Frontal Air Research Articles

Comparative Mechanical Analysis between Open and Curved Frontal Air flip on Gymnastics Floor Mat

Comparative Mechanical Analysis between Open and Curved Frontal Air flip on Gymnastics Floor Mat

CFD analysis of an exceptional cyclist sprint position

A few riders have adopted a rather exceptional and more aerodynamic sprint position where the torso is held low and nearly horizontal and close to the handle bar to reduce the frontal area. The question arises how much aerodynamic benefit can be gained by such a position. This paper presents an aerodynamic analysis of both the regular and the low sprint position in comparison to three more common cycling positions. Computational fluid dynamics simulations are performed with the 3D RANS simulations and the transition SST k–ω model, validated with wind-tunnel measurements. The results are analyzed in terms of frontal area, drag coefficient, drag area, air speed and static pressure distribution, and static pressure coefficient and skin friction coefficient on the cyclist surfaces. It is shown that the drag area for the low sprint position is 24% lower than for the regular position, which renders the former 15% faster than the latter. This 24% improvement is not only the result of the 19% reduction in frontal area, but also caused by a reduction of 7% in drag coefficient due to the changed body position and the related changes in pressure distribution. Evidently, specific training is required to exert large power in the low sprint position.

Wind influence on the exterior ballistics of the bullet movement from the SVD

In the paper the author investigate the dynamics of the movement of the bullet of the cartridge LPS in the air released from the sniper rifle Dragunov. The main influence on the bullet movement in the air has the force of the frontal air resistance, the bullet’s mass and the force caused by the action of the counter wind on the bullet. It is assumed that the force of the frontal air resistance depends on the factor described the aerodynamics properties of the bullet, the cross-section of the bullet, the density of the air and the sound velocity in the air , the velocity of the accompanying or opposite wind and the bullet’s velocity. In addition, its functional relationship contain two dimensionless coefficients that have different values in supersonic and subsonic velocity of the bullet and are determined using the results of experimental studies. The action of the accompanying or opposite wind affects the value of the force of the frontal air resistance of the bullet’s movement and is taken into account through the corresponding force expression. There is a slight difference between the theoretical and experimental results of the kinematic parameters of the bullet. The value of the force caused by the action of the crosswind is proportional to the maximum area of the longitudinal section of the bullet, the air density, and the difference of the wind velocities and cross drift of the bullet, which is elevated to a certain degree. The values of the coefficient of proportionality and degree depend on the nature of the air movement – laminar or turbulent. Analyzing the results of theoretical calculations, we can state that the velocity of the cross drift of the bullet is constantly increasing; the value of the cross drift of the bullet increases according to the nonlinear law. In addition, there are significant differences between the results of theoretical and experimental studies, if the coordinate of the point of zeroing of the trajectory is greater than 700 meters. During the theoretical verification of experimental values, it was established that the value of the average velocity of its cross drift on certain sections of the bullet movement contradicts the laws of mechanics. Consequently, certain values of experimental studies, given in the shooting tables, cause distrust.

Determination of the magnitude of the frontal air resistance of the bullet, released from the machine guns PK, PKB, PKS and PKT

In a majority of works devoted to the research of the exterior ballistics of the bullet movement and missiles the rate of the missile’s form and the reference function of the frontal air is used. However, the obtained on this ground theoretical results not always qualitatively and quantitively coincided with experimental. In the work of authors an alternate approach to the study of the dynamics of the bullets and missiles movement is considered. It is widely thought that the scalar force of the frontal air resistance of the bullet movement depends on the following characteristics: its aerodynamics rate; the greatest cross-section area plane surface vertical to the velocity attitude; its movement rate; air density and the speed of sound in the air. Although it has different values of certain coefficients in cases when the bullet is moved with supersonic and subsonic velocities. Using the law of dynamics – the system of differential equation is obtained, which describe the bullet movement in the air. To determine the certain coefficients of the frontal air resistance value function we should solve the inverse problem of the particle dynamics, taking into consideration the results of the experimental investigations. Solution of the differential equation system is obtained by a numerical method and the coefficients’ value is defined by trial and error method. As an example, the bullet movement from the machine guns such as PK, PKB, PKS and PKT. The functional dependency of the bullet movement frontal air resistance value has been obtained from its velocity and the respective diagram has been created. The received theoretical values of the bullet’s velocity on certain distances were different from the results of experimental measurements within limits of less than one percent. Knowledge of the law of the value change of the frontal air resistance on the bullet movement from its velocity, air density, and speed of sound in the air allows defining the influence of change of these values on the traveltime parameters of the bullet movement. At the same time we can investigate the influence of the change of the muzzle velocity of the bullet, angle of elevation, velocity and direction of the wind on the exterior ballistics of the bullet movement. As an illustration the influence of the angle of position on the traveltime characteristics has been investigated.

