal failure.The average LOS was25 days,and the average L.ICUS of 2 patients was 15 days,with no 30-day mortality.Conclusion:Elderly patients with fall injury should promptly exclude BTAI.Thoracic endovascular aortic repair(TEVAR)with a left subclavian artery reconstruction technique provided good results without procedure-related or neurological complications.Because of the low incidence of this type of injury,we are unable to provide any evidence to guide the treatment option for this life-threatening condition.展开更多
The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator,obviously reducing the pe...The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator,obviously reducing the penetration efficiency of penetrator.Provided that the work of friction between projectile and target is totally transformed into the heat to melt penetrator material at its nose surface,an engineering model is established for the mass loss and nose-blunting of the ogive-nosed projectile.A dimensionless formula for the relative mass loss of projectile is obtained by introducing the dimensionless impact function I and geometry function N of the projectile.The critical value V c0of the initial striking velocity is formulated,and the mass loss of projectile tends to increase weakly nonlinearly with I/N when V0〉V c0,whilst the mass loss is proportional to the initial kinetic energy of projectile when V0展开更多
Space vehicle in atmosphere travels mostly at supersonic speed and generates a very strong bow shockwave around its blunt nose. Oblique shock and conical separated flow zone generated by a forward disk-tip spike signi...Space vehicle in atmosphere travels mostly at supersonic speed and generates a very strong bow shockwave around its blunt nose. Oblique shock and conical separated flow zone generated by a forward disk-tip spike significantly reduce the drag by reducing the high pressure area on the blunt nose. This study employs improved delayed detached eddy simulation to investigate the characteristic flow structures around a spike-tipped blunt nose at Mach number of 3 and Reynolds number（based on the blunt-body diameter） of 2.72x10;. The calculated time-averaged quantities agree well with experimental data. Characteristic frequencies in different flow regions are extracted using fast Fourier transform. It is found that two distinct instability modes exist: oscillation mode and pulsation mode. The former is related to the foreshock/turbulence interaction with nondimensional frequency at around 0.004. The latter corresponds to the interaction between turbulence and shock structures around the blunt nose, with a typical coherent structure shedding frequency at 0.092.展开更多
The computer simulation of the combustion process in blast furnace(BF) stove has been studied by using the k-ε-g turbulent diffusion flame model.The combustion process in blunt annular ceramic burner was calculated b...The computer simulation of the combustion process in blast furnace(BF) stove has been studied by using the k-ε-g turbulent diffusion flame model.The combustion process in blunt annular ceramic burner was calculated by using the software.The profiles of gas and air velocity,temperature of the combustion products,concentration of the components,and the shape and length of the flame during combustion have been researched.Compared with the original annular ceramic burner,the new design of the blunt one improves the mixing of the gas and the air significantly,and shortened the length of the flame.展开更多
For direct numerical simulation （DNS） of turbulent boundary layers, generation of an appropriate inflow condition needs to be considered. This paper proposes a method, with which the inflow condition for spatial-mod...For direct numerical simulation （DNS） of turbulent boundary layers, generation of an appropriate inflow condition needs to be considered. This paper proposes a method, with which the inflow condition for spatial-mode DNS of turbulent boundary layers on supersonic blunt cones with different Mach numbers, Reynolds numbers and wall temperature conditions can be generated. This is based only on a given instant flow field obtained by a temporal-mode DNS of a turbulent boundary layer on a flat plate. Effectiveness of the method is shown in three typical examples by comparing the results with those obtained by other methods.展开更多
基金supported by the Hong Kong Research Grants Council(Nos.15216621,15204322,25203721)the National Natural Science Foundation of China(No.12102377)。
文摘In hypersonic boundary layers,the optimal disturbance is notably caused by normalmode instabilities,such as Mack second mode.However,recent experimental and numerical efforts have demonstrated the dominance of nonmodal growth in hypersonic flows with the presence of moderate nose bluntness.In this study,resolvent analysis and parabolized stability equation analysis are performed to investigate the instabilities over a blunt-tip wedge.Main parameters include Mach number 5.9,unit Reynolds number 91.5×10~6/m,half wedge angle 5°,and nose radii ranging from 2.54 mm to 15.24 mm.Two novel growth patterns of travelling waves are identified to compete,whose nature is the intersection of the energy gain of optimal and sub-optimal disturbances.Pattern A with large spanwise wavelengths has the signature of slow energy amplification over a long distance which concentrates in the entropy layer.By contrast,pattern B with relatively small spanwise wavelengths presents rapid transient growth inside the boundary layer.A systematic study is performed on the growth/attenuation mechanism of disturbance patterns and the effects of wall temperature and nose radius.Wall cooling is found to be an alternative control strategy aimed at nonmodal instabilities.The receptivity to slow acoustic waves is considered when the effect of bluntness is studied.An estimated amplitude response favorably reproduces the reversal-like phenomenon.The lift-up/Orr mechanism analysis provides an explanation of energy growth for nonmodal responses.
