1. Introduction
The World Health Organization (WHO) reports that 68 percent of deaths are caused by non-communicable diseases, of which cardiovascular disorders account for one-third. According to evidence from various physiological studies, disorders of the blood arteries and the heart, such as heart attacks and strokes, are the major cause of mortality globally. Atherosclerosis, a condition that results in plaque building up in the artery lumen and manifesting as stenosis, causes these events because it prevents blood from reaching distant body cells. An aneurysm may be caused by multiple factors that result in the breaking down of the well-organized structural components (proteins) of the aortic wall that provide support and stabilize the wall. The exact cause has yet to be fully discovered. Atherosclerosis is thought to play an essential role in aneurysmal disease. Numerous researchers ([
1,
2,
3,
4,
5,
6,
7]) have theoretically and experimentally explored the mechanics of blood circulation via stenosed arteries. The physical characteristics of EMHD of the bloodstream through an artery in the presence of electroosmotic forces with both aneurysm and stenosis are theoretically investigated by Abdesalam et al. [
8]. Zhang et al. [
9] studied the impacts of nanoparticle volume fraction on plaque disintegration during transit by employing a two-phase mixing approach. By assuming that blood viscosity is hematocrit-dependent, Poonam et al. [
10] analyzed the impact of hybrid nanoparticles on hemodynamical blood flow parameters via a curved artery with aneurysm and stenosis. Basha et al. [
11] examined the fluid transport behavior of Au-Cu/Blood hybrid nanofluid via an artery having the inclination and irregular stenosis. Using computational fluid dynamics (CFD) in COMSOL Multiphysics, Waqas et al. [
12] investigated the numerical modeling of hybrid nanofluid with nanoparticles such as gold and silver over a stenotic artery.
A novel class of functional fluids known as ”nanofluids” has been produced by the colloidal combination of these nanoparticles in the conventional base fluid, having less effective thermophysical properties. As a result, the nanofluid generated has increased thermal conductivity, thermal diffusivity, viscosity, and convective heat transfer coefficient, among other thermophysical properties. These nanoparticles, or nanofluids, have been used strategically in numerous heat transfer applications with outstanding success. However, more biomedical engineering applications, such as drug transport, tissue regeneration, wound healing, and biomagnetic nano-pharmacodynamics, are beginning to emerge. Badfar et al. [
13] used Fe
O
nanoparticles coated with a drug to carry out the magnetic drug targeting in the vessel’s stenosis region. They also investigated how the wire’s location as a magnetic source affected the MDT. In their numerical simulation of magnetic nanoparticle-based medication delivery, Varmazyar et al. [
14] used two cases: one with a slight obstruction and the other with two mild and severe blockages. Ramadan et al. [
15] analyzed the blood flow incorporating gold nanoparticles via a stenosed tapering artery using the Phan-Thien-Tanner fluid model to treat the terrible cancer disease. In order to accurately characterize the blood flow, including TiO
and Ag nanoparticles, Saeed et al. [
16] used a couple-stress fluid model. Sharma et al. [
17] carried out entropy analysis for blood flow with temperature-dependent viscosity through a tapered artery having multiple-stenosis incorporating hybrid nanoparticles. Mekheimer et al. [
18] used biomedical models of drug distribution via nanoparticles to address the issue of synovitis in sick tissues. Khanduri et al. [
19] investigated the influence of Hall and ion slips on MHD blood flow through a catheterized artery with multiple stenosis and thrombosis while suspending Au and GO nanoparticles in the blood. Sharma et al. [
20] analyzed the effects of heat transfer and body acceleration on unsteady MHD blood flow through a curved artery in the presence of stenosis and aneurysm using hybrid nanoparticles. Dolui et al. [
21] investigated the combined influence of non-linear thermal radiation and externally induced magnetic field to graphically evaluate the flow characteristics of tri-hybrid (Cu–Ag–Au), hybrid (Cu–Au), and single (Au) nanofluids flowing through arteries with composite stenosis. Karmakar et al. [
22] formulated a mathematical framework for the hemodynamical characterization of blood circulation containing trihybrid nanoparticles inside an eccentric endoscopic artery canal with a flexible wall in the presence of buoyancy and electro-osmotic pressures.
