Large-Eddy and Unsteady Reynolds-Averaged Navier-Stokes Simulations of an Axial Flow Pump for Cardiac Support

Abstract

The use of implantable pumps for cardiac support (Ventricular Assist Devices) has proven to be a promising option for the treatment of advanced heart failure. Avoiding blood damage and achieving high efficiencies represent two main challenges in the optimization process. To improve VADs, it is important to understand the turbulent flow field in depth in order to minimize losses and blood damage. The application of the Large-eddy simulation (LES) is an appropriate approach to simulate the flow field because turbulent structures and flow patterns, which are connected to losses and blood damage, are directly resolved. The focus of this paper is the comparison between an LES and an Unsteady Reynolds-Averaged Navier-Stokes simulation (URANS) because the latter one is the most frequently used approach for simulating the flow in VADs. Integral quantities like pressure head and efficiency are in a good agreement between both methods. Additionally, the mean velocity fields show similar tendencies. However, LES and URANS show different results for the turbulent kinetic energy. Deviations of several tens of percent can be also observed for a blood damage parameter, which depend on velocity gradients. Possible reasons for the deviations will be investigated in future works.

Influence of turbulent shear stresses on the numerical blood damage prediction in a ventricular assist device

“…From a physical point of view, equations (16) and (17) should lead to the same power loss P Loss . If this is fulfilled, it can be verified that the equivalent stresses are properly computed.…”

“…Nowadays, the flow simulations in VADs are commonly conducted using unsteady Reynolds-averaged Navier–Stokes (URANS) methods, in which a great part of the turbulent field is modeled. 17 Furthermore, the viscous shear stresses in the flow field are commonly analyzed using equivalent, scalar representations, 16 , 18–25 which are based on the second invariant I I S = 2 S i j S i j of the strain-rate tensor S i j . 3 These are, for example, the stress definition of Bludszuweit, 26 the van-Mises stresses 27 as well as the direct use of the second invariant 20 in the equivalent stress definition.…”

Shear Stress and Hemolysis Analysis of Blood Pump under Constant and Pulsation Speed Based on a Multiscale Coupling Model

“…e CFD simulation was based on FLUENT 17.0. e SST k-ω model was selected as the turbulence model, for the SST k-ω model contains the modified turbulent viscosity formulas and considers the effect of turbulent shear stress; it can simulate the near-wall flow field more accurately and proved to be suitable for blood pump simulation [15]. e expression of the k-ω SST model [28] is shown in (12) and (13), where k is the turbulent kinetic energy, ρ is the fluid density, μ is the dynamic viscosity, ω is the specific dissipation rate, μ t is turbulent eddy viscosity, and F 1 is the blending function, which is used to blend the k-ω model (F 1 � 0) and k-ε model (F 1 � 1), and the model coefficients are as follows: β � 0.075, β * � 0.09, σ k σ k � 2, σ ω � 2, and σ ω2 � 1/0.856. One has…”

“…During the process, there will be a shear flow field inside the blood pump, and the red blood cells may rupture under the effect of strong shear flow, thus inducing hemolysis [9,10]. To verify the rationality of blood pump structure and speed design, Computational Fluid Dynamics (CFD) is widely used in the flow field simulation of blood pump [11][12][13]. At present, there are many kinds of research focused on the flow field and hemolysis analysis of the blood pump at the constant rotation speed.…”

Study on the influence of dynamic/static interface processing methods on CFD simulation results of the axial-flow blood pump

“…[7][8][9][10] Since computational fluid dynamics (CFD) can simulate the complex flow state of fluid and realize the visualization of the flow field, CFD has been widely used in flow field analysis and structural optimization of blood pumps to solve these problems. [11][12][13][14] Blood is mixed with a large number of red blood cells and white blood cells. At present, there are some models 15 and methods [16][17][18] that can analyze the interaction between particles and fluid from a microperspective.…”