Increase In Wall Temperature Research Articles

Research on Safety of Aero-Engine Oil Pipe Under Heating Conditions Based on Fluid–Solid Thermal Coupling

This paper examines the safety of aero-engine pipelines under different heating conditions. Based on the fire test standard documents, a model of an aero-engine oil pipe was constructed, and its safety under heating conditions that meet the standard was analyzed using fluid–solid thermal coupling. The pipe material was stainless steel 1Cr18Ni9Ti, and the oil inside the pipeline was China RP-3 kerosene. To simulate the different working conditions or pump failure scenarios, various kerosene inlet flow rates were used for the calculations. The results indicate that the pipe wall exhibits an uneven temperature distribution under standard heating conditions. As the kerosene flow rate decreases, the pipe wall temperature rises, and heat transfer deterioration occurs. The increase in the pipe wall temperature reduces the material’s strength, while the uneven temperature distribution generates thermal stress, further increasing the safety risk. When the kerosene flow rate is reduced to a certain level, the equivalent stress in the pipe wall exceeds the material’s yield strength, leading to a high risk of rupture.

Effects of wall heating on wall pressure fluctuations and flow noise in a low-Reynolds-number turbulent channel flow with temperature-dependent viscosity

Wall pressure fluctuations and flow noise substantially degrade sonar detection performance and the acoustic stealth performance of underwater vehicles. This paper numerically investigates the effects of wall heating on wall pressure fluctuations in turbulent channel flow of water with temperature-dependent viscosity, exploring a novel method for controlling wall pressure fluctuations and flow noise in underwater vehicles. Large-eddy simulation (LES) is employed for the numerical calculation of the flow field, while a hybrid method combining LES with Lighthills acoustic analogy is employed to predict flow noise. The numerical results show that when the temperature difference between the wall and the incoming flow is 30 K and 50 K, the peak root-mean-square pressure fluctuations decrease by 6.76% and 8.91%, respectively. Wall heating stabilizes the pressure field near the wall, with the spectral levels of wall pressure fluctuations showing average decreases of approximately 1 dB and 2 dB. Wall heating weakens the energy-containing structures of wall pressure fluctuations and increases the overall convection velocity by 1.22% and 3.81%, respectively. Flow structure analysis reveals that the weakening of energy-containing structures results from the suppression of the vortex structures in the near-wall region. In the wall heating cases, peak turbulent kinetic energy decreases by 12.6% and 15.8%, respectively. Moreover, the sound pressure level of flow noise decreases with increasing wall temperature, with the maximum noise reduction exceeding 3 dB. Previous studies have not yet explored the effects of viscosity reduction caused by wall heating on wall pressure fluctuations and flow noise. This study demonstrates that wall heating is a promising method for reducing wall pressure fluctuations and flow noise.

A novel contact thermal resistance model for heat transfer in granular systems: Leveraging the force-heat analogy

A novel particle-to-particle contact thermal resistance model is proposed in this study, based on the concept of analogy between force and heat transfer. The distribution of heat flux on the contact surface is assumed to resemble the distribution of stress, eliminating the issue of temperature singularity at the contact edge. The model is validated against existing theories and experiments, showing good agreement. The combined use of the model and the thermal discrete element method is applied to analyze temperature and effective thermal conductivity distributions in a pebble bed within a high-temperature test unit. The average effective thermal conductivity obtained from thermal conduction is found to be 2.99 and 2.61 W/(m·K) for power inputs of 20 kW and 82 kW, respectively. An increase in the outer wall temperature from 200 °C to 1000 °C results in an approximate 20 % increase in the effective thermal diffusivity.

Quantifying the effects of inlet gas and collision models in direct metal deposition using a CFD-DEM approach

Simulations of the powder jet in direct metal deposition (DMD) are often made with significant simplifications such as being incompressible, steady-state, or single-component, and do not provide explanation for the choice of parameters in the collision model. This work presents a coupled Computational Fluid Dynamics–Discrete Element Method model for the powder jet in DMD that considers all of the following features: compressibility effects, particle–wall and particle–particle collisions, turbulence, gas mixing, and melt pool boundaries. The goal of the simulation is to optimize the operating conditions and to predict the outcomes of experiments. After effective validation against experimental results, the effects of inlet gas, collision models and different boundary conditions in DMD have been comprehensively studied. It is demonstrated that gases with higher diffusivities, such as helium, are less effective shielding gases than those with lower diffusivities, such as argon. The increased wall temperature arising from the melt pool and track has little influence on the particle distribution.

