Simulation of Compressible and Incompressible Flows Through Planar and Axisymmetric Abrupt Expansions

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Ali Nouri-Borujerdi ◽  
Ardalan Shafiei Ghazani
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Pressure Loss ◽  
Incompressible Flows ◽  
Splitting Method ◽  
Expansion Ratio ◽  
Loss Coefficient ◽  
Turbulent Regime ◽  
Reattachment Length ◽  
Pressure Loss Coefficient

In this paper, compressible and incompressible flows through planar and axisymmetric sudden expansion channels are investigated numerically. Both laminar and turbulent flows are taken into consideration. Proper preconditioning in conjunction with a second-order accurate advection upstream splitting method (AUSM+-up) is employed. General equations for the loss coefficient and pressure ratio as a function of expansion ratio, Reynolds number, and the inlet Mach number are obtained. It is found that the reattachment length increases by increasing the Reynolds number. Changing the flow regime to turbulent results in a decreased reattachment length. Reattachment length increases slightly with a further increase in Reynolds number. At a given inlet Mach number, the maximum value of the ratio of the reattachment length to step height occurs at the expansion ratio of about two. Moreover, the pressure loss coefficient is a monotonic increasing function of expansion ratio and increases drastically by increasing Mach number. Increasing inlet Mach number from 0.1 to 0.2 results in an increase in pressure loss coefficient by less than 5%. However, increasing inlet Mach number from 0.4 to 0.6 results in an increase in loss coefficient by 70–100%, depending on the expansion ratio. It is revealed that increasing Reynolds number beyond a critical value results in the loss of symmetry for planar expansions. Critical Reynolds numbers change adversely to expansion ratio. The flow regains symmetry when the flow becomes turbulent. Similar bifurcating phenomena are observed beyond a certain Reynolds number in the turbulent regime.

A Study of the Fabrication and Analysis of Micro Diffuser/Nozzles

2003 ◽  
Author(s):  
Kai-Shing Yang ◽  
Ing-Young Chen ◽  
Bor-Yuan Shew ◽  
Chi-Chuan Wang
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Pressure Loss ◽  
Measured Data ◽  
Loss Coefficient ◽  
Opening Angle ◽  
Velocity Change ◽  
Pressure Loss Coefficient ◽  
Micro Nozzle ◽  
Volumetric Flowrate

In this study, an analysis of the performance of micro nozzle/diffusers is performed and fabrication of the micro nozzle/diffuser is conducted and tested. It is found that the pressure loss coefficient for the nozzle/diffuser decreases with the Reynolds number. At a given Reynolds number, the pressure loss coefficient for nozzle is higher than that of the diffuser due to considerable difference in the momentum change. For the effect of nozzle/diffuser length on the pressure loss coefficient, it is found that the influence is rather small. At a fixed volumetric flowrate, a “minimum” phenomenon of the pressure loss coefficient vs. nozzle/diffuser depth is encountered. This is related to the interactions of velocity change and friction factor. Good agreements of the measured data with the predicted results are found in this study except at a diffuser having an opening angle of 20° . It is likely that the departure of this case to the prediction is due to the separation phenomenon in a larger angle of the diffuser.

Pressure loss of gaseous flow at a micro-tube outlet

2010 ◽  
Vol 225 (3) ◽  
pp. 649-657
Author(s):  
Y Horii ◽  
Y Asako ◽  
C Hong ◽  
J Lee
Keyword(s):  
Mach Number ◽  
Atmospheric Pressure ◽  
Pressure Loss ◽  
Stagnation Pressure ◽  
Loss Coefficient ◽  
Arbitrary Lagrangian Eulerian ◽  
Gaseous Flow ◽  
Pressure Loss Coefficient ◽  
Loss Coefficients ◽  
Energy Equations

The pressure loss of gaseous flow at a micro-tube outlet was investigated numerically. The numerical methodology is based on the arbitrary Lagrangian—Eulerian (ALE) method. Axis-symmetric compressible momentum and energy equations are solved to obtain the pressure loss coefficient of gaseous flow at a micro-tube outlet. Computed tube diameters are 50, 100, and 150μm. The stagnation pressure of upper stream of the tube is chosen in such a way that the Mach number at the tube outlet ranges from 0.1 to 1.2. The ambient (back) pressure is fixed at the atmospheric pressure. The pressure loss coefficients are compared with available experimental data for a conventionally sized tube. The effects of the Mach number and the tube diameter on the pressure loss coefficient are discussed and a correlation for the pressure loss coefficient is proposed.

