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Martin Trulsson - One of the best experts on this subject based on the ideXlab platform.

  • unifying viscous and inertial regimes of discontinuous shear thickening suspensions
    Journal of Rheology, 2020
    Co-Authors: Junhao Dong, Martin Trulsson
    Abstract:

    The rheology of dense suspensions in the viscous regime can be characterized by the viscous number J and granular flows by the inertia number I, both relating the shear rate γ ˙ to the confining pressure P. Furthermore, several works have shown that the rheology of suspensions and granular flows can be unified, and this unification is used to characterize suspensions with non-negligible particle inertia from the viscous to the inertial regime (i.e., granular flows). There have also been recent works that apply this unification to suspensions where the number of frictional contacts increases upon the shear rate with Constant packing fraction, a model that has successfully described discontinuous shear thickening in suspension flows. We and other researchers have previously shown that the fraction of frictional contacts χ f is a key control parameter for friction-driven shear thickening in the viscous regime. It is, however, difficult to control and study the effect of the number of frictional contacts on the rheology of dense suspensions at Constant packing fraction as this quantity increases sharply around a threshold shear rate. In this work, we extend our previous work and use numerical simulations to study particle flows in both the viscous and inertial regimes as well as for suspensions in the crossover between these regimes with varying χ f. By having pressure-controlled simulations, we are able to keep χ f at values between 0 and 1, hence critically testing the validity of a unification at intermediate values. With the help of a binary model composed of nonfrictional and frictional particles, where χ f is well-controlled, we manage to obtain expressions for constitutive laws in both limits. For the critical load model, we find a simple relationship between χ f and the pressure-rescaled threshold force f ^ applicable for both the viscous and inertial regimes. Combining these expressions, we then show that suspensions in the crossover between these regimes can be characterized by four dimensionless numbers, f ^, K, K μ, and K z, where the last three are simple combinations of J and I and verified against numerical simulations. These expressions can be further simplified by approximating K μ = K, which we show is a good approximation close to shear jamming or at low Stokes numbers. In the end, we construct a dimensionless parameter encoding various shear protocols and show predictions of behaviors of suspensions under different shear conditions. Having derived constitutive relations from Constant pressure simulations, we finally test our relations under Constant Volume Assumption which indeed well captures the various discontinuous shear thickening behaviors seen at different Stokes numbers. Finally, we discuss the role of having a varying microscopic friction coefficient μ p as a function of the normal force.The rheology of dense suspensions in the viscous regime can be characterized by the viscous number J and granular flows by the inertia number I, both relating the shear rate γ ˙ to the confining pressure P. Furthermore, several works have shown that the rheology of suspensions and granular flows can be unified, and this unification is used to characterize suspensions with non-negligible particle inertia from the viscous to the inertial regime (i.e., granular flows). There have also been recent works that apply this unification to suspensions where the number of frictional contacts increases upon the shear rate with Constant packing fraction, a model that has successfully described discontinuous shear thickening in suspension flows. We and other researchers have previously shown that the fraction of frictional contacts χ f is a key control parameter for friction-driven shear thickening in the viscous regime. It is, however, difficult to control and study the effect of the number of frictional ...

Junhao Dong - One of the best experts on this subject based on the ideXlab platform.

  • unifying viscous and inertial regimes of discontinuous shear thickening suspensions
    Journal of Rheology, 2020
    Co-Authors: Junhao Dong, Martin Trulsson
    Abstract:

