Reynolds-averaged Navier-Stokes Computational Fluid Dynamics Research Articles

Aerodynamic Feasibility Investigation of the Novel Experimental Rig on Turbine Blade Tip With High Relative Motion

Abstract The relative casing motion can significantly alter the over-tip-leakage (OTL) flow aerodynamic performances. Traditional tip experimental facilities for relative motion researches, including stationary linear cascade with low-speed moving belt, annular cascade with rotating outer wall, and full-scale experimental rig with rotating blade, were either extremely costly or not capable to reproduce engine-representative casing Mach number. Very recently, a novel design concept for high-speed disk rotor rig has been proposed for tip research. Subsequent to this research, the present study evaluates the aerodynamic performances and the periodicity of the disk rotor rig design using Reynolds-averaged Navier–Stokes computational fluid dynamics simulation. Furthermore, first-of-its-kind experimental results of total pressure loss distributions measured by five-hole probe under high relative casing Mach number are reported. The results demonstrate the applicability of the disk rotor experimental rig for tip aerodynamic investigations.

Unsteady Upwind Aerodynamics of a Sailing Yacht

_ Sail aerodynamics has been a researched topic since the start of competitive racing, such as the America's Cup and Whitbread Round the World Race. Recently, with restrictions on the use of wind tunnels and towing tanks in the America's Cup, there has been an increase in computational fluid dynamics (CFD) to study the aerodynamics and performance of yacht sails. These studies typically model steady-state conditions, but in contrast, this paper demonstrates the implementation of dynamic wind conditions in Reynolds Averaged Navier Stokes CFD and the effects it has on the aerodynamics of a yacht sailing upwind. A user-defined function was used to give a velocity profile and vary the wind direction with time to simulate a gust condition with a period of 10 s. In addition to the gusting model, steady models were run for the apparent wind angles (AWA) experienced in the gust to see if the dynamic wind conditions could be modelled by a series of steady state snapshots. The results show minor differences in the streamlines of two models and the pressure distributions show no significant difference. There is only a slight difference in sail forces at high AWAs. Although further research would be required this information could be valuable to anyone using CFD to test sail designs. Keywords CFD; transient; steady; upwind; UDF; RANS

Experimental study on aerodynamic performance of turbine blade squealer tip with different trailing edge designs under high-speed relative casing motion

Over-tip leakage (OTL) flow leads to great aerodynamic performance reduction in high-pressure turbine, reasonable blade tip design can effectively control the loss caused by OTL flow. The relative casing motion is one of the key boundary conditions that can significantly influence OTL flow. In this study, aerodynamical tests were conducted for a high-pressure squealer tip with different trailing edge designs of full cavity squealer tip, pressure-side cutback and suction-side cutback at both stationary and rotating conditions. Loss distribution and blade near tip loading of different trailing edge structures at high-speed rotating condition are firstly reported and evaluated. The result indicates that pressure-side cutback design significantly increases the aerodynamic loss compared with full cavity tip, while suction-side cutback design has close overall loss to full cavity tip. This conclusion was consistent with numerical simulation based on Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) analysis, which reveals that pressure-side cutback design causes the cavity vortex leaks earlier compared with full cavity tip, a small vortex formed at cut region forms and results in higher total pressure loss. The effect of relative motion between blade tip and shroud reinforces this trend. The total pressure loss difference can reach 42 % compared with 8 % in stationary condition, which indicates that relative casing motion needs to be take into consideration when ranking different tip sealing designs.

RANS-Based Aerodynamic Shape Optimization of a Wing with a Propeller in Front of the Wingtip

Accounting for propeller–wing interaction allows for the design of more efficient propeller aircraft through strategic propulsion integration. In this paper, the cruise drag of a wing with a propeller located in front of the wingtip is minimized using twist and airfoil-shape design variables. Reynolds-averaged Navier–Stokes computational fluid dynamics with an actuator-disk approach is used for the flow simulations, and a gradient-based algorithm is used for the optimization. Changing the rotation direction of the propeller and optimizing the twist and airfoil shapes of the wing are found to impact the aerodynamic performance significantly, as expected. However, optimizing the wing while accounting for the propeller slipstream during optimization provides little benefit over optimizing it without accounting for the propeller slipstream—a difference of less than one drag count.

