Numerical study on flow separation in 90° pipe bend under high Reynolds number by k-ε modelling

Fully developed, statistically steady turbulent flow in straight and curved pipes at moderate Reynolds numbers is studied in detail using direct numerical simulations (DNS) based on a spectral elem ...

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Evolution of turbulence characteristics from straight to curved pipes

Particles impact characteristics on cutting surface during the abrasive water jet machining: Numerical study

In the present research, the effects of four 90-degree horizontal elbows with different curvature radii (17, 34, 51, and 68 cm) and an identical rectangular cross-section (20 * 34 mm) on a gas–liquid slug flow pattern have been studied experimentally and numerically. Gas and liquid superficial velocities in numerical and experimental parts were set in 2.5 m/s and 0.44 m/s, respectively. In the computational fluid dynamics section, the distribution of volume fraction, velocity, pressure, turbulence intensity, and swirling intensity parameters were investigated using the VoF model and the SST k-ω method. Experimental studies were conducted utilizing pressure data and signal processing tools to study the dominant frequency of slug flow alongside bandwidth distribution as well as the Shannon entropy. The results exhibited that although the dominant frequency of slug flow did not change after passing the 90-degree elbow, the frequency signal's bandwidth increased. In this regard, the application of Shannon entropy quantity revealed that the frequency distribution signal experienced a greater increase in bandwidth as the elbows’ curvature radius increases. The turbulent intensity of the elbows’ outlet reveals that by increasing the curvature radius, the flow field behaves smoother. Also, swirling intensity distribution shows that decreasing the elbow radius leads to increment in the swirling intensity.

Numerical and experimental simulation of gas-liquid two-phase flow in 90-degree elbow

Measurement of flow rate using straight pipes and pipe bends with integrated piezoelectric sensors

Curved pipes are very often used in hydraulic systems facilitating compact, lightweight designs. But they can also be the cause of complex secondary flows as the curvature brings change of velocity profile, generation of vortices and production of hydraulic losses. In the present study, turbulent single phase flows through circular 90 ̊ curved bend for different curvature ratio (Rc/D = 1 to 5), defined as the bend mean curvature radius (Rc) to pipe diameter (D) is investigated numerically for different Reynolds number (Re) ranging from 1×105 to 10×105. The purpose of this study is to simulate numerically the flow pattern and characterize the swirling secondary flow in 90 ̊ bends. Flow simulation using CFD techniques are performed to understand these phenomena. The k − ε model with SIMPLE method is used for present study. After validation of present model with published experimental data, a detail study has been performed to characterize the flow separation and the dependency of swirl intensity on Reynolds number and curvature ratio in 90 ̊ pipe bend for single phase turbulent flow.

Effect of Reynolds Number and Curvature Ratio on Single Phase Turbulent Flow in Pipe Bends

Pressure drop characteristics of turbulent flow through 90 degree pipe bends are numerically investigated by computational fluid dynamic simulation using k-e RNG turbulence model with standard wall function. After the validation of present model against existing experimental results, a detailed study has been performed to investigate the pressure distribution and pressure drop characteristics over a wide range of Reynolds number (Re = 1×10 5 to 10×10 5 ) and for different curvature ratio (RC/D = 1 to 5) to study pressure loss coefficient in terms of Reynolds number and curvature ration to provide cost effective solutions to design of the pipe bends. A number of important results have been achieved showing the distribution of pressure at different location throughout the bend for different Re and Rc/D. Numerical results shows the dependency of pressure distribution and pressure loss coefficient for different Reynolds number and curvature ratio throughout the bend.

Study on pressure drop characteristics of single phase turbulent flow in pipe bend for high reynolds number

A turbulent separation flow is one of the most complex flows in existence. Flow separation and reattachment phenomena take place on the lower curved wall under high-pressure gradient for high Reynolds number in different pipe bends. The present study deals with the numerical simulation of the turbulent separation reattachment flow under high Reynolds number in different curvature ratios. Through making use of k–e turbulence model, the turbulent single-phase flow via a 90-degree bend pipe is studied numerically. A more precise research has been conducted to discover the impact of Reynolds number (Re) as well as curvature ratio (Rc/D) on the reattachment and separation of flow inside the pipe bend. The separation region and the separation–reattachment points are reported here. Additionally, mean statistics of the primary and secondary velocity field flows in diverse sections and the occurrence of Dean vortices have been shown. It has been observed that bends with low curvature ratio enable flow separation to be clearly visualized. Distribution of velocity depicted that the secondary motion is clearly encouraged by the progress of fluid from the inner to the outer wall region of the bend resulting in the separation of flow. In general, this numerical study analyses the flow separation phenomenon and predicts the separation and reattachment locations in 90° bend pipe for different Reynolds numbers and bend curvatures.

Numerical Study on Turbulent Separation Reattachment Flow in Pipe Bends with Different Small Curvature Ratio

Present paper makes an effort to study the flow separation and velocity distribution for incompressible turbulent flow through 90o pipe bend due to the effect of guide vane installed in the bend portion. It has been observed here how the normalized velocity distribution profile changes if the guide vane is provided. k − ε turbulence model has been adopted for simulation purpose. After validating with existing experimental results, a detailed study has been performed for a particular Reynolds number and four different positions of guide vane. The value of Curvature ratio (Rc/D) has been considered as 1 for present study. The results obtained from the present study have been presented in terms of graphical form. A flow separation region was found at bend outlet for flow through 90o pipe bend without guide vane. This secondary flow separation region was absent for the cases which deals with the flow through 90o pipe bend with guide vane. Velocity distribution at seven different downstream positions have been presented in graphical form. Position to get a fully developed velocity distribution profile for each cases has been estimated on the basis of presented results.

Nityananda Nandi

Papers

Numerical study on flow separation in 90° pipe bend under high Reynolds number by k-ε modelling

Effect of Reynolds Number and Curvature Ratio on Single Phase Turbulent Flow in Pipe Bends

Study on pressure drop characteristics of single phase turbulent flow in pipe bend for high reynolds number

Numerical Study on Turbulent Separation Reattachment Flow in Pipe Bends with Different Small Curvature Ratio

Change in flow separation and velocity distribution due to effect of guide vane installed in a 90° pipe bend