    The rheology of dense suspensions in the viscous regime can be characterized by the viscous number J and granular flows by the inertia number I, both relating the shear rate γ ˙ to the confining pressure P. Furthermore, several works have shown that the rheology of suspensions and granular flows can be unified, and this unification is used to characterize suspensions with non-negligible particle inertia from the viscous to the inertial regime (i.e., granular flows). There have also been recent works that apply this unification to suspensions where the number of frictional contacts increases upon the shear rate with Constant packing fraction, a model that has successfully described discontinuous shear thickening in suspension flows. We and other researchers have previously shown that the fraction of frictional contacts χ f is a key control parameter for friction-driven shear thickening in the viscous regime. It is, however, difficult to control and study the effect of the number of frictional contacts on the rheology of dense suspensions at Constant packing fraction as this quantity increases sharply around a threshold shear rate. In this work, we extend our previous work and use numerical simulations to study particle flows in both the viscous and inertial regimes as well as for suspensions in the crossover between these regimes with varying χ f. By having pressure-controlled simulations, we are able to keep χ f at values between 0 and 1, hence critically testing the validity of a unification at intermediate values. With the help of a binary model composed of nonfrictional and frictional particles, where χ f is well-controlled, we manage to obtain expressions for constitutive laws in both limits. For the critical load model, we find a simple relationship between χ f and the pressure-rescaled threshold force f ^ applicable for both the viscous and inertial regimes. Combining these expressions, we then show that suspensions in the crossover between these regimes can be characterized by four dimensionless numbers, f ^, K, K μ, and K z, where the last three are simple combinations of J and I and verified against numerical simulations. These expressions can be further simplified by approximating K μ = K, which we show is a good approximation close to shear jamming or at low Stokes numbers. In the end, we construct a dimensionless parameter encoding various shear protocols and show predictions of behaviors of suspensions under different shear conditions. Having derived constitutive relations from Constant pressure simulations, we finally test our relations under Constant Volume Assumption which indeed well captures the various discontinuous shear thickening behaviors seen at different Stokes numbers. Finally, we discuss the role of having a varying microscopic friction coefficient μ p as a function of the normal force.The rheology of dense suspensions in the viscous regime can be characterized by the viscous number J and granular flows by the inertia number I, both relating the shear rate γ ˙ to the confining pressure P. Furthermore, several works have shown that the rheology of suspensions and granular flows can be unified, and this unification is used to characterize suspensions with non-negligible particle inertia from the viscous to the inertial regime (i.e., granular flows). There have also been recent works that apply this unification to suspensions where the number of frictional contacts increases upon the shear rate with Constant packing fraction, a model that has successfully described discontinuous shear thickening in suspension flows. We and other researchers have previously shown that the fraction of frictional contacts χ f is a key control parameter for friction-driven shear thickening in the viscous regime. It is, however, difficult to control and study the effect of the number of frictional ...

Trulsson Martin - One of the best experts on this subject based on the ideXlab platform.

  • Unifying viscous and inertial regimes of discontinuous shear thickening suspensions
    'Society of Rheology', 2020
    Co-Authors: Dong Junhao, Trulsson Martin
    Abstract:

    The rheology of dense suspensions in the viscous regime can be characterized by the viscous number J and granular flows by the inertia number I, both relating the shear rate γ - to the confining pressure P. Furthermore, several works have shown that the rheology of suspensions and granular flows can be unified, and this unification is used to characterize suspensions with non-negligible particle inertia from the viscous to the inertial regime (i.e., granular flows). There have also been recent works that apply this unification to suspensions where the number of frictional contacts increases upon the shear rate with Constant packing fraction, a model that has successfully described discontinuous shear thickening in suspension flows. We and other researchers have previously shown that the fraction of frictional contacts χ f is a key control parameter for friction-driven shear thickening in the viscous regime. It is, however, difficult to control and study the effect of the number of frictional contacts on the rheology of dense suspensions at Constant packing fraction as this quantity increases sharply around a threshold shear rate. In this work, we extend our previous work and use numerical simulations to study particle flows in both the viscous and inertial regimes as well as for suspensions in the crossover between these regimes with varying χ f. By having pressure-controlled simulations, we are able to keep χ f at values between 0 and 1, hence critically testing the validity of a unification at intermediate values. With the help of a binary model composed of nonfrictional and frictional particles, where χ f is well-controlled, we manage to obtain expressions for constitutive laws in both limits. For the critical load model, we find a simple relationship between χ f and the pressure-rescaled threshold force f applicable for both the viscous and inertial regimes. Combining these expressions, we then show that suspensions in the crossover between these regimes can be characterized by four dimensionless numbers, f, K, K μ, and K z, where the last three are simple combinations of J and I and verified against numerical simulations. These expressions can be further simplified by approximating K μ = K, which we show is a good approximation close to shear jamming or at low Stokes numbers. In the end, we construct a dimensionless parameter encoding various shear protocols and show predictions of behaviors of suspensions under different shear conditions. Having derived constitutive relations from Constant pressure simulations, we finally test our relations under Constant Volume Assumption which indeed well captures the various discontinuous shear thickening behaviors seen at different Stokes numbers. Finally, we discuss the role of having a varying microscopic friction coefficient μ p as a function of the normal force

Luc Bauwens - One of the best experts on this subject based on the ideXlab platform.

