Throat Cross-sectional Area Research Articles

Performance analysis of pulse detonation ramjet

Abstract A Pulse Detonation Ramjet (PDR) performance evaluation model is established based on the component-based method. The influence law of working parameters of pulse detonation combustor (PDC), PDR geometry parameters, flight speed and altitude on the performance is analyzed. Results are as follows. (1) With the increase of the equivalent ratio, the PDR specific thrust first increases and then decreases, reaching a maximum value around 1.2, but the fuel specific impulse always decreases; (2) The change of inlet throat cross-sectional area has little effect on specific thrust and fuel specific impulse, but the increase of nozzle throat cross-sectional area will have a negative effect; (3) PDR specific thrust and fuel specific impulse increase first and then decrease with the increase of flight Mach number and altitude; (4) Compared with a ramjet engine, the advantage range of PDR can reach 18.04 %, but gradually decreases with the increase of Mach number.

Simulation study of key cross-sectional area dimensions of CO2 ejector on performance

In this paper, based on the homogeneous equilibrium model, the effects of nozzle inlet cross-sectional area, nozzle throat cross-sectional area, pre-mixing chamber cross-sectional area, mixing chamber cross-sectional area, and diffusion chamber outlet cross-sectional area on the performance of the ejector of a CO2 transcritical refrigeration system are analyzed by using Ansys Fluent. The simulation results show that the primary flow rate of the ejector is sensitive only to the nozzle throat cross-sectional area, while the entrainment ratio is strongly influenced by the nozzle throat and the mixing chamber cross-sectional area, and there is an optimum value. The nozzle inlet cross-sectional area has no significant effect on the performance of the ejector. The pre-mixing and diffusion chamber outlet cross-sectional areas do not have a significant effect on the performance within a limited range, but deviating too much from the optimum value can also lead to degradation of ejector performance.

Experimental and comprehensive investigation of second throat diffuser area effect on ground test of a thrust optimized parabolic nozzle with different expansion ratios

This research examines the allowable second throat cross-sectional area of exhaust diffuser in ground tests of a thrust-optimized parabolic nozzle with different expansion ratios. First, theoretical methods used to determine the minimum second throat area and the minimum starting pressure of the exhaust diffuser have been reviewed. Next, the results of small-scale experimental tests with compressed air at diffuser inlet area to second throat area ratios (Ad/Ast) of 1.6, 1.7, 1.8, 1.85, 1.9, and 2 have been presented. To describe the physical phenomena during the start and breakdown conditions, numerical simulation of the flow has been used. The results reveal that with 11% narrowing of the second throat from area ratio 1.6 to 1.8 at all nozzle expansion ratios (34.7–65), the minimum starting pressure has grown by 7–9%. Examination of the further narrowing of the second throat up to area ratio 1.85 indicates that due to temporary flow choking in the second throat, the starting pressure has grown by up to 40%. Also, at diffuser area ratios 1.9 and above, due to severe flow choking in the second throat, the diffuser never starts. Present examinations show that with a large increase in the diffuser area ratio parameter, the nozzle pressure at which the shock pattern transition occurs in the nozzle does not change significantly. Also, diffuser breakdown pressure in the test of nozzles with different expansion ratios has shown very little dependence on the diffuser area ratio parameter. Our examinations indicate that the maximum permissible area ratio reaches the upper limit of 1.8, which is very different from the values calculated by conventional theoretical methods. Further, in this research, it has been shown that the suitable correction factor in estimating the minimum starting pressure with normal shock method in the second throat has lied within 1.4–1.7. The results indicate that the correction factor has heavily depended on the diffuser area ratio parameter. Nevertheless, this factor falls within a close range using a constant diffuser area ratio in testing of a thrust optimized parabolic nozzle with various expansion ratios. Thus, for a simpler application, the area ratio-dependent mean and maximum correction factors have been introduced which have maximum error of 3.2 and 5.6%, respectively.