基金support of the National Natural Science Foundation of China(Nos.U20A2069,12302389,12372295)the Natural Science Foundation of Fujian Province,China(No.2023J01046)。
文摘The primary Mach Reflection(MR)and pressure/heating loads on V-shaped Blunt Leading Edges(VBLEs)with variable elliptic cross-sections and conic crotches are theoretically investigated in this study.The simplified continuity method is used to forecast the shock configurations.The theoretical predictions and the numerical simulations for the Mach stem and the triple point as well as the curved shock accord well.Based on the theoretical model,an analysis of the impact of the axial ratio a/b of the cross-sectional shape and the eccentricity e of the crotch sweep path on shock structures is carried out.The shock configurations obtained from the theoretical model enable the derivation of the transition boundaries between the primary MR and the same family Regular Reflection(sRR).It is found that the increase of a/b and e can both facilitate the primary MR to sRR transition.The resulting transition and the corresponding generation of the wall pressure and heat flux are then investigated.The results indicate that higher values of the ratio a/b can significantly reduce the wall pressure and heating loads by inducing the primary MR to sRR transition.Conversely,the increase in the eccentricity e results in increased loads,despite causing the same transition.
基金the National Natural Science Foundation of China(Nos.52171316 and 51479116)。
文摘Vortex-induced vibration of hydrofoils is concerned with structural safety and noise level in hydraulic machinery and marine engineering.The research on vibration characteristics under different operating conditions is significant.In this study,numerical simulations are conducted to investigate the vortex-induced vibration responses of an elastically suspended hydrofoil with blunt trailing edge in pitch direction.The work studies the effects of four parameters,namely the structural natural frequency,mass ratio,initial attack angle,and Reynolds number on vibration characteristics,with special emphasis on frequency lock-in.Results indicate that as the structural natural frequency changes,the vibration amplitude may increase substantially within a certain frequency range,in which the vortex shedding frequency locks into the structural natural frequency,and frequency lock-in occurs.In addition,with increasing the mass ratio,the frequency range of lock-in becomes narrower,and both the upper and lower thresholds decrease.As the initial attack angle increases from 0◦to 6◦,the lock-in range gets reduced.Over the three Reynolds numbers(6×10^(5),9×10^(5),and 12×10^(5)),the lock-in range remains virtually unchanged.Moreover,for a certain structural natural frequency,modifying the mass ratio,initial attack angle,and Reynolds number could effectively suppress the vibration amplitude.
文摘BACKGROUND The spleen is the most commonly injured solid organ in blunt abdominal trauma,and splenic pseudoaneurysm rupture is associated with a high risk of mortality.Nonoperative management has become the standard treatment for hemodynam-ically stable patients with splenic injuries.On the other hand,delayed splenic pseudoaneurysms can develop in any patient,and at present,there are no known risk factors that may reliably predict their occurrence.Furthermore,there is a lack of consensus regarding the most appropriate strategies for monitoring and mana-ging splenic injuries,especially lower-grade(I-III).AIM To determine the predictors of pseudo-aneurysm formation following splenic injury and develop follow-up strategies for early detection of pseudoaneurysms.METHODS We retrospectively analyzed patients who visited the Level I Trauma Center bet-ween January 2013 and December 2022 and were diagnosed with spleen injuries after blunt abdominal trauma.RESULTS Using the American Association for the Surgery of Trauma spleen injury scale,the splenic injuries were categorized into the following order based on severity:Grade I(n=57,17.6%),grade II(n=114,35.3%),grade III(n=89,27.6%),grade IV(n=50,15.5%),and grade V(n=13,4.0%).Of a total of 323 patients,35 underwent splenectomy and 126 underwent angioembolization.19 underwent delayed angioembolization,and 5 under-went both initial and delayed angioem-bolization.In 14 patients who had undergone delayed angioembolization,no extravasation or pseudoaneurysm was observed on the initial computed tomography scan.There are no particular patient-related risk factors for the formation of a delayed splenic pseudoaneurysm,which can occur even in a grade I spleen injury or even 21 days after the injury.The mean detection time for a delayed pseudoaneurysm was 6.26±5.4(1-21,median:6,inter-quartile range:2-9)days.CONCLUSION We recommend regular follow-up computed tomography scans,including an arterial and portal venous phase,at least 1 week and 1 month after injury in any grade of blunt traumatic spleen injury for the timely detection of delayed pseudoaneurysms.
