Effect of Emissary Vein on Hemodynamics of the Transverse- Sigmoid Sinus Junction

Objective: To investigate the effect of the blood flow direction and afflux location of emissary veins (EVs) on the hemodynamics of the transverse-sigmoid sinus (TS-SS) junction.Methods: A patient-specific geometric model was constructed using computed tomography venography (CTV) and 4D flow MR data from a venous pulsatile tinnitus (PT) patient. New EV models were assembled with the afflux at the superior, middle and inferior portions of the SS from the original model, and inlet and outlet directions were applied. Computational fluid dynamics (CFD) simulation was performed to analyze the wall pressure and flow pattern of the TS-SS junction in each condition.Results: Compared to the model without EVs, the wall pressure was greatly increased in models with inlet flow and greatly decreased in models with outlet flow. The more closely the EV approached the TS-SS, the larger the pressure in models with inlet flow, and the smaller the pressure in models with outlet flow. The flow streamline in the lateral part of the TS-SS junction was smooth in all models. The streamlines in the medial part were regular spirals in outlet models and chaotic in inlet models. The streamlines showed no obvious changes regardless of afflux location. The velocity at the TS-SS junction of inlet models were uniform, medium-low flow rate, while in control and outlet models were the lateral high flow rate and the central low flow rate.Conclusion: The flow direction and afflux location of EVs affect the hemodynamics of the TS-SS junction, which may influence the severity of PT.

Download Full-text

Stokes Flow Within Networks of Flow Branches

Journal of Fluids Engineering ◽

10.1115/1.4040832 ◽

2018 ◽

Vol 140 (12) ◽

Author(s):

Mustapha Hellou ◽

Franck Lominé

Keyword(s):

Flow Rate ◽

Stokes Flow ◽

Recurrence Formula ◽

Low Flow ◽

Navier Stokes Equation ◽

Flow Rates ◽

Analytical Results ◽

Hardy Cross ◽

Outlet Flow ◽

Low Flow Rate

Stokes flow in the branches of structured looped networks with successive identical square loops and T-junction branches is studied. Analytical expressions of the flow rate in the branches are determined for network of one, two, three, or four loops with junction head loss neglected relative to regular one. Then, a general expression of the flow rate is deduced for networks with more loops. This expression contains particularly a sequence of coefficients obeying to a recurrence formula. This sequence is a part of the fusion of Fibonacci and Tribonacci sequences. Furthermore, a general formula that expresses the quotient of flow rate in successive junction flow branches is given. The limit of this quotient for an infinite number of junction branches is found to be equal to 2+3. When the inlet and outlet flow rates are equal, this quotient obeys to a sequence of invariant numbers whatever the ratio of flow rate in the outlet branches is. Thus, the flow rate distribution for any configuration of inlet and outlet flow rates can be calculated. This study is also performed using Hardy–Cross method and a commercial solver of Navier-Stokes equation. The analytical results are approached very well with Hardy–Cross method. The numerical resolution agrees also with analytical results. However, the difference with the numerical results becomes significant for low flow rate in the junction branches. The flow streamlines are then determined for some inlet and outlet flow rate configurations. They particularly illustrate that recirculation flow takes place in branches of low flow rate.

Download Full-text

Backflow effects on mass flow gain factor in a centrifugal pump

Science Progress ◽

10.1177/0036850421998865 ◽

2021 ◽

Vol 104 (2) ◽

pp. 003685042199886

Author(s):

Wenzhe Kang ◽

Lingjiu Zhou ◽

Dianhai Liu ◽

Zhengwei Wang

Keyword(s):

Centrifugal Pump ◽

Mass Flow ◽

Flow Rate ◽

Low Frequency ◽

Gain Factor ◽

Low Flow ◽

Cavity Volume ◽

Cavitating Flows ◽

Inlet Tube ◽

Low Flow Rate

Previous researches has shown that inlet backflow may occur in a centrifugal pump when running at low-flow-rate conditions and have nonnegligible effects on cavitation behaviors (e.g. mass flow gain factor) and cavitation stability (e.g. cavitation surge). To analyze the influences of backflow in impeller inlet, comparative studies of cavitating flows are carried out for two typical centrifugal pumps. A series of computational fluid dynamics (CFD) simulations were carried out for the cavitating flows in two pumps, based on the RANS (Reynolds-Averaged Naiver-Stokes) solver with the turbulence model of k- ω shear stress transport and homogeneous multiphase model. The cavity volume in Pump A (with less reversed flow in impeller inlet) decreases with the decreasing of flow rate, while the cavity volume in Pump B (with obvious inlet backflow) reach the minimum values at δ = 0.1285 and then increase as the flow rate decreases. For Pump A, the mass flow gain factors are negative and the absolute values increase with the decrease of cavitation number for all calculation conditions. For Pump B, the mass flow gain factors are negative for most conditions but positive for some conditions with low flow rate coefficients and low cavitation numbers, reaching the minimum value at condition of σ = 0.151 for most cases. The development of backflow in impeller inlet is found to be the essential reason for the great differences. For Pump B, the strong shearing between backflow and main flow lead to the cavitation in inlet tube. The cavity volume in the impeller decreases while that in the inlet tube increases with the decreasing of flow rate, which make the total cavity volume reaches the minimum value at δ = 0.1285 and then the mass flow gain factor become positive. Through the transient calculations for cavitating flows in two pumps, low-frequency fluctuations of pressure and flow rate are found in Pump B at some off-designed conditions (e.g. δ = 0.107, σ = 0.195). The relations among inlet pressure, inlet flow rate, cavity volume, and backflow are analyzed in detail to understand the periodic evolution of low-frequency fluctuations. Backflow is found to be the main reason which cause the positive value of mass flow gain factor at low-flow-rate conditions. Through the transient simulations of cavitating flow, backflow is considered as an important aspect closely related to the hydraulic stability of cavitating pumping system.