Numerical and experimental analysis of the formation of nitrogen oxides in a non-premixed industrial gas burner

Nitrogen oxides (NOx) formation in a non-premixed industrial gas burner is analyzed with Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics, using the Flamelet Generated Manifold (FGM) approach for chemistry and the Reynolds stress model for turbulence closure. Analysis and validation of the numerical methodology use both the RANS and the Large Eddy Simulation methods to study the Sandia flame D experiment. Four regimes of the gas burner, differing by thermal power, are studied experimentally and numerically, comparing measured and computed flue gas temperature and emissions. The flow features leading to NOx formation are analyzed. At low power, most NOx formation occurs in the flame core, where temperatures are highest. At high power, a significant amount of NOx forms where a secondary stream of oxidizer meets the high-temperature burnt gas stream. The NOx formation rate is modeled either by summing the contributions of the main paths relevant to the studied problem or via two variants of the FGM scalar transport approach. One of these variants features a correction to the transported scalar approach that enables accounting for the effects of non-adiabatic phenomena, e.g. heat radiation, on NOx formation without increasing the look-up table dimensionality and the required memory usage. The correction is shown to improve emission predictions over the baseline model, although quantitative differences between predicted and measured emission levels remain significant. The approach computing the NOx formation rate as by summing contributions yields the best agreement with measurements when the thermal path predominates, and the formation of nitrogen dioxide is negligible.

A viscous investigation on the hydrodynamic coefficients and wave loads under the interaction of side-by-side cylinders in regular waves

The paper introduces a two-dimensional Reynolds-Averaged Navier-Stokes Computational Fluid Dynamics (RANS CFD) model to investigate the effects of adjacently floating bodies on the hydrodynamic coefficients and wave loads acting on these bodies. The analysis considers two square cylinders with a narrow gap in way of the free water surface. The physical significance of subsections of the hydrodynamic coefficient matrix becomes evident when comparing coefficients obtained from oscillating-oscillating versus oscillating-fixed models. This understanding is significant, particularly in applications where only specific portions of the hydrodynamic coefficient matrix are utilized, such as in ship-ice collision scenarios (Jiang et al., 2023a). The correlation between wave loads and wave elevations reveals that the sway force and roll moment are associated with the disparity in wave elevation at both sides of each cylinder, while heave forces correlate with the averaged wave elevation on both sides of each cylinder. It is concluded that hydrodynamic interactions are sensitive to the displacement of a floater and accordingly can dominate added mass and damping effects.

Characterization of Out-of-Plane Curved Fluidic Oscillators

A novel fluidic oscillator design, in which the oscillator is curved along the primary flow direction, was evaluated. The effects of mass flow rate, hydraulic diameter, aspect ratio, curvature radius, surface roughness, inlet orientation, and nonconstant curvatures were experimentally investigated. Measurements of the oscillation Strouhal number, discharge coefficient, spreading angle, and sweeping angle were used to characterize the jet. The resulting oscillators were found to fall into one of three categories: oscillated at the same frequency and sweep angle as conventional flat oscillators; oscillated at a slightly higher frequency and lower sweep angle than flat oscillators; or no dominant oscillation frequency detected and with no sweeping action. An unsteady Reynolds-averaged Navier–Stokes computational fluid dynamics simulation revealed fundamental differences in the internal flow mechanisms between flat and curved oscillators that drive the sweeping jet. The curvature between 37.5 and 62.5% of the total length, or the region from the inlet nozzle to halfway through the main chamber, was a primary factor influencing the response type of a design. Due to the curvature of these oscillators, they have the ability to be used in geometrically constrained spaces, such as the leading edge of wings and turbine vanes.

Hypersonic FLEET velocimetry and uncertainty characterization in a tripped boundary layer

Femtosecond laser electronic excitation tagging (FLEET) velocimetry is applied in a hypersonic boundary layer behind an array of turbulence-inducing trips. One-dimensional mean velocity and root-mean-square (RMS) of velocity fluctuation profiles are extracted from FLEET emissions oriented across a 2.75∘ wedge and through a boundary layer above a flat plate in two test campaigns spanning 21 tunnel runs. The experiment was performed in the Texas A&M University Actively Controlled Expansion tunnel that operated near Mach 6.0 with a Reynolds number near 6 × 106 m−1 and a working fluid of air at a density near 2.5 × 10−2 kg m−3. Detailed analysis of random and systematic errors was performed using synthetic curves for error in the mean velocity due to emission decay and the error in the RMS velocity fluctuation due to random error. The boundary layer behind an array of turbulence-inducing trips is documented to show the breakdown of coherent structures. FLEET velocimetry is compared to the tunnel Data Acquisition System, Vibrationally Excited Nitric Oxide Monitoring results, and Reynolds-Averaged Navier–Stokes computational fluid dynamics to verify results.

