A data–driven sensibility tool for flow control based on resolvent analysis

Abstract

Transient growth and resolvent analyses are routinely used to assess nonasymptotic properties of fluid flows. In particular, resolvent analysis can be interpreted as a special case of viewing flow dynamics as an open system in which free-stream turbulence, surface roughness, and other irregularities provide sources of input forcing. We offer a comprehensive summary of the tools that can be employed to probe the dynamics of fluctuations around a laminar or turbulent base flow in the presence of such stochastic or deterministic input forcing and describe how input–output techniques enhance resolvent analysis. Specifically, physical insights that may remain hidden in the resolvent analysis are gained by detailed examination of input–output responses between spatially localized body forces and selected linear combinations of state variables. This differentiating feature plays a key role in quantifying the importance of different mechanisms for bypass transition in wall-bounded shear flows and in explaining how turbulent jets generate noise. We highlight the utility of a stochastic framework, with white or colored inputs, in addressing a variety of open challenges including transition in complex fluids, flow control, and physics-aware data-driven turbulence modeling. Applications with temporally or spatially periodic base flows are discussed and future research directions are outlined.

Convective heat transfer during laminar fluid flow through channels is an important technological problem. The literature provides much research data on heat transfer phenomena occurring during fluid flow through channels of different dimensions and shapes based on theoretical analysis, numerical calculations and experimental investigations. Theoretical analysis has attempted to solve the problem of convective heat transfer in channels of basic shape in simplified conditions of fluid flow. Laminar convective heat transfer in pipes where the fluid velocity profile was parabolic was described by Graetz (Graetz, 1885). His solution to this classical problem was further developed by Sellars, Tribus and Klein (Sellars et al., 1956). Alternatively, Levěque (Levěque, 1928) investigated heat transfer in the entrance region of pipes where hydraulic stabilisation occurs. All these works offer an analytical solution to the problem. Numerical investigation of heat transfer in the entrance region of pipes was initiated by Kays (Kays, 1955) who provided the results of numerical calculations for three types of gas flow conditions: uniform wall temperature, uniform heat flux and uniform difference between wall and fluid temperature. On the other hand, the work of Sider and Tite (Sider and Tite, 1936) is an example of an early experimental investigation where an empirical formula for the heat transfer coefficient calculations, regardless of the fluid being heated or cooled, is provided. The above-mentioned works were followed by further research on the laminar convective fluid flow in channels. Particularly, heat transfer in channels of small hydraulic diameters was extensively investigated. It turned out that heat transfer and fluid flow in small diameter channels often differed from those in channels of conventional dimensions. Mathematical equations describing heat transfer cannot always be applied to minior microchannels. Hence some researchers (Adams et al., 1998), (Tso and Mahulikar, 2000), (Owhaib and Palm, 2004), (Lelea et al., 2004), (Celata et al., 2006), (Kandlikar et al., 2006), (Yang and Lin, 2007), (Yarin et al., 2009) examined liquid and gas convective heat transfer in circular miniand micro-channels using experimental methods, mostly the thermal balance method. However, the surface and fluid temperature measurements using this method are difficult to obtain due to the small size of the channels tested. Application of mass transfer investigations and the mass/heat transfer analogy makes it possible to avoid the problem as it excludes temperature measurements. In this chapter application of the mass/heat transfer

Influence of metal foam thickness on the conduction and convective heat transfer for a flat plate with metal foam impinged by a rectangular slot jet

Chemical reaction, Dufour and Soret effects on the stability of magnetohydrodynamic blood flow conveying magnetic nanoparticle in presence of thermal radiation: A biomedical application

High pressure/high temperature forced and mixed convection experiments have been performed with helium and nitrogen at temperatures and pressures up to 893 K and 64 bar, respectively. The test section had a 16.8 mm ID flow channel in a 108 mm OD graphite column. Flow regimes included turbulent, transitional, and laminar flows with the inlet Reynolds numbers ranging from 1500 to 15,000. Due to strong heating, the local Reynolds number decreased by up to 50% over the 2.7 m test section. In addition, heat transfer degradation and flow laminarization caused by intense heating led to Nusselt numbers 20–50% lower than the values given by the modified Dittus–Boelter and modified Gnielinski correlations. Flow laminarization criteria were considered based on a dimensionless acceleration parameter (Kv) and buoyancy parameter (Bo*). Upward turbulent flows displayed higher wall temperatures than downward flows, due to the impact of flow laminarization which is not expected to affect buoyancy-opposed flows. Laminar Reynolds number flows presented an opposite behavior due to the enhancement of heat transfer for buoyancy-aided flows. At low Reynolds numbers, downward flows displayed higher and lower wall temperatures in the upstream and downstream regions, respectively, than the upward flow cases. In the entrance region of downward flows, convection heat transfer was reduced due to buoyancy leading to higher wall temperatures, while in the downstream region, buoyancy-induced mixing caused higher convection heat transfer and lower wall temperatures.