The majority of the research described above treated blood as a Newtonian fluid and investigated the relationship between arterial stenosis and blood flow dynamics. The blood behaves in the larger-diameter arteries with an assertive Newtonian behavior when shear rates are greater than 100 s
. However, because blood is a suspension of cells, it is widely known that arteries with smaller diameters and lower shear rates exhibit remarkable non-Newtonian blood behavior. The Casson fluid flow model has recently become more well-known attributable to its intriguing applications in everyday life. The Casson fluid flow model is widely used in modern science. Casson fluid exhibits yield stress characteristics. The Casson fluid changes into the Newtonian fluid when the yield stress is high enough. Walawender et al. [
23] showed that blood can be modeled using Casson fluid by measuring pressure drop and volumetric flow rate experimentally. Sarifuddin et al. [
24] used the Marker and Cell approach to numerically solve the equations as they investigated the effect of two-dimensional blood flow while supposing blood to be Casson fluid flowing through an unsteady stenosed artery. Using the Casson model to describe the liquid’s non-Newtonian viscosity, Debnath et al. [
25] investigated the effects of a 1st-order homogeneous-heterogeneous chemical reaction in an annular pipe. Darcy’s law was applied by Ali et al. [
26] to examine the Casson fluid flow behavior in a 2-D porous channel using a vorticity-stream function method. Das et al. [
27] explored solute dispersion via a stenotic tube with an absorptive wall in their study with Casson fluid characterizing the rheology of blood. Padma et al. [
28] aimed to investigate how yield stress affected the EMHD motion of Casson fluid and nanoparticles as they flow via a mildly blocked inclined tapering artery.
In their study of blood flow through stenosed arteries, most researchers assumed the artery walls to be impermeable. The primary function of an endothelial wall in the human body is to prevent the exchange of substances between moving tissues and blood. In actuality, the endothelium wall is permeable due to the presence of ultramicroporous structures. Increased permeability is caused by the accumulation of cholesterol, fatty acids, dilated artery walls, and arterial wall injury. Beaver and Joseph’s [
29] experimental work revealed that Darcy’s law would not always satisfy the governing equations near the wall. So, they also formulated a boundary condition at the permeable wall. Mishra et al. [
30] analyzed the influence of the wall’s permeability via an artery having composite stenosis. Ijaz and Nadeem [
31] discussed how the blood flows through a permeable walled stenosed artery is affected by copper nanoparticles. Akbar et al. [
32] formulated a mathematical model to simulate blood flow through a composite stenosed artery with permeable walls. Shahzadi and Bilal [
33] investigated the flow of blood in a stenosed bifurcated artery containing Copper and its oxide as a drug to reduce the stress and lesions of an atherosclerotic artery. They considered the artery to be permeable as well as compliant. A mathematical model for medication delivery employing gold and alumina nanoparticles via a porous artery with stenosis was developed by Gandhi et al. [
34]. In their computational analysis through a curved stenosed permeable artery, Sharma et al. [
35] took into account the blood flow in two phases - the core and the plasma region, respectively. Further, Kumawat et al. [
36] examined the entropy generation with a chemical reaction through a permeable curved artery. Sharma and Gandhi [
37] investigated unsteady heat and mass transmission through a stretching surface immersed in a Darcy-Forchheimer porous medium.
None previously mentioned research assessed the KKL model for the effective thermal conductivity and viscosity models. The primary focus of engineers, physicians, and biologists is on improving the working fluid’s thermal performance. The nanosized particle dispersion in the base fluid is one of the current methods. Now, it is a well-known truth that nanoparticles of one sort or more are trustworthy agents for improving the thermal performance of the working fluid. There are several documented relationships between the thermal characteristics of the base fluid, nanofluid, and solid nanoparticles. One set of relationships has more restrictions than another, though. The role of nanoparticles in drug delivery mechanisms is the most effective technique to cure several problems such as atherosclerosis, aneurysms, angina, or heart attacks. Also, the main concern of physicians during any surgery is to regulate the human body temperature in the presence of external factors such as radiation, heat source, etc. The literature survey reveals that the KKL correlations ([
38,
39,
40]) take temperature, volume fraction, and nanoparticle size into account when calculating how Brownian motion would affect a fluid’s thermal performance. To replicate the nanofluid flow between two parallel plates—one of which is heated from the outside and the other into which coolant fluid is injected, Kandelousi [
41] used KKL correlations. Mehmood et al. [
42] used the KKL model to assess the effective thermal conductivity and dynamic viscosity of the alumina-water nanofluid in a porous cavity under the influence of an inclined magnetic field. By combining the Cattaneo-Christov flux model with KKL correlations and considering the dispersion of CuO and Al
O
nanoparticles in blood, Rana and Nawaz [
43] examined the improvement of heat transmission. Utilizing the KKL model, Malik et al. [
44] thoroughly examined fluid flow between two vertical rotating plates with permeable surfaces, including nanoparticles. Shahzad et al. [
45] investigated the behavior of Sutterby nanofluid passing through a sloping sheet considering copper oxide-engine oil (CuO-EO). They determined the effective viscosity and thermal conductivity using the KKL model. Ramzan et al. [
46] investigated the heat transmission of MHD water-based nano liquid flow across a permeable stretched curved surface affected by an induced magnetic field by employing KKL correlations for dynamic viscosity and thermal conductivity.