Computational Fluid Dynamics Turbulence Model and Experimental Study for a Fontan Cavopulmonary Assist Device.

Head-flow HQ curves for a Fontan cavopulmonary assist device (CPAD) were measured using a blood surrogate in a mock circulatory loop and simulated with various computational fluid dynamics (CFD) models. The tests benchmarked the CFD tools for further enhancement of the CPAD design. Recommended Reynolds-Averaged Navier-Stokes (RANS) CFD approaches for the development of conventional ventricular assist devices (VAD) were found to have shortcomings when applied to the Fontan CPAD, which is designed to neutralize off-condition obstruction risks that could contribute to a major adverse event. The no-obstruction condition is achieved with a von Karman pump, utilizing large clearances and small blade heights, which challenge conventional VAD RANS-based CFD hemodynamic simulations. High-fidelity large eddy simulation (LES) is always recommended; however, this may be cost-inhibitive for optimization studies in commercial settings, thus the reliance on RANS models. This study compares head and power predictions of various RANS turbulence models, employing experimental measurements and LES results as a basis for comparison. The models include standard k-ϵ, re-normalization group k-ϵ, realizable k-ϵ, shear stress transport (SST) k-ω, SST with transitional turbulence, and Generalized k-ω. For the pressure head predictions, it was observed that the standard k-ϵ model provided far better agreement with experiment. For the rotor torque, k-ϵ predictions were 30% lower than LES, while the SST and LES torque values were near identical. For the Fontan CPAD, the findings support using LES for the final design simulations, k-ϵ model for head and general flow simulation, and SST for power, shear stress, hemolysis, and thrombogenicity predictions.

Aerodynamic Modeling of a Flying Wing Featuring Ludwig Prandtl’s Bell Spanload

This paper presents the aerodynamic modeling of a flying wing featuring Ludwig Prandtl’s bell spanload. The aerodynamic models are developed using a medium fidelity vortex-lattice method and using a Reynolds-Averaged Navier–Stokes computational fluid dynamics solution across a wide range of in-flow angle conditions. A methodology is developed to directly compare the spanwise force distributions from each method. Excellent agreement is seen in the prediction of spanwise inertial aerodynamic forces from each method, as well as in stability and control derivatives dominated by lift and moment contributions. The phenomenon of proverse yaw, caused by the twist distribution necessary to produce the bell spanload, is seen in the high and low-order analysis, with similar off-axis control power predicted.

Assessment of advanced RANS turbulence models for prediction of complex flows in compressors

Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) has been widely used in compressor design and analysis. However, reasonable prediction of compressor flow and its impact on compressor performance remains challenging. In this study, Menter’s Shear Stress Transport (SST) model and its variants, as well as the ω-based Reynolds stress model (Stress-BSL) are assessed. For a single rotor (Rotor 67), under the peak efficiency operating condition, all studied turbulence models predict its performance with reasonable accuracy; under the off-design conditions, SST with Helicity correction (SST-Helicity) shows superiority in predicting the effect of flow on the spanwise distribution of aerodynamic parameters. For Darmstadt’s 1.5-stage transonic axial compressor, SST-Helicity outperforms SST, SST with the Quadratic Constitutive Relation (SST-QCR) and Stress-BSL in predicting the performance as well as the spanwise distribution of aerodynamic parameters. At the design rotating speed, the stall margin given by SST-Helicity (20.90%) is the closest to the experimental measurement (24.81%), which is more than twice that by SST (8.71%) and 1.5 times that by SST-QCR (14.14%). This paper demonstrates that SST-Helicity model, together with a good quality and sufficiently refined grid, can capture the compressor flow features with reasonable accuracy, which results in a credible prediction of compressor performance and stage matching.

