1. Introduction
A brush seal represents a form of contact seal technology. According to
Figure 1, a common brush seal comprises slender bristles densely arranged between the front and pack plates.
Based on the research of Bayley and Long (reference provided), it was determined that the distance between the bristles ranges between ((bristle diameter)/7) and ((bristle diameter)/10) or (0.007 and 0.010) mm. Consequently, a bristle gap of (bristle diameter)/8 mm was selected as equal to 0.009525 mm. A brush seal is typically made of two plates, a front plate and a back plate, that partially enclose the bristles. The bristle pack material, the density at which they are packed, the amount of clearance or interference between the rotor surface and the bristle pack, the heights of the front and back plates, the angle at which the bristles are inclined, and the methods used to balance the pressure on the two sides of the seal can all vary depending on the specific design [
1,
2,
3]. Throughout the operational condition, the brush seal contacts the corresponding rotor. The only gaps that permit leakage flow through the seal are those located within the bristle region corresponding to the fence height. When compared to other types of seals, brush seals can significantly reduce the rate of leakage and require less axial space [
4]. Brush seals are now more frequently used in steam turbines and industrial gas turbines, either alone or in combination with labyrinth seals, to greatly increase the power output and efficiency capacities despite their original design being for aero-engines [
5,
6].
Comparing the brush seal to the labyrinth seal, leakage can be reduced by 70 percent [
7]. In addition to dramatically decreasing leakage loss at the dynamic and static gaps, the brush seal can also do so for the entire system [
8]. Although brush seals cost more to produce than labyrinth seals, they have a much greater potential for long-term cost savings [
9]. Due to the substantial sealing clearance inherent between the labyrinth teeth and the shaft, clearance brush seals exhibit sealing performance similar to that of labyrinth seals [
5]. Due to friction, brush seals can produce a lot of heat, especially at high rotor speeds and high pressure. The bristles are normally inclined in the direction of rotation and angled between 30 and 60 degrees from the shaft; this helps to decrease the friction and heat generation [
10]. Investigating how brush seals control leakage and heat transfer is important to ensuring sealing performance and durability over time. In this study, a thorough numerical simulation of the leakage characteristics of brush seals will be conducted using computational fluid dynamics (CFD). The study will thoroughly study the flow patterns within the brush seal using a two-dimensional axisymmetric, anisotropic porous media model to investigate the performance of the brush seal.
There are two basic groups of the brush seal numerical simulation: those that simulate the bristle pack as a physical entity and those that consider it as a porous medium. The entity model consists of two unique models: the 2D and 3D tube bank models, both of which are practical choices, and the 3D tube bank model, which is used to study the anisotropic flow in the bristle pack but requires a lot of computing resources, time, and power [
11]. In the field of brush seals, the porous media model is a hot topic. However, calibrating resistance coefficients within the brush seal bristle pack is time consuming and expensive [
12].
Chew et al. [
13,
14] investigated the non-uniform porosity within the bristle pack and developed a computational approach for determining the resistance coefficient of the bristle pack based on pressure distributions in various orientations. Prostler [
15] created a three-dimensional computational method for the porous medium model. Dogu [
16] calculated the viscous resistance coefficient of the axial direction using Darcy’s law and Bernoulli’s equation and then calibrated the resistance coefficient of the radial direction using experimental data. Wiid [
17] used the water flowing through the bristle pack to compute the resistance coefficient.
Thomas et al. [
18] studied how the permeability of brush seals changes when they are modeled as a porous medium. They found that the viscous effect, such as friction between the bristles and the fluid, is the most important factor in determining the leakage through the brush seal.
Bayley and Long [
19] conducted an experimental investigation aimed at calibrating the coefficients of a porous media model for brush seals. This involved measuring leakage flow and pressure distribution for brush seals with an interference structure of 0.25 mm and subsequently utilizing the experimental data to calibrate the model coefficients.
Many scholars, including [
20,
21,
22], have explored the leakage performance of brush seals analytically, experimentally, and numerically. The results demonstrated that the numerical and experimental results are in excellent agreement.
The tube bank model is commonly applied in thermal fluid machinery contexts, such as heat exchangers in boilers and air conditioners, and is employed in numerical simulations to analyze the performance of brush seals. Researchers typically utilize the tube bank model for examining brush seal performance.
Several experiments and numerical simulations have been investigated over the last ten years to investigate how well brush seals reduce leakage. These investigations helped our comprehension of the leakage flow attributes of brush seals, which is crucial for their efficient design and utilization [
23,
24,
25].
This paper presents a new method for modeling the brush seal that is more accurate and efficient than previous methods. The method uses a 2D axisymmetric model to determine the resistance coefficients of brush seals, which are then used to create a porous medium model of the brush seals. The effects of the pressure ratio on the leakage flow of contact and clearance brush seals will be discussed. This method combines the advantages of the 2D axisymmetric model and the porous media model, allowing for the simulation of flow anisotropy and the visualization of brush seals. Additionally, this method provides a convenient alternative to designing and analyzing brush seals, which can save time and money on the calibration of the porous media model.