Airside thermal-hydraulic characteristics for tube bank heat exchangers used to cool compressor bleed air in an aero engine

A numerical study has been carried out to investigate the airside heat transfer and pressure drop characteristics of bare tube bank and plain finned tube heat exchangers used to cool the compressor bleed air in an aero turbine engine. The exchangers use small diameter tubes (3.0 mm) with compact staggered tube layout and operate in high temperature circumstances with large temperature differences. Calculations are performed using the Realizable k-ɛ turbulence model with consideration of the air property variations caused by the air temperature and pressure changes. Calculations are implemented for 5–20 m/s frontal air velocities, 561–690 K and 0.5–1.0 MPa frontal air temperatures and pressures, which correspond to 15–30 compressor compression ratios, and 298 and 350 K tube wall temperatures. The airside thermal-hydraulic performance is evaluated using the heat transfer coefficient and pressure drop as well as their dimensionless forms - j and f factors. The results suggest that the heat transfer coefficient and pressure drop are strongly affected by the frontal air state whereas the j and f factors are less dependent on it. The effect of air property variability on j factor is limited while that on f factor is more notable.

The application of 3D reconstruction in investigating the frontal sinus drainage pathway based on computer tomography data

Objective:The aim of this study is to explore the value of 3D reconstruction technology based on computer tomography data in understanding the frontal sinus drainage pathway. Method:Three-dimensional reconstruction of DICOM data from 100 cases of sinus CT was performed by using Mimics 19.0 software. The 3D models were used to study types, the relative locations of frontal sinus and recess cells as well as the influence of the frontal sinus drainage pathway. Result:The 3D model of frontal sinus, frontal recess cells and frontal sinus drainage pathway were reconstructed successfully. Among them, the incidence of nasal cavity was 95.5% (191/200), nasal cavity was 31.5% (63/200), nasal cavity on the frontal air room was 24.5% (49/200) supra bulla cells were 54% (108/200), supra bulla frontal cells were 14.5% (29/200), supraorbital ethmoid cells were 20.5% (41/200), and the rate of frontal septal cells were 4% (8/200). It visually demonstrated the relationship between the frontal recess and the frontal sinus drainage channel. Conclusion:The 3D reconstruction technology based on computer tomography data not only helps us to understand the anatomy of the frontal sinus, the relative position of the frontal crypt and the effect on the frontal sinus drainage channel, but also provides a new method for preoperative planning and intraoperative guidance to endoscopic frontal sinus surgery.

An experimental, computational and flow visualization study on the air-side thermal and hydraulic performance of louvered fin and round tube heat exchangers