Interaction Mechanism of Transonic Squealer Tip Cooling With the Effect of High-Speed Relative Casing Motion

Abstract The relative casing motion can significantly influence the turbine blade tip aerothermal performance. In this study, experimental investigation was conducted in a newly developed high-speed disk rotor rig which can mimic engine realistic high-speed casing relative motion while enabling full optical access to a transonic turbine blade tip surface. Spatially-resolved tip heat transfer data, including heat transfer coefficient and film cooling effectiveness, were obtained for a cooled transonic squealer tip by infrared transient thermal measurement. Combined with closely coupled Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) analysis, this paper reveals an interesting interaction mechanism between the cooling injections from the pressure side and the cavity floor with and without the effect of relative casing motion. Both experimental data and CFD results show a consistent trend in both heat transfer and cooling performance. With cavity cooling only, the cooling performance reduces with the effect of relative casing motion. However, with additional cooling injection from the pressure side, a significant improvement in the combined cooling performance with the relative casing motion can be observed. Such opposite trend highlights the importance of relative casing motion when ranking different tip cooling designs. With the consideration of relative casing motion, extra tip cooling benefit can be obtained by combining cooling injections from two different locations.

The Effect of a Linear Free Surface Boundary Condition on the Steady-State Wave-Making of Shallowly Submerged Underwater Vehicles

Near-surface simulation methods for shallowly submerged underwater vehicles are necessary for the population of a variety of free-surface-affected, coefficient-based maneuvering and seakeeping models. Simulations vary in complexity and computational costs, often sacrificing accuracy for simplicity and speed. One particular simplifying assumption, the linearization of the free surface boundary conditions, is explored in this study by comparing the steady-state wave-making characteristics of a shallowly submerged prolate spheroid using two different simulation methods at several submergence depths and forward speeds. Hydrodynamic responses are compared between a time-domain boundary element method that makes use of a linearized free surface boundary condition and an inviscid, volume of fluid Reynolds-Averaged Navier–Stokes computational fluid dynamics code that imposes no explicit free surface boundary condition. Differences of up to 22.6%, 32.5%, and 33.3% are found in the prediction of steady state surge force, heave force, and pitch moment, respectively. The largest differences between the two simulation methods arise for motions occurring at small submergences and large wave-making velocities where linear free-surface assumptions become less valid. Nonlinearities that occur in such cases are revealed through physical artifacts such as wave steepening, wave breaking, and high-energy waves. A further examination of near-surface viscous forces reveals that the viscous drag on the vessel is depth dependent due to the changing velocity profile around the body.

Numerical and Experimental Analysis of the Cold Flow Physics of a Nonpremixed Industrial Gas Burner

Abstract The flow field of a nonpremixed industrial gas burner is analyzed with Reynolds-averaged Navier–Stokes computational fluid dynamics validated against velocity and pressure measurements. Combustion is not modeled because the aim is optimizing the predictive capabilities of the cold flow before including chemistry. The system's complex flow physics, affected by a 90 deg turn, backward and forward facing steps, and transversal jets in the mainstream is investigated at full and partial load. The sensitivity of the computed flow field to inflow boundary condition setup, approach for resolving/modeling wall-bounded flows, and turbulence closure is assessed. In the first sensitivity analysis, the inflow boundary condition is prescribed using measured total pressure or measured velocity field. In the second, boundary layers are resolved down to the wall or modeled with wall functions. In the third sensitivity analysis, the turbulence closure uses the k−ω shear stress transport eddy viscosity model or two variants of the Reynolds stress model. The agreement between the predictions of most simulation setups among themselves and with the measurements is good. For a given type of inflow condition and wall flow treatment, the ω-based Reynolds stress model gives the best agreement with measurements among the considered turbulence models at full load. At partial load, the comparison with measured data highlights some scatter in the predictions of different patterns of the flow measurements. Overall, the findings of this study provide insight into the fluid dynamics of industrial gas burners and guidelines for their simulation-based analysis.