文摘BACKGROUND Pelvic fractures(PF)with concomitant injuries are on the rise due to an increase of high-energy trauma.Increase of the elderly population with age related comorbidities further complicates the management.Abdominal organ injuries are kindred with PF due to the proximity to pelvic bones.Presence of contrast blush(CB)on computed tomography in patients with PF is considered a sign of active bleeding,however,its clinical significance and association with outcomes is debatable.AIM To analyze polytrauma patients with PF with a focus on the geriatric population,co-injuries and the value of contrast blush.METHODS This retrospective cohort study included 558 patients with PF admitted to level 1 trauma center(01/2017-01/2023).Analyzed variables included:Age,sex,mechanism of injury(MOI),injury severity score(ISS),Glasgow coma scale(GCS),abbreviated injury scale(AIS),co-injuries,transfusion requirements,pelvic angiography,embolization,laparotomy,orthopedic pelvic surgery,intensive care unit and hospital lengths of stay,discharge disposition and mortality.The study compared geriatric and non-geriatric patients,patients with and without CB and abdominal co-injuries.Propensity score matching was implemented in comparison groups.RESULTS PF comprised 4%of all trauma admissions.89 patients had CB.286(52%)patients had concomitant injuries including 93(17%)patients with abdominal co-injuries.Geriatric patients compared to non-geriatric had more falls as MOI,lower ISS and AIS pelvis,higher GCS,less abdominal co-injuries,similar CB and angio-embolization rates,less orthopedic pelvic surgeries,shorter lengths of stay and higher mortality.After propensity matching,orthopedic pelvic surgery rates remained lower(8%vs 19%,P<0.001),hospital length of stay shorter,and mortality higher(13%vs 4%,P<0.001)in geriatric patients.Out of 89 patients with CB,45(51%)were embolized.After propensity matching,patients with CB compared to without CB had more pelvic angiography(71%vs 12%,P<0.001),higher embolization rates(64%vs 22%,P=0.02)and comparable mortality.CONCLUSION Half of the patients with PF had concomitant co-injuries,including abdominal co-injuries in 17%.Similarly injured geriatric patients had higher mortality.Half of the patients with CB required an embolization.
文摘Tracheal and bronchial injuries are life-threatening traumas that usually develop after traffic accidents or a fall from heights. The most common cause is motor vehicle accidents. Tracheobronchial injuries develop in 1%-2% of blunt thoracic traumas. The mortality rate is 30% in these patients and deaths usually occur within the first hours. Sixty five percent of surviving patients are diagnosed in later periods where complications are frequent. In conclusion, clinical evaluation and diagnostic tests should be performed immediately and carefully. In this study, a patient who developed tracheal rupture after blunt cervical and thoracic trauma was presented.
基金Project supported by the National Natural Science Foundation of China(Nos.11472188 and11332007)the National Key Research and Development Program of China(No.2016YFA0401200)
文摘The hypersonic boundary-layer receptivity to slow acoustic waves is investigated for the Mach 6 flow over a 5-degree half-angle blunt cone with the nose radius of 5.08 mm. The plane acoustic wave interacts with the bow shock, and generates all types of disturbances behind the shock, which may take various routes to generate the boundarylayer unstable mode. In this paper, two routes of receptivity are investigated in detail.One is through the disturbance in the entropy layer. The other is through the slow acoustic wave transmitted downstream the bow shock, which can excite the boundary-layer mode due to the synchronization mechanism. The results show that, for a low frequency slow acoustic wave, the latter route plays a leading role. The entropy-layer instability wave is able to excite the first mode near the neutral point, but its receptivity efficiency is much lower.