Numerical Study of Water-air Ejector using Mixture and Two-phase Models

In this research, steady-state Mixture and Eulerian-Eulerian method for liquid-gas parallel flow ejector were examined. The simulation demonstrated that the Mixture model simulation represents better and efficient. The Eulerian-Eulerian model needed longer computational time and had a complexity to achieve the optimal convergence. However, both methods' performances were shown slightly similar. The models indicated a difference of about 6% in the flow rate ratio, their pressure diagrams nearly coincide, and their velocity parameter varies by 7% by comparing to the existing experimental data. Additionally, the Mixture model results appropriately conformed much better to the experimental data. So, the Mixture model was chosen for futher parametric study. Simulation results indicated that the flow rate ratio decreases by increasing the throat's cross-sectional area, and the flow rate ratio increases by increasing the nozzle's cross-sectional area. In this regard, e.g., the flow rate ratio of ejector by increasing pressure from 70 to 80 kPa, the air inlet increases up to 94%, and by increasing ejector outlet pressure, the flow rate ratio reduces such that no suction can be observed at 160 kPa. Consequently, at 150 kPa pressure ratio, the flow rate ratio was reduced by almost 100%.

COMPARATIVE STUDY OF SUPERSONIC NOZZLES

In this experiment, comparative flow analysis of two different nozzles has been performed. The analysis has been performed according to the shape of the nozzles by keeping the same input parameters. The experiment has been carried out in two preliminary steps. First one includes modeling and CFD analysis and the later part is about comparing their different properties. For this analysis, two dimensional axisymmetric nozzle geometries were drawn in Solid Works and CFD analysis is done using Fluent. The basic difference between these two nozzle geometries is their outlet divergence angle, whereas the inlet crosssectional area, throat cross-sectional area and nozzle length are exactly same. These two nozzle geometries were drawn having outlet divergence angle 10° and 20° respectively. Velocity, pressure and temperature distribution on both nozzles have been studied to take the final decision. From analysis, it is clearly observed that the nozzle having outlet divergence angle 20° gives higher exit velocity with Mach number of 5.62 whereas the nozzle with outlet divergence angle 10° gives an exit velocity with Mach number of 4.31. Besides, lower temperature distribution and lower pressure distribution were observed in the nozzle with outlet divergence angle 20° throughout the expansion zone and nozzle with outlet divergence angle 10° exhibits higher temperature and pressure throughout the expansion zone. As the nozzle with divergence angle 20° gives higher exit velocity, it is the better one between these two nozzles.

Investigation of Rocket Exhaust Diffusers for Altitude Simulation

The design and operational parameters of rocket exhaust diffusers equipped to simulate high-altitude rocket performance on the ground were investigated and characterized using a comprehensive approach (theoretical, numerical, and experimental). The physical model of concern includes a rocket motor, a vacuum chamber, and a diffuser, which have axisymmetric configurations. Further, the operational characteristics of a rocket exhaust diffuserwereanalyzed froma flowdevelopmentpointof view.Emphasiswasplacedondetailed flowstructure inthe diffuser, to observe the pressure oscillation in both the vacuum chamber and diffuser, which determines the minimum rocket-motor pressure required to start the diffuser. Numerical simulations were compared with experimental data on startup and in operational conditions to understand the effects of major design parameters, including the area ratio of diffuser to rocket-motor nozzle throat, the rocket-motor pressure, and the vacuumchamber size. Nomenclature Ad = inner cross-sectional area of diffuser Ade = exit cross-sectional area of diffuser Ae = exit cross-sectional area of rocket nozzle At = throat cross-sectional area of rocket nozzle

Numerical investigation on performance of the adjustable ejector

A numerical study on the performance of an adjustable ejector was presented. An axial spindle extending into the nozzle was used to change the throat area of the nozzle to make the ejector adjustable. The re-normalization group (RNG) k-epsilon model reconciled better with experimental measurements than other two turbulence models and was utilized to simulate the flow inside the adjustable ejector. The numerical results indicated that, at the same certain motive and suction operating conditions, the adjustable ejector had higher entrainment ratio and lower discharge pressure. The existence of spindle diminishes the nozzle throat cross-sectional area; as a result, the motive flow rate was reduced. These characteristics of the adjustable ejector provided potential for more economical design and operation. Copyright The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org, Oxford University Press.