The aim of this study is to determine heat transfer and pressure drop characteristics in different louvered fin geometries for manufacturing of commercial louvered fin and round tube heat exchangers. Numerical simulations were carried out for various louver angles, louver lengths (pitches), fin pitches and frontal air velocities. The heat transfer and pressure drop characteristics of the louvered fin and round tube heat exchangers, Colburn and friction factors, were respectively normalized with Colburn and friction factors of the flat plate fin and round tube heat exchangers operating under the same conditions and they were presented as the relative Colburn factor j∗ and the relative friction factor f∗. Thermal & hydraulic performance was presented as JF∗. Temperature and local Nusselt number contours, and streamline patterns were provided to reveal the mechanisms behind the heat transfer enhancement. Among different heat exchangers for which heat transfer and pressure drop characteristics were obtained, one was chosen to manufacture a real size heat exchanger. Flow visualization studies were also conducted with a PIV system in an open water channel to determine whether the flow structure is louvered directed or not. The louvered fin heat exchanger tested in the PIV system was a five times scaled up model of the real size louvered fin heat exchanger and made from a transparent plexiglas material. PIV results were presented and evaluated based on streamlines and velocity vectors. Furthermore, a numerical analysis was performed using exactly the same dimensions and conditions of the model tested in the PIV system. The comparison between numerical and experimental results was done to validate the numerical model. Consequently, the performance of the fabricated real size heat exchanger was tested at different air velocities in a wind tunnel in a conditioned room. The experimental results were compared with numerical analyses and found to be compatible with each other. Finally, thermal and hydraulic performance of the louvered fin and round tube heat exchanger was compared with a wavy fin and round tube heat exchanger with identical size and specifications. It was found that the thermal and hydraulic performance of the louvered fin and round tube heat exchanger is higher than that of the wavy fin and round tube heat exchanger. The Colburn factor j, friction factor f and JF of the louvered fin and round tube heat exchanger are higher about 16.8–7%, 19.9–8.2% and 10–4.3% than that of the wavy fin and round tube heat exchanger depending on the Reynolds number, respectively.

Performance improvements evaluation of an automobile air conditioning system using CO2-propane mixture as a refrigerant

The main purpose of this work is to enhance the energy efficiency of CO2 automobile air conditioning system. Theoretical analysis demonstrated that the mixture of CO2 and propane can improve its performance, thus, experiments have been carried out to see effects of various CO2-propane mass fractions of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50 on the system performance at different ambient temperatures and gas cooler frontal air velocities. Experimental results show similar trends with those from the theoretical results. It has been shown that under the same compressor speed, system COP reaches highest at 60% of CO2 mass fraction, which is 29.4% higher than pure CO2 system and even achieves equal level of the R134a system, the optimum pressure and discharge temperature are reduced up to a maximum of 40% and 47 °C during the research range. Furthermore, comparison was carried out under the same cooling capacity by adjusting compressor speed for different mass fraction of CO2, results demonstrate that the use of CO2-propane mixtures yields a maximum COP rise of 22%even when cooling capacity is kept constant. A new optimum high pressure control algorithm for the transcritical CO2-propane mixture cycle has been developed based on the experimental data within a deviation of 5%.

Frontal sinus outflow tract: Multi-detector CT assessment

IntroductionKnowledge of the normal anatomical variants is critical for safe endoscopic navigation during FESS. The frontal sinus outflow tract FSOT includes the frontal infundibulum, ostium and recess respectively in the direction of the drained secretions. The original classification of Bent and Kuhn (B&K) divided the frontal infundibulum cells into four categories. Lund and Mackay scoring system (LMS) is a radiological score that offer effective evaluation of sinusitis. The aim of this work was to revise the radiological classification of frontal air cells by B&K and to correlate it with the clinic-radiological LMS scoring system. Methods and resultsThis study was carried out on 200 sides divided into two equal groups. Three types were added to the original B&K description; Type 0 (Not identified frontal cells), Combined type and Couldn't be assessed type. The percentages of each type were calculated according to modified B&K classification and correlated to LMS. ConclusionsThe main limitation of the original B&K classification system is to accurately classify frontal air cells in cases with extensive opacification of the frontal sinus (LMS 2) as well as in cases of complicating sino-nasal polyposis. Three new types are suggested to be added to the original B&K classification system.

CFD analysis of internal ventilation in high-speed human powered vehicles

When dealing with fully faired human powered vehicles (HPVs) for speed or endurance record attempts, the need for internal ventilation of the rider arises. Different solutions have been proposed in the literature and in practice by designers and builders of these bicycles. The present paper proposes an analytical approach to design the frontal air inlet according to the VO $$_{2}$$ max of the rider in speed competitions. A 3D computational fluid dynamics (CFD) model is presented to analyse the external and internal flow interaction with respect to three design parameters: the presence of wheel covers, the location of the rear vent and its geometry. The CFD results predict that the wheel covers save 23 W of aerodynamic power at 125 km/h. A secondary but significant design parameter is the rear vent position that can provide a further reduction of 11 W at 125 km/h if properly located. Finally, the effect of the rear vent geometry was below the model confidence level, resulting in a likely negligible design parameter.