High-Fidelity Aerostructural Optimization with a Geometrically Nonlinear Flutter Constraint

When designing aircraft, avoiding dynamic aeroelastic instabilities such as flutter is a key requirement. One way to meet this requirement is to use a multidisciplinary design optimization subject to a flutter constraint. Flutter-constrained design optimizations have used geometrically linear detailed models, which do not accurately predict flutter for very flexible aircraft, or geometrically nonlinear low-order models, which do not accurately trade off cruise range and structural mass. This paper presents a framework for integrating a geometrically nonlinear, subsonic flutter constraint that captures the large in-flight deflections of very flexible aircraft into high-fidelity gradient-based aerostructural optimization. The cruise range and stress constraints are computed accurately with detailed aerostructural analyses, which use a built-up finite element model coupled to Reynolds-averaged Navier–Stokes computational fluid dynamics. The detailed model is condensed to a low-order aeroelastic model to compute the geometrically nonlinear flutter constraint and its adjoint derivatives with computational cost and robustness suitable for optimization. The framework is demonstrated by maximizing the cruise range of a subsonic high-aspect-ratio wing with respect to panel thicknesses, sweep, and span. The impact of the geometrically nonlinear flutter constraint highly depends on the in-flight deformation level. At low deflection levels, sweeping the wing backward is the most effective flutter prevention method, and the flutter constraint has little impact on the achievable cruise range. At high deflection levels, shortening the wing span is necessary to suppress flutter, reducing the achievable cruise range by up to 5.9%. This work is a step toward making multidisciplinary design optimization a practical tool for designing the energy-efficient, very flexible aircraft of the future, which require geometrically nonlinear flutter analyses early in the design cycle to prevent flutter.

A Review of Solution Stabilization Techniques for RANS CFD Solvers

Nonlinear, time-linearized and adjoint Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) solvers are widely used to assess and improve the aerodynamic and aeroelastic performance of aircrafts and turbomachines. While RANS CFD solver technologies are relatively mature for applications at design conditions where the flow is benign, their use in off-design conditions, featuring flow instabilities, such as separations and shock wave/boundary layer interactions, still faces many challenges, with tight residual convergence being a major difficulty. To cope with this, several solver stabilization techniques have been proposed. However, a systematic and comparative study of these techniques has not been reported, to some extent hindering the wide deployment of these methods for industrial applications. In this paper, we critically review the existing methods for solver convergence stabilization, with the main purpose of explaining the rationale behind the algorithms and providing a systematic view of the seemingly different methods. Specifically, mathematical formulations and implementation details of these methods, example applications, and the pros and cons of the methods are discussed in detail, along with suggestions for further improvements. This review is expected to give CFD method developers an overview of the various solution stabilization methods and application engineers an idea how to choose a suitable method for their respective applications.

ДОСЛІДЖЕННЯ МОРЕХІДНОСТІ РИБАЛЬСЬКИХ СУДЕН ЗА ДОПОМОГОЮ CFD МЕТОДІВ

Seakeeping performance is quite important for certain ship types. Fishing vessels often operate in areas with frequent storms, and sometimes it is necessary to continue fishing despite the worsening sea state. The development of hull forms providing good seakeeping performance of fishing vessels is the problem of current interest in ship design. The conventional approach to seakeeping studies is testing models in ship model basins. However, it is time-consuming and expensive, especially when many hull form variants are studied. For this reason, computer calculations based on the theory of ship motions and strip theory were developed and introduced. Today the more advanced methods of computational fluid dynamics (CFD) can be applied to the problem. The study of ship motions with the help of Reynolds-averaged Navier-Stokes (RANS) CFD method is considered in this paper. A suggested numerical model implies the generation of waves through initial and boundary conditions, which express fully developed waves with preset parameters. An object of research is the seagoing trawler with an overall length of 44.6 m. Three versions of hull form are used in simulations. All versions have similar transom afterbodies, but different forebodies: one similar to Axe Bow, a bulbous bow and one similar to X-bow. Ship movement with headings 180° and 150° at speed of 3.5 knots was studied to reveal differences in added resistance and ship motions. While added resistance and characteristics of heaving and pitching have shown no clear advantages among the considered shapes of forebodies, the version similar to X-bow has demonstrated a significant decrease in rolling at heading 150°. The results of the study have shown that the suggested numerical setup in combination with the CFD methods described can be used for quite realistic simulations of ship behaviour in rough seas. Keywords: seakeeping simulations, seakeeping of fishing vessels, CFD for ship design, improved seakeeping performance, simulation of ship motions.