Numerical simulation of premixed n-heptane/air combustion in micro tube with internal channel optimization

In military and aerospace fields, petrol and aviation kerosene are the preferred fuels for micro power systems due to their reduced carrying load and convenient fuel source. Therefore, n-heptane, an alternative to petrol and aviation paraffin, was chosen as the fuel. A micro quartz glass tube was used as the combustor, and the premixed combustion characteristics of n-heptane/air were investigated using numerical simulations. The method used to improve the internal flow channel includes a built-in cross baffle and scaled backward-facing step. The resulting optimized combustion characteristics, such as internal flow line, wall temperature, CO emission, and wall radiation, have been analyzed. The results indicate that, with a fixed equivalence ratio of 1.0 and a n-heptane mass flow rate of 2.70 mg/s, the built-in cross baffle concentrates and stabilizes the high temperature zone of the flame, resulting in a significant increase in wall temperature. Conversely, the use of the micro tube with scaled backward-facing step creates a reflux zone due to the sudden expansion of the inlet cross-section, which promotes better fuel mixing and flame anchoring. Furthermore, after comparing the output efficiencies of micro tube with different internal structures, it was discovered that enhancing the internal channel of the micro tube is crucial for increasing the wall radiation efficiency.

Study on the flow boiling characteristics of novel pin fin heat sinks in a two-phase mechanically pumped cooling loop

As a new thermal control technology, a two-phase mechanically pumped cooling loop (MPCL) holds promise in addressing cooling issues of avionics. The heat sinks in MPCL can remove heat from avionics to refrigerant. Since previous research focused primarily on conventional heat sinks, three novel pin fin heat sinks (PFHSs) were investigated based on an MPCL. With increasing heat flux, heat transfer coefficient (HTC) and frictional pressure drop (FPD) increase. With the inlet state from subcooled to saturated and then to two-phase, HTC and FPD increase. Increasing inlet saturation temperature yields an increase in HTC and heating wall temperature (Tw). An increase in flow rate inhibits heat transfer deterioration while inducing significant growth in FPD. When heat flux is below 150 kW/m2, the petaloid I PFHS has the best temperature control performance, while the honeycombed PFHS has the best FPD. When heat flux exceeds 150 kW/m2, HTC decreases rapidly after reaching the peak. Increasing average vapor quality leads to a slight decrease in Tw but an increase in FPD. When heating load is started, flow rate decreases and Tw and pressure drop increase significantly, but they can gradually stabilize. These findings have significant implications for optimizing the MPCL.

Experimental research on high-temperature radiation characteristics of film-cooled plate of gas turbines

With the rise in pre-turbine temperature and advancements in cooling technology, the temperature gap between the hot-gas and the blades increases. This phenomenon accentuates the significance of high-temperature radiation. However, the relevant experiments available to provide quantitative assessments of radiation are limited because of the challenging task of designing, constructing, and operating a high-temperature radiation facility. In this study, a high-temperature radiation facility is constructed to study the measurement method of evaluating radiation. The radiative heat flux of film-cooled plate of gas turbines are quantified successfully through the presented infrared-thermocouple dual reference body measurement and regression technique based on thermocouple data. The two proposed methodologies can pave the way for novel research avenues in evaluating radiation of the guide vanes. It is found that the proportion of radiation to total heat flux decreases gradually as the wall temperature increases. When the mainstream temperature is 912 K and the coolant temperature is 303 K, the radiation constitutes 50 % of the total heat flux.

A molecular dynamics study of thin water layer boiling on a plate with mixed wettability and nonlinearly increasing wall temperature

This paper introduces a molecular dynamics investigation of the influence of mixed-wettability on the boiling of a water layer over a flat plate surface with nonlinearly increasing wall temperature. The first-type Dirichlet temperature condition, which is considered for the first time in the analysis of the wettability influence on nucleation and boiling at the atomic scale, is consistent with the case of irradiation from photons, plasma, or high-temperature gas molecules. The simulation of the density evolution of water molecules in the nucleation zone shows that the surface with an optimal proportion (60 %∼70 %) of hydrophilic walls is most efficient for nucleation on the studied mixed-wettability substrates, attributing to the increased surface potential energy on the walls. Compared to the hydrophilic or hydrophobic surfaces, the mixed-wettability surfaces transfer more energy from the wall to the liquid. This is because the hydrophobic portion retards the forming of vapor layer and the hydrophilic portion induces an efficient liquid/solid interaction, with a lowered interfacial heat resistance and promoted nucleation. The results also indicate that there exists an appropriate area ratio that is most advantageous for nucleation and boiling intensification under such temperature-increasing boundary conditions. Based on this work, it may be possible to successfully manage boiling at the nanoscale by exploiting the coupled effects of hybrid wettability and irradiation.