文摘AIM: To retrospectively evaluate the preoperative diagnostic approaches and management of colonic injuries following blunt abdominal trauma. METHODS: A total of 82 patients with colonic injuries caused by blunt trauma between January 1992 and December 2005 were enrolled. Data were collected on clinical presentation, investigations, diagnostic methods, associated injuries, and operative management. Colonic injury-related mortality and abdominal complications were analyzed. RESULTS: Colonic injuries were caused mainly by motor vehicle accidents. Of the 82 patients, 58 (70.3%) had other associated injuries. Laparotomy was performed within 6 h after injury in 69 cases (84.1%), laparoscopy in 3 because of haemodynamic instability. The most commonly injured site was located in the transverse colon. The mean colon injury scale score was 2.8. The degree of faecal contamination was classified as mild in 18 (22.0%), moderate in 42 (51.2%), severe in 14 (17.1%), and unknown in 8 (9.8%) cases. Sixty-seven patients (81.7%) were treated with primary repair or resection and anastomosis. Faecal stream diversion was performed in 15 cases (18.3%). The overall mortality rate was 6.1%. The incidence of colonic injury- related abdominal complications was 20.7%. The only independent predictor of complications was the degree of peritoneal faecal contamination (P = 0.02). CONCLUSION: Colonic injuries following blunt trauma are especially important because of the severity and complexity of associated injuries. A thorough physical examination and a combination of tests can be used to evaluate the indications for laparotomy. One stage management at the time of initial exploration is mostoften used for colonic injuries.
文摘Blunt diaphragmatic lesions (BDL) are uncommon in trauma patients, but they should be promptly recognized as a delayed diagnosis increases morbidity and mortality. It is well known that BDL are often overlooked at initial imaging, mainly because of distracting injuries to other organs. Sonography may directly depict BDL only in a minor number of cases. Chest X-ray has low sensitivity in detecting BDL and lesions can be reliably suspected only in case of intra-thoracic herniation of abdominal viscera. Thanks to its wide availability, time-effectiveness and spatial resolution, multi-detector computed tomography (CT) is the imaging modality of choice for diagnosing BDL; several direct and indirect CT signs are associated with BDL. Given its high tissue contrast resolution, magnetic resonance imaging can accurately depict BDL, but its use in an emergency setting is limited because of longer acquisition times and need for patient’s collaboration.
文摘Blunt isolated pancreatic trauma is uncommon,accounting for 1%-4% of high impact abdominal injuries.In addition,its diagnosis can be difficult;physical signs may be poor and laboratory findings nonspecific,resulting in delayed treatment.Preserving the spleen during distal pancreatectomy (DP) is controversial.One of the spleen's functions regards immunity;complications following splenectomy include leukocytosis,thrombocytosis,overwhelming post splenectomy sepsis and some degree of immunodeficiency.This is why many authors favor its preservation.We describe a case of a young man with an isolated pancreatic trauma due to a blunt abdominal trauma with a delayed presentation who was treated with spleen-preserving DP and we discuss the value of this procedure with reference to the literature.
基金the support from the China National Science and Technology Major Project"Changning-Weiyuan shale gas development demonstration project"(2016ZX05062)the support from the China National Petroleum Corporation:"Research on Influencing Factors of Gas Hydrate Sand Production and Experimental Design"(No.CPETQ201921)。
文摘Hydraulic fracture is important in unconventional oil and gas exploration.During the propagation of the hydraulic fracture,the crack tip is blunted due to the development of the process zone in the near-tip area.In this study,the blunting of the hydraulic fracture in polymethyl methacrylate specimens due to multi-timescale stress concentration is investigated.The ratio of the initiation toughness to the arrest toughness of the blunted hydraulic fracture is measured using both the dynamic and the static methods.Results show that a hydraulic fracture can be blunted with the time span of stress concentration from 1 ms to 600 s.It is also shown that the blunting of hydraulic fracture is a highly localized process.The morphology of the blunted crack depends on the stress distribution in the vicinity of the crack tip.
基金supported by the National Basic Scientific Research Project(Grant NO.JCKYS2019209C001)National Key Research and Development Program of China(Grant NO.2017YFC0822301&Grant NO.2018YFC0807206)National Natural Science Foundation of China(Grant NO.11772303)。
文摘Pressure wave plays an important role in the occurrence of behind armor blunt trauma(BABT),and ballistic gelatin is widely used as a surrogate of biological tissue in the research of BABT.Comparison of pressure wave in the gelatin behind armor for different rifle bullets is lacking.The aim of this study was to observe dynamic changes in pressure wave induced by ballistic blunt impact on the armored gelatin block and to compare the effects of bullet type on the parameters of the transient pressure wave.The gelatin blocks protected with National Institute of Justice(NIJ) class III bulletproof armor were shot by three types of rifle bullet with the same level of impact energy.The transient pressure signals at five locations were recorded with pressure sensors and three parameters(maximum pressure,maximum pressure impulse,and the duration of the first positive phase) were determined and discussed.The results indicated that the waveform and the twin peak of transient pressure wave were not related to the bullet type.However,the values of pressure wave's parameters were significantly affected by bullet type.Additionally,the attenuation of pressure amplitude followed the similar law for the three ammunitions.These findings may be helpful to get some insight in the BABT and improve the structure design of bullet.