Surrogate Model Development for Optimized Blended-Wing-Body Aerodynamics

In the conceptual design phase of conventional-configuration aircraft, calibrated low-fidelity methods provide sufficiently accurate estimates of aerodynamic coefficients. It has been observed, however, that for blended-wing–body aircraft, important flow effects are not captured adequately with low-fidelity aerodynamic tools. Consequently, high-fidelity methods become necessary to study blended-wing–body aerodynamics. Since repeated function calls are needed in an optimization loop, high-fidelity analysis is prohibitively expensive in the conceptual design phase, where several optimization scenarios are considered. In this paper, the integration of high-fidelity data for blended-wing–body aircraft for a mission calculation module is presented. A surrogate model based on Gaussian processes (GPs) with acceptably low prediction error is sought as an alternative to Reynolds-averaged Navier–Stokes computational fluid dynamics. Three adaptations are considered: sparse GPs, mixtures of GP approximators, and need-based filtering for GP. The results provide benchmark values for this case and show that the combination of subsonic and transonic behaviors in the training set is problematic and that, for the considered datasets, sparse GP models suffer from oversmoothing, while mixtures of GP models suffer from overfitting. From the error levels, it is observed that a GP with an infinitely differentiable squared exponential kernel based on reduced data pertinent to mission analysis is the most effective option.

A parametric study on the hydrodynamics of tidal turbine blade deformation

The blades of axial-flow rotors, which are typically made of flexible composite materials, can experience significant deformations through their operation. However, the impact of these deformations on rotor hydrodynamics is not well understood. Blade deformations can be separated into three main components: flapwise, a thrust-driven deformation in the direction of the flow; edgewise, relatively small deformations in the plane of rotor motion and driven by rotor torque; and twist deformations that affect each blade’s angle of attack distribution and are generated by the torsional moment acting about the blade’s spanwise axis as well as by structural interactions. This work evaluates the hydrodynamic effects of the decoupled flapwise and twist deformations on a tidal turbine blade, using blade-resolved Computational Fluid Dynamics (CFD) simulations with the objective of identifying and quantifying the associated flow phenomena. The deformation cases were generated by scaling the static deformation shapes from a structural model of the turbine blade. The dataset used in this work, part of a larger research project, consists of 48 blade-resolved Reynolds-Averaged Navier–Stokes CFD steady-state simulations. It was found that twist deformation effects are significant, and can be adequately described using blade element theory. Flapwise deformations, on the other hand, produce different phenomena affecting the rotor loading and performance in ways that cannot be explained on a blade sectional basis through blade element theory. It is found that the hydrodynamic impact of flapwise deformations can be explained through two different mechanisms: a pressure drop on the suction side of the blade that generates inboard load augmentation, and an increase in near-tip radial flow effects that moves the onset of tip-loss effects, and shedding of thrust and power, further inboard. The studied cases show a significant impact of flapwise deformation on integrated power (up to a 20% drop), while the impact on integrated thrust remains limited, with variations between -4% to +2% in thrust coefficient observed depending on blade bending.

Experimental and numerical investigation of wall temperature in a heated pipe filled with beads

Placing granular materials inside empty channels with coolant or heat transfer fluids flowing through is an effective way to increase the heat transfer rate to the wall. Although this approach has been used in different engineering fields, a particular goal is seldom considered in some applications, namely the temperature uniformity of the bounding wall. As temperature varies along the flow direction, a non-uniform temperature field appears on the wall. This bears consequences in some applications such as in electronics, battery cooling or composite manufacturing. In the present study, the uniformity of the wall temperature is investigated numerically for a typical cylindrical pipe filled with monodisperse ceramic beads and heated by air flow. Numerical simulations based on Reynolds-averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) are performed to analyze the heat transfer to the bounding wall. Because of the uncertainty mentioned in the literature, the applicability of an empirical model reflecting additional sources of production and dissipation of turbulent energy due to beads is firstly evaluated. By comparing the numerical predictions of temperature fields with experimental data, a damping function is needed to adjust these additional source terms to better fit experimental data for bulk Reynolds numbers between 100 and 700. A parametric study is then conducted to assess the effect of various parameters on the wall temperature uniformity. Results shows that wall materials of low volumetric heat capacity and a reduced wall thickness greatly shorten the duration to reach thermal uniformity. A less pronounced enhancement also exists for larger thermal conductivity of the wall material. However, using beads of lower volumetric heat capacity does not have a major influence on the uniformity of the wall temperature.