Morphometric Sexual Dimorphism of Frontal Air Sinus: ACT Study

Morphometric Sexual Dimorphism of Frontal Air Sinus: ACT Study

Versatility of the Latissimus Dorsi Free Flap during the Treatment of Complex Postcraniotomy Surgical Site Infections.

Background:Some intractable cases of postcraniotomy infection, which can involve compromised skin, an open frontal air sinus, and residual epidural dead space, have been reported. In such cases, reconstructing the scalp and skull is challenging.Methods:Between 2009 and 2016, the author treated 12 patients with recalcitrant postcraniotomy surgical site infections with latissimus dorsi (LD) free flaps. The patients’ ages ranged from 37 to 79 years (mean, 63.5 years), and their underlying diseases included subarachnoid hemorrhaging (n = 5), brain tumors (n = 4), and cerebral arteriovenous malformations (n = 3).Results:The LD free flap was used for scalp reconstruction in 3 cases, scalp reconstruction and separation of the intracranial and nasal cavities in 5 cases, and the obliteration of epidural dead space in 4 cases. Debridement followed by staged cranial reconstruction was carried out in 8 cases, and single-stage cranial reconstruction was conducted in 2 cases. The bone defects of the other 2 cases, which were small, were filled with LD musculo-adipose free flaps. The postoperative local appearance of the wounds was acceptable in every case, and no complications occurred.Conclusions:The LD free flap is a versatile tool for the treatment of complex postcraniotomy surgical site infections. This vascularized muscle flap is useful for controlling local infections because of its abundant vascularity. Moreover, its variety of uses means that it can resolve several problems in cases involving complex cranial wounds.

Airside heat transfer and pressure loss characteristics of bare and finned tube heat exchangers used for aero engine cooling considering variable air properties

Numerical studies have been conducted to investigate the airside thermal-hydraulic characteristics of bare tube bank and plain finned tube heat exchangers intended for use in aero-engine cooling. The exchangers use small diameter tubes (3.0mm) with compact tube layout and operate at high temperatures with large temperature changes over the exchanger depth. Calculations are performed for frontal air velocities between 5 and 20m/s, yielding tube diameter based Reynolds numbers from 4898 to 19,592. Calculations are implemented using the Realizable k-ɛ turbulence model with consideration of the air physical property variations caused by the air temperature changes. The results show that ignorance of the air property variability leads to overestimations of both heat transfer and pressure loss, with a smaller air velocity yielding a more serious overestimation. The numerical fin efficiency agrees with the Schmidt fin efficiency within 7.0%. The plain finned tube heat exchanger is superior to the bare tube bank heat exchanger if the exchanger performance is evaluated using the heat transfer rate to pressure drop ratio.

INVESTIGATION ON HEAT TRANSFER ENHANCEMENT IN A CORRUGATED FIN-AND-TUBE COMPACT HEAT EXCHANGER

Heat transfer augmentation and pressure loss penalty in the fin-and-tube compact heat exchangers (FTCHEs) with the corrugated shape as a special form of the fin are numerically investigated to improve heat transfer performance criteria in low Reynolds numbers. The corrugated fin as the newly design of fin pattern is presented in this study. The influence of applying corrugated design adjustments on the thermal and hydraulic characteristics of air flow are analyzed on the in-line tube arrangements. The performance of air-side heat transfer and fluid flow is investigated by numerical simulation for Reynolds number ranging from Re = 400 to 800 based on the tube collar diameter, with the corresponding frontal air velocity ranging from 0.35 to 0.72 m/s. The outcomes of simulation revealed that the corrugated fin could significantly improve the heat transfer augmentation of the FTCHEs with a moderate pressure loss penalty. The computational results indicated that some eddies were developed behind the fluted domain of corrugated finwhich produce some disruptions to fluid flow and enhance heat transfer compared with plain fin. The corrugated form of fins could enhance the thermal mixing of the fluid, delay the boundary layer separation, and reduce the size of the wake and the recirculation region behind tubes compared with the conventional form of the fin at the range of Reynolds number used in this study. In addition, the results showed that the average Nusselt number for the FTCHE with corrugated fin increased by 7.05–10.0% over the baseline case and the corresponding pressure loss decreased by 5.0–6.2%.