基金Project supported by the National Natural Science Foundation of China (No.10632050)the Science Foundation of Liu-Hui Center of Applied Mathematics of Nankai University and Tianjin University.
文摘Stability and transition prediction of hypersonic boundary layer on a blunt cone with small nose bluntness at zero angle of attack was investigated. The nose radius of the cone is 0.5 mm; the cone half-angle is 5°, and the Mach number of the oncoming flow is 6. The base flow of the blunt cone was obtained by direct numerical simulation. The linear stability theory was applied for the analysis of the first mode and the second mode unstable waves under both isothermal and adiabatic wall condition, and e^N method was used for the prediction of transition location. The N factor was tentatively taken as 10, as no experimentally confirmed value was available. It is found that the wall temperature condition has a great effect on the transition location. For adiabatic wall, transition would take place more rearward than those for isothermal wall. And despite that for high Mach number flows, the maximum amplification rate of the second mode wave is far bigger than the maximum amplification rate of the first mode wave, the transition location of the boundary layer with adiabatic wall is controlled by the growth of first mode unstable waves. The methods employed in this paper are expected to be also applicable to the transition prediction for the three dimensional boundary layers on cones with angle of attack.
基金Project supported by the National Basic Research Program of China (Grant No. 2009 CB724100)the National Natural Science Foundation of China (Grant No. 11172326)
文摘In a Mach 3.8 wind tunnel, both instantaneous and time-averaged flow structures of different scales around a blunt double-cone with or without supersonic film cooling were visualized via nano-tracer planar laser scattering （NPLS）, which has a high spatiotemporal resolution. Three experimental cases with different injection mass flux rates were carried out. Many typical flow structures were clearly shown, such as shock waves, expansion fans, shear layers, mixing layers, and turbulent boundary layers. The analysis of two NPLS images with an interval of 5 us revealed the temporal evolution characteristics of flow structures. With matched pressures, the laminar length of the mixing layer was longer than that in the case with a larger mass flux rate, but the full covered region was shorter. Structures like K-H （Kelvin-Helmholtz） vortices were clearly seen in both flows. Without injection, the flow was similar to the supersonic flow over a backward- facing step, and the structures were relatively simpler, and there was a longer laminar region. Large scale structures such as hairpin vortices were visualized. In addition, the results were compared in part with the schlieren images captured by others under similar conditions.
基金Project supported by the National Natural Science Foundation of China (Nos. 90716007 and 10632050)the National Natural Science Foundation of China for Distinguished Young Scholars (No. 10802058)the Specialized Research Fund for the Doctoral Program of Higher Education (No. 200800561087)
文摘To investigate the effect of different disturbances in the upstream, we present numerical simulation of transition for a hypersonic boundary layer on a 5-degree half-angle blunt cone in a freestream with Mach number 6 at 1-degree angle of attack. Evolution of small disturbances is simulated to compare with the linear stability theory （LST）, indicating that LST can provide a good prediction on the growth rate of the disturbance. The effect of different disturbances on transition is investigated. Transition onset distributions along the azimuthal direction are obtained with two groups of disturbances of different frequencies. It shows that transition onset is relevant to frequencies and amplitudes of the disturbances at the inlet, and is decided by the amplitudes of most unstable waves at the inlet. According to the characteristics of environmental disturbances in most wind tunnels, we explain why transition occurs leeside-forward and windside-aft over a circular cone at an angle of attack. Moreover, the indentation phenomenon in the transition curve on the leeward is also revealed.