  • On the Validity of the Constant Volume Assumption in Shock Tube Experiments
    28th International Symposium on Shock Waves, 2012
    Co-Authors: J. Melguizo-gavilanes, Luc Bauwens
    Abstract:

    Induction time is an important measurement obtained in shock tube experiments, for use in calibration or validation of chemical kinetic schemes. Typically, these times are taken as representative of spatially uniform, Constant Volume combustion induction times. The actual process that happens in the shock tube is clearly more complex, however. In a first approximation, the flow might be described as being one-dimensional, inviscid and reactive, behind an incident or reflected shock, although in reality, multi-dimensional and viscous effects will play a role [1, 2]. The Constant Volume Assumption may yield good results when dealing with highly diluted mixtures at relatively high post-shock temperatures [3]. However in other circumstances, such as more reactive mixtures at low post-shock temperatures, strong spatial pressure gradients may be present, potentially leading to significant uncertainties or inaccuracies. Assessing the actual accuracy of the Constant Volume Assumption or alternatively improving the means used in validating kinetic schemes will require at the very least a one-dimensional simulation of the reacting flow in shocked mixture. Although the required simulations are one-dimensional, they are not straightforward, because the initial conditions are singular in the sense that at the instant when chemistry is triggered by the passage of the shock into the reactive mixture, there is no simulation domain containing reactive mixture, and that domain subsequently grows as the shock propagates. We have developed techniques that handle these difficulties, mainly in the context of the deflagration-to-detonation scenario [4]. The full unsteady problem is described by the reactive Euler’s equations, which are transformed from its original formulation, in which space x and time t are used as independent variables to η = x/t and t. This transformation effectively overcomes the non-existence of the initial physical domain. Chemistry is modeled using a three-step chain-branching mechanism originally proposed by Short & Quirk [5].

Dong Junhao - One of the best experts on this subject based on the ideXlab platform.

  • Unifying viscous and inertial regimes of discontinuous shear thickening suspensions
    'Society of Rheology', 2020
    Co-Authors: Dong Junhao, Trulsson Martin
    Abstract:

    The rheology of dense suspensions in the viscous regime can be characterized by the viscous number J and granular flows by the inertia number I, both relating the shear rate γ - to the confining pressure P. Furthermore, several works have shown that the rheology of suspensions and granular flows can be unified, and this unification is used to characterize suspensions with non-negligible particle inertia from the viscous to the inertial regime (i.e., granular flows). There have also been recent works that apply this unification to suspensions where the number of frictional contacts increases upon the shear rate with Constant packing fraction, a model that has successfully described discontinuous shear thickening in suspension flows. We and other researchers have previously shown that the fraction of frictional contacts χ f is a key control parameter for friction-driven shear thickening in the viscous regime. It is, however, difficult to control and study the effect of the number of frictional contacts on the rheology of dense suspensions at Constant packing fraction as this quantity increases sharply around a threshold shear rate. In this work, we extend our previous work and use numerical simulations to study particle flows in both the viscous and inertial regimes as well as for suspensions in the crossover between these regimes with varying χ f. By having pressure-controlled simulations, we are able to keep χ f at values between 0 and 1, hence critically testing the validity of a unification at intermediate values. With the help of a binary model composed of nonfrictional and frictional particles, where χ f is well-controlled, we manage to obtain expressions for constitutive laws in both limits. For the critical load model, we find a simple relationship between χ f and the pressure-rescaled threshold force f applicable for both the viscous and inertial regimes. Combining these expressions, we then show that suspensions in the crossover between these regimes can be characterized by four dimensionless numbers, f, K, K μ, and K z, where the last three are simple combinations of J and I and verified against numerical simulations. These expressions can be further simplified by approximating K μ = K, which we show is a good approximation close to shear jamming or at low Stokes numbers. In the end, we construct a dimensionless parameter encoding various shear protocols and show predictions of behaviors of suspensions under different shear conditions. Having derived constitutive relations from Constant pressure simulations, we finally test our relations under Constant Volume Assumption which indeed well captures the various discontinuous shear thickening behaviors seen at different Stokes numbers. Finally, we discuss the role of having a varying microscopic friction coefficient μ p as a function of the normal force