Laminar Pressure Loss Coefficient in Close Coupled Fittings

2006 ◽  
Author(s):  
Murthy Lakshmiraju ◽  
Jie Cui
Keyword(s):  
Reynolds Number ◽  
Pressure Loss ◽  
Total Pressure ◽  
Laminar Flows ◽  
Loss Coefficient ◽  
Piping System ◽  
Duct System ◽  
Pressure Loss Coefficient ◽  
Intermediate Distance ◽  
Loss Coefficients

Close-coupled fittings are widely used in piping system to change the direction of the fluid and to connect pipes. These fittings cause losses and these losses play a significant role in the total pressure loss in a duct system. Numerical simulations were performed using Fluent on laminar flows in a circular pipe to obtain pressure loss coefficients associated with different fittings of two elbows and three elbows. Each configuration was studied with different intermediate distances between fittings of 0, 1, 3, 5, and 10 pipe diameters. It was observed that for a Reynolds number of 100 and for an intermediate distance less than 5 pipe diameters, the pressure loss coefficient for the coupled fittings was less than that of the uncoupled fittings. While the fittings become uncoupled when the intermediate distance was greater than 5 pipe diameters. Variation of velocity along the axis of the pipe was analyzed to understand the mechanism of the pressure loss for various fitting configurations with different intermediate distances.

Analysis of microdiffuser/nozzles

2006 ◽  
Vol 220 (8) ◽  
pp. 1289-1296 ◽  
Author(s):  
K-S Yang ◽  
M-S Liu ◽  
I-Y Chen ◽  
C-C Wang
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Pressure Loss ◽  
Three Dimensional ◽  
Side Wall ◽  
Loss Coefficient ◽  
Opening Angle ◽  
Three Dimensional Model ◽  
Velocity Change ◽  
Pressure Loss Coefficient

In this study, an analysis of the performance of micronozzle/diffusers is performed and fabrication of the micronozzle/diffuser is conducted and tested. It is found that the ratio of the loss coefficient of nozzle and diffuser increases with the Reynolds number and with the opening angle. At a given Reynolds number, the pressure loss coefficient for nozzle is higher than that of the diffuser due to considerable difference in the momentum change. At a fixed volumetric flowrate, a ‘minimum’ phenomenon of the pressure loss coefficient versus nozzle/diffuser depth is encountered. This is related to the interactions of velocity change and friction factor. Good agreements of the measured data with the predicted results are found in this study except at a diffuser having an opening angle of 20°. This is because of the presence of flow separation. The departure of this case to the prediction is due to the separation phenomenon in a larger angle of the diffuser. Hence, a more complicated two- and three-dimensional model is adopted to verify this flow separation inside the diffuser. For the simulation of the two-dimensional case, asymmetry flow field is seen for low Reynolds number region, whereas this phenomenon is not seen under three-dimensional simulation due to the confinement of the side wall.

Effect of Plenum Length and Diameter on Turbulent Heat Transfer in a Downstream Tube and on Plenum-Related Pressure Losses

1981 ◽  
Vol 103 (3) ◽  
pp. 415-422 ◽  
Author(s):  
S. C. Lau ◽  
E. M. Sparrow ◽  
J. W. Ramsey
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Turbulent Regime ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient

A systematic experimental study was carried out to determine how the heat transfer characteristics of a turbulent tube flow are affected by the length and diameter of a cylindrical plenum chamber which delivers fluid to the tube. The net pressure loss due to the presence of the plenum was also measured. The experimental arrangement was such that the fluid experiences a consecutive expansion and contraction in the plenum before entering the electrically heated test section. Air was the working fluid, and the Reynolds number was varied over the range from 5,000 to 60,000. It was found that at axial stations in the upstream portion of the tube, there are substantially higher heat transfer coefficients in the presence of longer plenums. Thus, a longer plenum functions as an enhancement device. On the other hand, the plenum diameter appears to have only a minor influence in the range investigated (i.e., plenum diameters equal to three and six times the tube diameter). The fully developed Nusselt numbers are independent of the plenum length and diameter. With longer plenums in place, the thermal entrance length showed increased sensitivity to Reynolds number in the fully turbulent regime. The pressure loss coefficient, which compares the plenum-related pressure loss with the velocity head in the tube, increases more or less linearly with the plenum length. With regard to experimental technique, it was demonstrated that guard heating/cooling of the electrical bus adjacent to the tube inlet is necessary for accurate heat transfer results at low Reynolds numbers but, although desirable, is less necessary at higher Reynolds numbers.

Pressure-Loss Coefficient of 90 deg Sharp-Angled Miter Elbows

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Wameedh T. M. Al-Tameemi ◽  
Pierre Ricco
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Pressure Loss ◽  
Dynamic Pressure ◽  
Reynolds Numbers ◽  
Loss Coefficient ◽  
Straight Pipe ◽  
Pressure Loss Coefficient ◽  
Circular Pipes ◽  
Piping Systems

The pressure drop across 90deg sharp-angled miter elbows connecting straight circular pipes is studied in a bespoke experimental facility by using water and air as working fluids flowing in the range of bulk Reynolds number 500<Re<60,000. To the best of our knowledge, the dependence on the Reynolds number of the pressure drop across the miter elbow scaled by the dynamic pressure, i.e., the pressure-loss coefficient K, is reported herein for the first time. The coefficient is shown to decrease sharply with the Reynolds number up to about Re=20,000 and, at higher Reynolds numbers, to approach mildly a constant K=0.9, which is about 20% lower than the currently reported value in the literature. We quantify this relation and the dependence between K and the straight-pipe friction factor at the same Reynolds number through two new empirical correlations, which will be useful for the design of piping systems fitted with these sharp elbows. The pressure drop is also expressed in terms of the scaled equivalent length, i.e., the length of a straight pipe that would produce the same pressure drop as the elbow at the same Reynolds number.