Analyses of coupled steady heat transfer processes with entropy generation minimization and entransy theory

Laminar convective heat transfer of Al2O3/water nanofluid through square cross-sectional duct

Research on the audible acoustic field-enhanced heat transfer of double-pipe exchangers: Effect of laminar flow and turbulence, vertical and horizontal placement of pipes

An experimental investigation was carried out to study the influence of pulsation and special surface geometry on the convective heat transfer in laminar flow. The experiments were performed using a glycerol-water mixture of 23 wt% glycerol. Ethanol was used as a coolant. The amplitude of pulsation was between 0.37 and 0.91 mm and the frequency range was 26.7 to 42.7 Hz. The mean flow Reynolds number range was between 50 and 1143. All the geometrical parameters of the channel such as the relative fin spacing and relative fin thickness were constant. The enhancement factor E, i.e. the ratio of heat transfer coefficient due to pulsation compared to steady flow diminishes at low Pe. A maximum E was observed in medium ranges of Pe and small Pe. The amount of heat transferred from the working fluid also depends on κ value. So far, a maximum heat transfer enhancement of E = 2.5 at κ = 3 and Pe = 2750 was obtained. The enhancement factor also increases with increasing pulsation amplitude.

Due to the low performance observed during natural convection with fluids such as air and water, nanofluid research was carried out to analyse them for convective heat transfer applications. Heat transfer comparison between water and different water-based nanofluids comprising of MWCNT, alumina and silver has been established for Rayleigh Number 1.5 × 109. Numerical analysis of 2-D differentially heated square cavity has been performed under turbulent natural convection. The top and bottom walls are considered to be at constant temperatures, while the side walls are adiabatic in nature. Based on previous research, nanofluid volume concentration of 0.1 vol% has been considered for this study, and the nature of flow physics and natural convection heat transfer has been explored. It is observed that multiple vortices (almost similar size) exist and evenly speared within the computational domain for air. The viscosity of the fluid was observed to be a deciding factor for the degree of turbulence, thickness and velocity variations within the boundary layer. The average fluid velocity and vortex circulation strength are highest for alumina nanofluid and least for water. The other two nanofluids lie in between with the velocity and vorticity variations of 12.8 and 16.5%, respectively. In terms of heat transfer, alumina nanofluid performs admirably well, followed by MWCNT nanofluid with a variation in radiation heat transfer of 60.8 and 53.19% when compared to air, while for convective heat transfer the variation observed was 98.4 and 97.8%, respectively. Due to the high densities of these nanofluids as compared to air, achieving thermal stratification is difficult. Alumina nanofluid performs admirably well in enhancing convection and radiation heat transfer.

Modeling heat transfer in packed bed processes such as iron ore pelletization is essential for optimizing process operation and furnace design. In these systems, materials like magnetite iron ore undergo thermal and chemical transformations, where heat and mass transfer are often coupled with heat effects from multiple processes — including both exothermic chemical reactions (e.g., oxidation) and endothermic physical changes (e.g., drying and sintering). As the industry moves towards fossil-free ironmaking, it becomes increasingly important to isolate pure heat transfer behavior, independent of chemical reactions, to support the development of sustainable process schemes. This study investigates convective heat transfer in a packed bed by evaluating several established correlations against the conventionally used modified Ranz–Marshall correlation. Pilot pot-scale experiments were performed by isothermally heating 120 kg of already indurated iron ore pellets at 300 °C to avoid chemical reactions, with additional experiments at 500 °C and 700 °C to assess performance at elevated temperatures typical of industrial pelletization. Results show that the modified Ranz–Marshall correlation underpredicts heat transfer rates under conditions isolating convective heat transfer, reinforcing the need for this investigation. The Wakao–Funazkri and Rowe–Claxton correlations provided the best agreement with experimental data, particularly at 300 °C. Minor deviations at higher temperatures suggest the influence of unaccounted variables, warranting further study. Sensitivity analysis identified gas velocity as the most significant parameter affecting heat transfer. The results suggest that adopting the Wakao–Funazkri and Rowe–Claxton correlations can provide a stronger basis for predictive pellet heat transfer modeling in future process design and simulation work. • Heat transfer models validated for packed beds at 300, 500 and 700 °C. • Rowe–Claxton and Wakao–Funazkri models provide the most accurate predictions. • Modified Ranz–Marshall model deviates more due to simplified porosity scaling. • Gas velocity strongly affects heat transfer; a 10% reduction improves model accuracy. • Temperature-dependent heat capacity enhances agreement between simulations and experiments. • Discrepancies at high temperatures suggest heat losses and non-uniform porosity effects.