Analytical Model of Valveless Micropumps

The flow driven by a valveless micropump with a single cylindrical pump chamber and two diffuser/nozzle elements is studied theoretically using a 1-D model. The pump cavity is driven at an angular frequency omega so that its volume oscillates with an amplitude V m. The presence of diffuser/nozzle elements with pressure-drop coefficients zeta+, zeta- (> zeta +) and throat cross-sectional area A 1 creates a rectified mean flow. In the absence of frictional forces the maximum mean volume flux (with zero pressure head) is Q 0 where Q 0/V momega = (zeta- - zeta+)pi/16(zeta-+ zeta+), while the maximum pressure that can be overcome is DeltaP max where DeltaP max A 1 2/V m 2 omega2 = (zeta- - zeta+)/16. These analytical results agree with numerical calculations for the coupled system of equations and compare well with the experimental results of Stemme and Stemme.

Hydrodynamics and mass transfer characteristics of gas–liquid ejectors

In the present work, experimental investigations have been carried out on ejectors employing air as a motive fluid and water as the entrained fluid. A semi-empirical model has been developed to predict the liquid entrainment rate taking into account: (i) the compressible nature of air, (ii) pressure drop for two-phase flow and (iii) losses due to changes in cross sectional area. The effects of gas velocity, liquid level in the suction chamber, nozzle diameter and throat diameter on the liquid entrainment, entrainment ratio (L/G), pressure drop, gas hold-up, mass transfer coefficient and interfacial area have been investigated. The liquid entrainment rate increases with the increased liquid level in the suction chamber and with the increase in gas velocity. The ratio of throat cross sectional area to the nozzle cross sectional area (area ratio) was found to be a critical parameter. These results have been explained on the basis of pressure profiles of ejector (along the centre line of the ejector). The liquid entrainment rate predicted from the semi-empirical model is in good agreement with the experimental values. The mass transfer coefficient and interfacial area increase with increase in gas velocity. Correlations have been proposed to estimate the fractional gas hold-up, mass transfer coefficient and interfacial area in the ejectors.

Hydrodynamic Characteristics of Gas–Liquid Ejectors

In the present work, experimental investigations have been carried out on ejectors employing gas (air) as a motive fluid and liquid (water) as the entrained fluid. A semi-empirical model has been developed to predict the liquid entrainment rate taking into account, (1) the compressible nature of air, (2) pressure drop for two phase flow and (3) losses due to changes in cross sectional area. The effects of gas velocity, liquid level in the suction chamber, nozzle diameter, throat height and throat diameter on the liquid entrainment, entrainment ratio and pressure drop have been investigated. It has been observed that the liquid entrainment rate increases with an increase in the liquid level in the suction chamber. It was also found to increase with an increase in the gas velocity. The ratio of throat cross-sectional area to the nozzle cross-sectional area (area ratio) was found to be a critical parameter. The results have been explained on the basis of pressure profiles. The values of liquid entrainment rate predicted from the semi-empirical model were found to be in good agreement with the experimental measurements.

화학레이저 구동용 이젝터 시스템 개발 (I) - 화학레이저 구동용 초음속 이젝터 설계 변수 연구 -

It is essential to operate chemical lasers with supersonic ejector system as the laser output power goes up. In this research, ejector design parameter study was carried out for optimal ejector design through understanding the ejector characteristics and design requirements for chemical lasers operating. Designed ejector was 3D annular type with 2^nd_throat geometry and pressurized air was used for primary flow. Ejector design was carried out with two steps, quasi-ID gas dynamics was used for first design and commercial code was used to verify the first design. In this study, to get the effect of ejector geometry on its performance, three cases of primary nozzle area ratio and 2^nd_throat cross sectional area and two cases of 2^nd-throat L/D ratio experiments were carried out. Primary and secondary pressures were measured to get the mass flow rate ratio, minimum secondary pressure, ejector starting pressure and un starting pressure at every case. In the result, better performance than design level was shown and optimal ejector design method for chemical lasers was obtained.

