The rheological properties and microstructure of neutrally buoyant elliptical particle suspensions are studied using the immersed boundary-lattice Boltzmann method. For dilute suspensions containing only one particle, with the increase of aspect ratio Ar, the particle ceases to rotate due to the inertia at a critical aspect ratio ${\text{Ar}}_c$, and the value of ${\text{Ar}}_c$ decreases with increasing Re. The inertia-induced rotation arrest causes a nonmonotonic variation of particle alignment with the flow direction, and thence the relative viscosity, with increasing Ar, for a fixed Re. The relative viscosity first decreases, with increasing Ar due to the increasing alignment (on average) of tumbling particles; however, rotation arrest leads to a subsequent increase in the relative viscosity for $\text{Ar}>{\text{Ar}}_c$. This nonmonotonic variation persists over the entire range of Re and Ar examined here. For dense suspensions containing multiple particles, with increasing Ar, particles align more with the flow, but the orientation becomes almost constant when Ar is greater than a threshold ${\text{Ar}}_t$. Smaller values of ${\text{Ar}}_t$ are observed for higher Re. Meanwhile, ${\eta }_r$ decreases due to particle alignment for $\text{Ar}<{\text{Ar}}_t$ and then increases due to high particle-particle interaction for $\text{Ar}>{\text{Ar}}_t$. Further, the contributions of stresslet ($S$), particle acceleration stress ($P$), and Reynolds stress ($R$) on ${\eta }_r$ and the first normal stress difference $N_1$ are analyzed. In addition to the major contribution of stresslet, Reynolds stress contributes more as Ar increases at high Re. In addition, the microstructure and the probability density functions of lateral velocity $\left(U_y\right)$ and angular velocity (${\omega }_p$) are also analyzed. Our results may be helpful to understand the rheological properties of nonspherical particle suspensions.

Close

PrevNext

View figure in article

• 
• 
• 
• 
• 
• 
• 
• 
• 
• 
• 
• 
• 

• Fluid-particle interactions
• Interparticle interactions
• Particle-laden flows
• Rheological properties