Download Full-text

A Meanline Model for Impeller Flow Recirculation

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-51349 ◽

2008 ◽

Cited By ~ 10

Author(s):

Xuwen Qiu ◽

David Japikse ◽

Mark Anderson

Keyword(s):

Flow Rate ◽

Recirculation Zone ◽

Reverse Flow ◽

Low Flow ◽

Suction Surface ◽

Blade Loading ◽

Flow Recirculation ◽

Impeller Outlet ◽

Active Flow ◽

Low Flow Rate

Flow recirculation at the impeller inlet and outlet is an important feature that affects impeller performance, especially the power consumption at a very low flow rate. Although the mechanisms for this flow phenomenon have been studied, a practical model is needed for meanline modeling of impeller off-design performance. In this paper, a meanline recirculation model is proposed. At the inlet, the recirculation zone acts as area blockage to relieve the large incidence of the active flow at a low flow rate. The size of the blockage is estimated through a critical area ratio of an artificial “inlet diffuser” from the inlet to throat. The intensity of the reverse flow can then be calculated by assuming a linear velocity profile of meridional velocity in the recirculation zone. At the impeller outlet, a recirculation zone near the suction surface is established to balance the velocity difference on the pressure and suction sides of the blade. The size and the intensity of the outlet recirculation zone is assumed related to blade loading, which can be evaluated based on flow turning and Coriolis force. A few validation cases are presented showing a good comparison between test data and prediction by the model.

Download Full-text

Experimental Investigation of Surge Phenomena in a Transonic Centrifugal Compressor With Inlet Distortion

Volume 2E: Turbomachinery ◽

10.1115/gt2020-15426 ◽

2020 ◽

Author(s):

Sasuga Ito ◽

Masato Furukawa ◽

Satoshi Gunjishima ◽

Takafumi Ota ◽

Kazuhito Konishi ◽

...

Keyword(s):

Flow Rate ◽

Centrifugal Compressor ◽

Flow Instability ◽

Pressure Sensors ◽

Low Flow ◽

Inlet Distortion ◽

Transonic Centrifugal Compressor ◽

Response Pressure ◽

Surge Phenomena ◽

Low Flow Rate

Abstract Inlet distortion has influence on the aerodynamic performance of turbomachinery such as compressors, turbines and fans. On turbochargers, bent pipes are installed around the compressor due to the spatial limitations in the engine room of the vehicle. As the result, the compressor is operated with the distorted inflow. In the low flow rate operation, the distorted inflow also affects the flow instability like stall and surge. Especially, the operation range on the low flow rate side is defined based on the flow rate where surge occurs, so it is important to investigate the effect of the distorted inflow on surge. In this study, the effect of the inlet distortion to surge phenomena has been investigated by the experiments with a transonic centrifugal compressor. A bent pipe has been installed at the upstream of the compressor to generate a distorted flow. Experiments have been also conducted under the condition that a straight pipe was installed upstream of the compressor, and unsteady measurements with high response pressure sensors and an I-type hot wire probe have been carried out to each experiments. In addition, Fast Fourier transform (FFT) and Wavelet transform have been applied to the unsteady measurement results obtained from each experiment.

Download Full-text

A Comparative Assessment of Spalart-Shur Rotation/Curvature Correction in RANS Simulations in a Centrifugal Pump Impeller

Mathematical Problems in Engineering ◽

10.1155/2014/342905 ◽

2014 ◽

Vol 2014 ◽

pp. 1-9 ◽

Cited By ~ 5

Author(s):

Ran Tao ◽

Ruofu Xiao ◽

Wei Yang ◽

Fujun Wang

Keyword(s):

Kinetic Energy ◽

Centrifugal Pump ◽

Flow Rate ◽

Comparative Assessment ◽

Turbulence Kinetic Energy ◽

Low Flow ◽

Pump Impeller ◽

Curvature Correction ◽

Centrifugal Pump Impeller ◽

Low Flow Rate

RANS simulation is widely used in the flow prediction of centrifugal pumps. Influenced by impeller rotation and streamline curvature, the eddy viscosity models with turbulence isotropy assumption are not accurate enough. In this study, Spalart-Shur rotation/curvature correction was applied on the SSTk-ωturbulence model. The comparative assessment of the correction was proceeded in the simulations of a centrifugal pump impeller. CFD results were compared with existing PIV and LDV data under the design and low flow rate off-design conditions. Results show the improvements of the simulation especially in the situation that turbulence strongly produced due to undesirable flow structures. Under the design condition, more reasonable turbulence kinetic energy contour was captured after correction. Under the low flow rate off-design condition, the prediction of turbulence kinetic energy and velocity distributions became much more accurate when using the corrected model. So, the rotation/curvature correction was proved effective in this study. And, it is also proved acceptable and recommended to use in the engineering simulations of centrifugal pump impellers.

Download Full-text