文摘Introduction:Blunt thoracic aortic injury(BTAI)is rare in elderly patients.As the population ages and life expectancy increases,the frequency of this injury will increase,while the treatment and outcomes remain unclear.Methods:We retrospectively analyzed the collected data of patients>60 years old with BTAI to investigate the mechanism of trauma;time interval from injury to diagnosis;type and timing of surgical intervention;aortic arch pattern;choice of left subclavian artery reconstruction;endograft to treat BTAI;length of the endovascular procedure;endoleaks;complications including stroke,paraplegia,and renal failure;length of hospital stay(LOS)and intensive care unit stay(L.ICUS);and 30-day mortality.Results:Five elderly trauma patients were found to have BTAI.Four(80%)were males,the cohort mean age was68 years,the major mechanism of trauma was fall injury,and the associated injury was thoracic trauma.All patients were transferred to our hospital,and emergency computed tomography angiography showed BTAI in each patient.The average time interval from injury to diagnosis was 2.7 days.Two patients suddenly showed signs of instability in their vital signs and underwent immediate endovascular repair,while 3 patients underwent delayed endovascular repair.The injury site was located in the aortic isthmus just distal to the origin of the left subclavian artery;the aortic arch pattern was II(80.0%)in 4 cases and III in 1 case(20.0%).The choice of left subclavian artery reconstruction included chimney,double chimney,prefenestration,and chimney combined with in situ fenestration.Endografts to treat BTAI included the Ankura(Lifetech Scientific,Shenzhen,China)and the C-TAG(W.L.Gore&Associates,Flagstaff,AZ USA).The length of the endovascular procedure was 75.4 min;there were no endoleaks and no complications including stroke,paraplegia,or renal failure.The average LOS was25 days,and the average L.ICUS of 2 patients was 15 days,with no 30-day mortality.Conclusion:Elderly patients with fall injury should promptly exclude BTAI.Thoracic endovascular aortic repair(TEVAR)with a left subclavian artery reconstruction technique provided good results without procedure-related or neurological complications.Because of the low incidence of this type of injury,we are unable to provide any evidence to guide the treatment option for this life-threatening condition.
基金supported by the National Outstanding Young Scientists Foundation of China(11225213)the Funds for Creative Research Groups of China(51321064)the National Natural Science Foundation of China(11172282 and 51378015)
文摘The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator,obviously reducing the penetration efficiency of penetrator.Provided that the work of friction between projectile and target is totally transformed into the heat to melt penetrator material at its nose surface,an engineering model is established for the mass loss and nose-blunting of the ogive-nosed projectile.A dimensionless formula for the relative mass loss of projectile is obtained by introducing the dimensionless impact function I and geometry function N of the projectile.The critical value V c0of the initial striking velocity is formulated,and the mass loss of projectile tends to increase weakly nonlinearly with I/N when V0〉V c0,whilst the mass loss is proportional to the initial kinetic energy of projectile when V0
基金funded by the National Natural Science Foundation of China(Nos.11572177,11572176,51376106 and 11272183)the Tsinghua University Initiative Scientific Research Program of China(No.2014z21020)
文摘Space vehicle in atmosphere travels mostly at supersonic speed and generates a very strong bow shockwave around its blunt nose. Oblique shock and conical separated flow zone generated by a forward disk-tip spike significantly reduce the drag by reducing the high pressure area on the blunt nose. This study employs improved delayed detached eddy simulation to investigate the characteristic flow structures around a spike-tipped blunt nose at Mach number of 3 and Reynolds number（based on the blunt-body diameter） of 2.72x10;. The calculated time-averaged quantities agree well with experimental data. Characteristic frequencies in different flow regions are extracted using fast Fourier transform. It is found that two distinct instability modes exist: oscillation mode and pulsation mode. The former is related to the foreshock/turbulence interaction with nondimensional frequency at around 0.004. The latter corresponds to the interaction between turbulence and shock structures around the blunt nose, with a typical coherent structure shedding frequency at 0.092.
基金Item Sponsored by National Natural Science Foundation(50104001)Science and Technology Tackle Key Foundation of Inner Mongolia(980307-4)
文摘The computer simulation of the combustion process in blast furnace(BF) stove has been studied by using the k-ε-g turbulent diffusion flame model.The combustion process in blunt annular ceramic burner was calculated by using the software.The profiles of gas and air velocity,temperature of the combustion products,concentration of the components,and the shape and length of the flame during combustion have been researched.Compared with the original annular ceramic burner,the new design of the blunt one improves the mixing of the gas and the air significantly,and shortened the length of the flame.
基金the National Natural Science Foundation of China(Nos.10632050,90716007)the Special Foundation for the Authors of National Excellent Doctoral Dissertations(No.200328)
文摘For direct numerical simulation （DNS） of turbulent boundary layers, generation of an appropriate inflow condition needs to be considered. This paper proposes a method, with which the inflow condition for spatial-mode DNS of turbulent boundary layers on supersonic blunt cones with different Mach numbers, Reynolds numbers and wall temperature conditions can be generated. This is based only on a given instant flow field obtained by a temporal-mode DNS of a turbulent boundary layer on a flat plate. Effectiveness of the method is shown in three typical examples by comparing the results with those obtained by other methods.