The literature survey shows that no work has been published yet that addresses optimizing heat transfer utilizing the Casson fluid model and KKL correlations along with temperature-dependent viscosity through the irregular stenotic artery with an aneurysm. Therefore, the present study aims to study the blood flow through a stenotic artery with an aneurysm affected by the magnetic field, electric field, Joule heating, radiation, and viscous dissipation. The present work is divided into five main sections: The first part is the introduction concerning KKL correlations and other parameters considered in this work. Secondly, we have the mathematical modeling part, which initially describes KKL correlations for the simulation of nanofluid. Afterward, the model’s geometrical representation and governing equations are presented, followed by non-dimensionalization and radial coordinate transformation. The third section deals with the numerical solution, which firstly discusses the discretization of governing equations and then the validation of the employed Crank-Nicolson finite difference scheme. The validation of the present work is divided into two parts: (i) mesh independence and (ii) validation with existing literature. The following section is the results and graphical analysis, which discusses the influence of various influential parameters involved in the flow. The novelty of the present work is expressed as:
KKL correlations are employed for modeling nanofluid flow through a permeable stenosed artery.
EMHD Casson fluid flow is considered along with Joule heating, radiation, and viscous dissipation.
The relative % variation for the Nusselt number has been calculated and portrayed using bar graphs.
3. Numerical Procedure
The partial differential Equations (
41) and (
42) are coupled differential equations, therefore obtaining an analytic solution is too difficult. On the other hand, numerical approaches can yield a highly accurate solution. An unconditionally stable implicit finite difference (Crank–Nicolson) approach is used in this case. The superscripts and subscripts are not taken into account throughout the discretization process for Equations (
41) and (
42).
3.1. Discretization
On employing the values of thermophysical features of nanofluid and discretizing the governing Equations (
41) and (
42) using Crank-Nicolson scheme, the desired form of equations is:
The Crank-Nicolson scheme employed in the current analysis is, however, stable for all values for
and
still, a minimal value is considered with great precision as
and
. It is noticed that no further change occurs in the values of hemodynamical parameters studied in the research with decreasing values of
and
. A total of
grid points have been considered in the spatial direction, with
being the step size, whereas
grid points are considered temporal. The value at any time instant
is given as
,
being a small increment in time. As the scheme employed is an implicit one; therefore a system of equations is obtained, and it is in the form of a tri-diagonal system which can be solved with the Tri-diagonal Matrix Algorithm (TDMA) [
53].
Equation (
46) corresponds to a tri-diagonal system, which is given by
where
,
,
,
,
,
,
.
The tri-diagonal system corresponding to Equation (
47) is given by
where
,
,
,
,
,
.
.
3.2. Validation of the Employed Numerical Scheme
The Crank-Nicolson finite difference method has been applied in the present work. To check the accuracy of the applied numerical scheme, two methods have been adopted. Firstly, a mesh independence test is performed, which includes both grid independence as well as time independence. Also, validation has been performed with the existing model of Zaman et al. [
54].
3.2.1. Mesh Independence
A “grid-independency test” is used to optimize the suggested grid system for the current study, allowing for the selection of a mesh density that is both computationally accurate and economically acceptable.
Table 3 lists the ideal grid size (100 × 100) that achieves enough precision; any other mesh size refinement does not provide an increase in accuracy. In accordance with
Table 4, the “time-independency test” provides the best time-step size of dt = 0.01.
3.2.2. Validation with Existing Literature
The accuracy of our results has been verified by validating it with the existing model of Zaman et al. [
54]. The effect of EMHD, Joule heating, viscous dissipation, and radiation has been neglected to verify the results with the simplest existing model of Zaman et al. [
54]. As the Casson fluid parameter in the current work approaches infinity (
), the current model approaches the Newtonian model in [
54]. The KKL scheme adopted for variable viscosity and thermal conductivity is also replaced by a generalized model for nanofluids. The results have been compared for Al
O
nanoparticles, which are common in both research work. For verification,
Figure 2a,b have been plotted. A comparison with the existing literature [
54] reveals a good agreement to support the validity of the present solutions.