Cooling Performance Characteristics of the Stack Thermal Management System for Fuel Cell Electric Vehicles under Actual Driving Conditions

The cooling performance of the stack radiator of a fuel cell electric vehicle was evaluated under various actual road driving conditions, such as highway and uphill travel. The thermal stability was then optimized, thereby ensuring stable operation of the stack thermal management system. The coolant inlet temperature of the radiator in the highway mode was lower than that associated with the uphill mode because the corresponding frontal air velocity was higher than obtained in the uphill mode. In both the highway and uphill modes, the coolant temperatures of the radiator, operated under actual road driving conditions, were lower than the allowable limit (80 °C); this is the maximum temperature at which stable operation of the stack thermal management system of the fuel cell electric vehicle could be maintained. Furthermore, under actual road driving conditions in uphill mode, the initial temperature difference (ITD) between the coolant temperature and air temperature of the system was higher than that associated with the highway mode; this higher ITD occurred even though the thermal load of the system in uphill mode was greater than that corresponding to the highway mode. Since the coolant inlet temperature is expected to exceed the allowable limit (80 °C) in uphill mode under higher ambient temperature with air conditioning system operation, the FEM design layout should be modified to improve the heat capacity. In addition, the overall volume of the stack cooling radiator is 52.2% higher than that of the present model and the coolant inlet temperature of the improved radiator is 22.7% lower than that of the present model.

Numerical and Experimental Research on Performance of Single-row Finned Tubes in Air Cooled Power Plants

In this paper, a new configuration of drop-shaped tube is proposed to improve the finned-tube thermo-flow performance. As the basic heat exchanger element of a Direct Air Cooled Condenser (DACC), the performance of finned tubes is very important to the optimal design of DACCs. Under turbine rated load (TRL) conditions and various frontal air velocities, the airside flow and heat transfer performance of single row flattened finned tubes and drop-shaped finned tubes are numerically investigated. The flow field, temperature field and thermo-flow characteristics are analyzed. Experimental verification and field coordination (synergy) analysis are carried out, with the simulation results agreeing well with experimental results. The performance of pressure drop, heat transfer coefficient and power consumption of these 4 Schemes are comprehensively compared and evaluated. When compared to the flattened finned tube the pressure drop of the drop-shaped Scheme 4 tube reduced by 5.9 % while the heat transfer coefficient reduced by 2.8 % at a frontal velocity of 1.8 m/s. Scheme 4 produces the best thermo-flow performance, especially at low air velocity, benefiting from a lower pressure drop and a moderate heat transfer coefficient.

Toward a more rationalized use of a special technique for repair of frontal air sinus after cerebral aneurysm surgery: The most effective technique

Abstract A craniotomy that passes through the frontal air sinus (FAS) often results in postoperative complications such as infection, cerebrospinal fluid leakage or mucocele formation. A good understanding of FAS reconstruction can decrease the morbidity rate of complications. This study describes the outcomes of treatment and establishes the most effective technique for FAS reconstruction in our institution. We enrolled 107 patients who had a bifrontal craniotomy which exposed the FAS during the operation for an anterior communicating artery (ACoA) aneurysm. Demographic data including the follow-up information were collected and analyzed. The complications after surgery were observed and described in the treatment procedure. The patency of the nasofrontal outflow tract (NFOT) was proved by removal of blood clots and bone dust by irrigation and by direct inspection under a microscope before closure of the frontal sinus mucosa with a monofilament non-absorbable 7/0 material suture. The dura was closed in a watertight fashion and an abdominal fat graft was packed into the FAS cavity. There were 33 male and 74 female patients and the mean age (range) was 64 years (32–90 years). The mean follow-up time was 13 months (1–35 months) and complications were found in only 2 patients. One patient suffered from dislocation of the fat graft and the other patient developed a surgical wound infection. At post-operation the first patient sneezed several times and the second patient suffered from trauma in the nasal area after discharge to home. Both patients were surgically treated and cured. In conclusion, FAS reconstruction from our technique is very effective for the prevention of complications after bifrontal craniotomy. Direct suturing of the frontal sinus mucosa and proving the patency of the NFOT are keys to successful treatment.