A numerical design study of the valveless diffuser pump using a lumped-mass model

This paper presents a lumped-mass model especially developed for valveless diffuser pumps. It is implemented using MATLAB. The model is tested for different previously reported valveless diffuser pumps and shows good agreement with the experimental results. The model predicts the flow-pressure characteristics for different excitation levels. The model makes it possible to study flows and pressures inside the pump. The simulations show that the maximum excitation level for the valveless diffuser pump is probably limited by low chamber pressure. Modified designs are tested and it is shown that a pump with two serially connected pump chambers working in anti-phase is advantageous compared with a single chamber pump for both the maximum volume flow and maximum pump pressure. The simulations also indicate that scaling down the diffuser elements from an throat cross-sectional area to a throat cross-sectional area probably increases the attainable pressure head.

Analyses of recent geomorphic evolution of Gargathy Inlet, eastern shore of Virginia, U. S. A.

Gargathy Inlet is a small natural tidal inlet in the northern region of the Virginia barrier island chain. It is 100 m wide with a throat cross-sectional area of 384 m2 and an average tidal prism of 6.47×106 m3. The inside drainage system is 7.8 km long and 2.2 km wide. The main channels comprise 5.8% of the area, shallow lagoons 19.8%, andSpartina marshes 74.4% in 1970. Over the period 1851–1989 the inlet narrowed and migrated northward while maintaining a weakening downdrift offset. The nearby barrier island coastline’s rapid retreat (average rate 4.78 m/a, 138 years retreat 660 m) was accompanied by back barrier channel and lagoon filling and a decrease in intertidal water volume which was probably the main reason for the entrance narrowing. The northward migration of the inlet was related to the dredging of the Inside Passage (before 1949) and the breaching of southern Metompkin Island (since 1957) connected with the inlet system. This altered the interior tidal circulation and likely shifted northward the divide between the drainage areas of Gargathy Inlet and Metompkin Inlet. Bypassing littoral sediment from north to south, downdrift local transport reversal, and onshore welding of swash bars formed a downdrift offset. Very strong coastal storms, particularly those of 1933 and 1962, played important roles in changing inlet geometry.

Bed friction characteristics of three tidal entrances

The regimes of flow and sediment transport through a tidal entrance are contingent upon, among other factors, the temporal and spatial distributions of the shear stress at the channel bed, defined in terms of the depth-averaged velocity, a friction factor or a Manning's n and an equivalent sand bed roughness. Direct measurement of these parameters should, therefore, yield basic information on the flow and sediment transport characteristics of the entrance. Three entrances, located on the Gulf Coast of Florida, were selected for hydraulic measurements. In two of the three entrances, bed friction characteristics were derived from near-bed velocity measurements and at the third entrance the same were obtained from measured water surface slopes in the channel. The near-bed velocity profiles were found to be logarithmic, and the effect of flow inertia was found to be significant only for relatively short time periods close to slack water. In the fully rough range of flow the bed shear stress-velocity relationship was found to follow the square law with a characteristic friction factor and Manning's n for the entrance. The measured maximum friction velocity and the friction factor have been used to estimate the tidal prism—throat cross-sectional area ratio which is then compared with the same obtained from flow discharge measurements. A reasonable agreement is observed, thus attesting to the validity of the measured friction factors.

MEASUREMENT OF BED FRICTION IN TIDAL INLETS

The flow characteristics and the stability of a tidal inlet are governed, among other factors, by the channel bed friction. In order to determine the bed shear stress regime and the frictional characteristics, near-bed velocity profiles were obtained at the throat sections of two inlets, John's Pass and Blind Pass, on the Gulf Coast of Florida. A specially designed steel cage with five current meters in a vertical array was used to obtain the profiles in the bottom one meter of the flow. The profiles were found to be logarithmic but it is noted that, especially near the times of slack water, the effect of inertia becomes significant. However, during the major part of the flood or ebb flow period, frictional effects are dominant. In the fully rough regime of flow, the bed-shear stress - velocity relationship is found to follow the square law, with a constant, characteristic friction factor and Manning's n for each inlet. This friction factor is used in hydraulic formulas, based on uniform, steady open channel flow relationships, to obtain the tidal prism - throat cross-sectional area ratio, which is then compared with that obtained from flow discharge measurements. Agreements and discrepancies in the comparison are discussed. The relationship between the bed shear stress at incipient motion and the grain size at the bed is reviewed, and it is noted that the observed relationship at the two inlets does not agree with the well-known correlation of Shields for uniform sandy beds.