Pressure Loss Coefficient of Impingement Cooled Leading Edge System of a Turbine Blade

1976 ◽  
Vol 98 (4) ◽  
pp. 554-556
Author(s):  
D. K. Mukherjee
Keyword(s):  
Reynolds Number ◽  
Turbine Blade ◽  
Model Test ◽  
Pressure Loss ◽  
Leading Edge ◽  
Loss Coefficient ◽  
Relative Distance ◽  
Pressure Loss Coefficient

The pressure loss coefficient of an impingement cooled system similar to that often used to cool the leading edge of a turbine blade has been determined from model test. The influence of Reynolds number in the range tested is negligible. However, the influence of relative distance of the jet holes from the surface to be cooled is very significant.

Vibration suppression investigation and parametric design of tri-axle straight heavy truck with pitch-resistant hydraulically interconnected suspension

2021 ◽  
pp. 107754632110396
Author(s):  
Fei Ding ◽  
Jie Liu ◽  
Chao Jiang ◽  
Haiping Du ◽  
Jiaxi Zhou ◽  
...  
Keyword(s):  
Surface Area ◽  
Dynamic Load ◽  
Pressure Loss ◽  
Vibration Suppression ◽  
Parametric Design ◽  
Suspension System ◽  
Loss Coefficient ◽  
The Body ◽  
Impedance Matrix ◽  
Pressure Loss Coefficient

The vibration suppression of the proposed pitch-resistant hydraulically interconnected suspension system for the tri-axle straight truck is investigated, and the vibration isolation performances are parametrically designed to achieve smaller body vibration and tire dynamic load using increased pitch stiffness and optimized pressure loss coefficient. For the hydraulic subsystem, the transfer impedance matrix method is applied to derive the impedance matrix. These hydraulic forces are incorporated into the motion equations of mechanical subsystem as external forces according to relationships between boundary flow and mechanical state vectors. In terms of the additional mode stiffness/damping and suspension performance requirements, the cylinder surface area, accumulator pressure, and damper valve’s pressure loss coefficient are comprehensively tuned with parametric design technique and modal analysis method. It is found the isolation capacity is heavily dependent on installation scheme and fluid physical parameters. Especially, the surface area can be designed for the oppositional installation to separately raise pitch stiffness without increasing bounce stiffness. The pressure loss coefficients are tuned with design of experiment approach and evaluated using all conflict indexes with normalized dimensionless evaluation factors. The obtained numerical results indicate that the proposed pitch-resistant hydraulically interconnected suspension system can significantly inhibit both the body and tire vibrations with decreased suspension deformation, and the tire dynamic load distribution among wheel stations is also improved.

The Characteristics Study of Helium-Xenon Mixture in Closed Brayton Cycle for Space Nuclear Reactor Power

2018 ◽  
Author(s):  
Xie Yang ◽  
Lei Shi
Keyword(s):  
Physical Properties ◽  
Pressure Loss ◽  
Nuclear Reactor ◽  
Reactor Power ◽  
Loss Coefficient ◽  
Working Fluid ◽  
System Efficiency ◽  
Pressure Loss Coefficient ◽  
Molar Weight ◽  
Xenon Mixture

Differing from the adoption of helium as working fluid of closed Brayton cycle (CBC) for terrestrial high temperature gas cooled reactor (HTGR) power plants, helium-xenon mixture with a proper molar weight was recommended as working fluid for space nuclear reactor power with CBC conversion. It is essential to figure out how the component of helium-xenon mixture affects the net system efficiency, in order to provide reference for the selection of appropriate cycle working fluid. After a discussion of the physical properties of different helium-xenon mixtures, the related physical properties are studied to analyze their affection on the key parameters of CBC, including adiabatic coefficient, recuperator effectiveness and normalized pressure loss coefficient. Then the comprehensive thermodynamics of CBC net system efficiency is studied in detail considering different helium-xenon mixtures. The physical properties study reveals that at 0.7 MPa and 400 K, the adiabatic coefficient of helium-xenon mixture increases with increased molar weight, from 0.400 (pure helium) to 0.414 (pure xenon), while recuperator effectiveness firstly increases and then decreases with the increase of molar weight, and the normalized pressure loss coefficient increases monotonically with molar weight increases. The thermodynamic analysis results show that the adiabatic coefficient has less effect on the net system efficiency, while the net system efficiency increases with increased recuperator effectiveness, and the net system efficiency decreases with normalized pressure loss coefficient increases. Finally, the mixture of helium-8.6% xenon was adopted as working fluid, instead of pure helium, for ensuring less turbine mechanicals (turbine and compressor) stages, and resulting maximum recuperator effectiveness. At the given cold / hot side temperature of 400 / 1300 K, the net system efficiency can reach 29.18% theoretically.

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