Experimental and parametric studies of a louvered fin and flat tube compact heat exchanger using computational fluid dynamics

The present study aimed to perform the parametric analysis on thermo-hydraulic performance of a compact heat exchanger using computational fluid dynamics (CFD). The analysis has been carried out at different frontal air velocities by varying the geometrical parameters such as fin pitch, transverse tube pitch, longitudinal tube pitch, louver pitch and louver angle. The air side performance of the heat exchanger has been evaluated by calculating Colburn factor (j) and Fanning friction factor (f). The comparison of CFD results with the experimental data exhibited a good agreement and the influence of various geometrical parameters for the selected range of values on the pressure drop, heat transfer coefficient and goodness factor was analyzed. The results obtained from the analysis will be very useful to optimize the louvered fin and flat tube compact heat exchanger for better thermo-hydraulic performance analysis without the need of time consuming and expensive experimentation.

Anatomical variation of middle concha and its clinical correlates: a study among patients attending North Bengal Medical College

Abstract Background and aims: Lateral nasal wall of each nasal cavity provides the final common pathway of drainage of the muco-ciliary clearance of frontal, maxillary and anterior ethmoidal air cells. Anatomical variant like Concha Bullosa may obstruct the muco­ ciliary clearance thmugh osteomeatal complex and cause rhino sinusitis. The objectives were to find out the anatomical variation of middle concha and its clinical correlates with variation of middle concha. Methods: The present study was a descriptive, hospital based cross sectional study carried out in the outpatient departments of North Bengal Medical College & Hospital among 15 years and above patients. Coronal CT scan of paranasal sinus and orbit region was done. Data was collected with the help of semi structured predesigned and pretested questionnaire. Results: Of the 44 study patients, 15.9% had Concha Bullosa, 11.36% had paradoxical middle concha. Dimensions of right and left concha were also studied. 77.3%, 59.1% and 47.7% had sneezing, rhinorrhoea and headache respectively. Conclusion: The harmony of mucociliary clearance and obstruction free osteomeatal complex is the key factor for ventilation and drainage of maxillary, fmntal and anterior ethmoidal air cells.

Cloud microphysical background for the Israel-4 cloud seeding experiment

The modest amount of rainfall in Israel occurs in winter storms that bring convective clouds from the Mediterranean Sea when the cold post frontal air interacts with its relatively warm surface. These clouds were seeded in the Israel-1 and Israel-2 cloud glaciogenic seeding experiments, which have shown statistically significant positive effect of added rainfall of at least 13% in northern Israel, whereas the Israel-3 experiment showed no added rainfall in the south. This was followed by operational seeding in the north since 1975.The lack of physical evidence for the causes of the positive effects in the north caused a lack of confidence in the statistical results and led to the Israel-4 randomized seeding experiment in northern Israel. This experiment started in the winter of 2013/14. The main difference from the previous experiments is the focus on the orographic clouds in the catchment of the Sea of Galilee. The decision to commence the experiment was partially based on evidence supporting the existence of seeding potential, which is reported here.Aircraft and satellite microphysical and dynamic measurements of the clouds document the critical roles of aerosols, especially sea spray, on cloud microstructure and precipitation forming processes. It was found that the convective clouds over sea and coastal areas are naturally seeded hygroscopically by sea spray and develop precipitation efficiently. The diminution of the large sea spray aerosols farther inland along with the increase in aerosol concentrations causes the clouds to develop precipitation more slowly. The short time available for the precipitation forming processes in super-cooled orographic clouds over the Golan Heights farthest inland represents the best glaciogenic seeding potential.