Fluidized bed heat treating systems have been used to heat treat low carbon steel wires for a number of years. Extending this application to high carbon steel wires and metal straps has been implemented with very little success due to the lack of knowledge of heat transfer coefficients or, alternatively, Nusselt number for small cylinders and flat strips. The objective of this study was to provide reliable data for predicting a suitable Nusselt number for small horizontal cylinders and flat strips at various orientations under conditions typically encountered in heat treating fluidized bed systems. In this study, resistively heated small cylinders and flat strips ranging in diameter from 1.27 to 9.53mm and in width from 6.25 to 25.4mm respectively were immersed in a 311mm in diameter lab-scale fluidized bed. The bed consisted of fine alumina oxide sand of mean particle size ranging from 145 to 330[micro]m fluidized by air at ambient temperatures. The fluidized bed unit was capable of fluidizing rates ranging from 0.14 to 23 G/Gmf. The cylinder and flat strip samples were positioned horizontally in the bed. The flat strip samples were rotated around the length's center axis in 15° increments from a 0° horizontal position to a 90° vertical position. The results showed that published correlations over-predict small cylinder Nusselt numbers over the entire fluidizing range; furthermore, their trends did not agree. Flat strip results demonstrated highest heat transfer rates at a vertical position. A correlation that predicts the mean Nusselt number within ±15% for both geometries was developed for operating conditions covered by the experiments.

The significant research has seen with nano fluid flow and heat transfer. But still there is a wide scope of research in mass transfer with nano fluids due to Brownian motion of particles. A theoretical investigation has attempted in this paper to study the chemical reaction effects during mass transfer. We have studied convective heat and mass transfer of MHD nano fluid flow past inclined, oscillating permeable flat plate with radiation and Abstract: The significant research has seen with nano fluid flow and heat transfer. But still there is a wide scope of research in mass transfer with nano fluids due to Brownian motion of particles. A theoretical investigation has attempted in this paper to study the chemical reaction effects during mass transfer. We have studied convective heat and mass transfer of MHD nano fluid flow past inclined, oscillating permeable flat plate with radiation and Abstract: The significant research has seen with nano fluid flow and heat transfer. But still there is a wide scope of research in mass transfer with nano fluids due to Brownian motion of particles. A theoretical investigation has attempted in this paper to study the chemical reaction effects during mass transfer. We have studied convective heat and mass transfer of MHD nano fluid flow past inclined, oscillating permeable flat plate with radiation and

We reveal the effects of sweep on the wake dynamics around NACA 0015 wings at high angles of attack using direct numerical simulations and resolvent analysis. The influence of sweep on the wake dynamics is considered for sweep angles from $0^\circ$ to $45^\circ$ and angles of attack from $16^\circ$ to $30^\circ$ for a spanwise periodic wing at a chord-based Reynolds number of $400$ and a Mach number of $0.1$ . Wing sweep affects the wake dynamics, especially in terms of stability and spanwise fluctuations with implications on the development of three-dimensional (3-D) wakes. We observe that wing sweep attenuates spanwise fluctuations. Even as the sweep angle influences the wake, force and pressure coefficients can be collapsed for low angles of attack when examined in wall-normal and wingspan-normal independent flow components. Some small deviations at high sweep and incidence angles are attributed to vortical wake structures that impose secondary aerodynamic loads, revealed through the force element analysis. Furthermore, we conduct global resolvent analysis to uncover oblique modes with high disturbance amplification. The resolvent analysis also reveals the presence of wavemakers in the shear-dominated region associated with the emergence of 3-D wakes at high angles of attack. For flows at high sweep angles, the optimal convection speed of the response modes is shown to be faster than the optimal wavemakers speed suggesting a mechanism for the attenuation of perturbations. The present findings serve as a fundamental stepping stone to understanding separated flows at higher Reynolds numbers.