A numerical study on premixed laminar ammonia/air flames enriched with hydrogen: An analysis on flame–wall interaction

Ammonia (NH3) has been recognized as a potential carbon-free synthetic fuel of the near future. To enhance its low reactivity, one practical option is to blend it with hydrogen (H2). In this study, the transient head-on quenching of premixed laminar ammonia/air flames enriched with hydrogen is explored based on numerical simulations using detailed chemistry and the mixture-averaged transport model. In this respect, nine different test cases are studied for blending ratios (the molar ratio of hydrogen to the ammonia/hydrogen mixture) of 0.0, 0.2, and 0.4, equivalence ratios of 0.8, 1.0, and 1.2, wall temperatures of 300, 500, and 750 K, and pressures of 1, 2, and 5 atm. The results reveal that the quenching distance (maximum absolute wall heat flux) decreases (increases) with increasing the blending ratio, the equivalence ratio, the wall temperature, and the pressure. For all the test cases, the quenching Peclet number changes between 1 and 3.5. In addition, the local heat release rate enhancement and the role of radical recombination reactions are highlighted at the time of quenching in the vicinity of the wall. This effect is augmented as the blending ratio, the equivalence ratio, and the wall temperature increase. Furthermore, the results show that the N2 pathway is the dominant pathway in consumption of NO near the wall at the time of quenching, in which R76 (NH2+NO⇔N2+H2O) poses the rate controlling role. In addition, the leading role of R85 (NH+NO⇔N2O+H) in consuming NO and converting it to N2O is highlighted at the time of quenching near the wall. Moreover, the significant roles of molecular diffusion and reaction source terms over convection are discussed for both NO and N2O species transport in the vicinity of the wall.Novelty and significance statement: The significance of this work is that using ammonia and its blends with hydrogen as promising carbon-free fuels for the future has several technical issues/uncertainties, which needs to be addressed fundamentally. One of the relatively unexplored issues in the combustion devices for ammonia/hydrogen/air flames is the head-on quenching phenomenon, which is investigated in detail in this study. The novelty of this work is that, for the first time, (1) the head-on quenching of various ammonia/hydrogen blends is systematically studied numerically, employing detailed chemistry, (2) effect of wall on the heat release rate chemistry is discussed wherein the role of radical recombination reactions is highlighted, and (3) the formation pathways of pollutant emissions (NO and N2O) for such flames are thoroughly investigated in the freely propagating flame scenario and in the vicinity of the wall at the time of quenching.

Internal energy distributions of BeH, BeD, and BeT molecules created during chemically assisted physical sputtering in JET tokamak plasma

We present here the results of the spectroscopic analysis of the high-resolution visible spectra of beryllium hydride and its isotopologues (BeH, BeD, and BeT), produced during plasma–surface interactions during limiter and divertor JET-ILW (ITER-like Wall) pulses. The hydride production, being an important part of the wall erosion via chemical-assisted physical sputtering, shows visible dependence on plasma and wall conditions, and also on the isotope content of the plasma. This work shows that this dependence is also true for the molecular energy distributions, parameterized by rotational and vibrational temperatures. During the increase in the vessel wall temperature by 350 K, with constant plasma parameters, rotational temperature of the excited BeD molecules increases by 500 K, whereas the vibrational temperature decreases by 400 K. Another experiment was the scan of the integrated edge density, during which electron density increases with the increasing edge density, and electron temperature decreases. During that scan for BeD, Trot decreases by 300 K and Tvib by 400 K over the change in an integrated edge density of ΔNe=+8×1018 m−2. Both trends were compared with the trends in other isotopes, and the qualitative results are similar, but the limited data available restrict the possibility of a full quantitative comparison. To simplify the comparison between the results presented here and other experiments or modeling data, and also to check the comparability of the pulses performed in different isotopes, the Be ion line ratios are used as benchmarks of the edge plasma condition.

Large eddy simulation of boundary layer combustion of hydrogen and hydrocarbon fuel films in a modeled scramjet combustor

Supersonic fuel film cooling is a promising way to simultaneously reduce the severe wall heat and friction load of the internal passage in a scramjet engine when operating at hypersonic conditions. Large eddy simulations were performed to investigate the cooling and wall friction characteristics of hydrogen and hydrocarbon films under inert and reactive circumstances. The results show that the essential difference of the turbulent state in the mixing layer contributes to the totally different behaviors of the cooling and wall friction reduction performances of the two fuel films. The turbulent transport processes between the hydrogen film and the mainstream are much weaker as compared to the case of hydrocarbon film, making inert hydrogen rather superior in cooling and friction reduction applications. Besides, the increase of wall temperature for hydrogen film under the inert case is mainly driven by the loss of hydrogen with high heat capacity instead of by direct heat addition. However, the film cooling performance severely deteriorates when the hydrogen film burns due to presence of severe heat release sources near the wall. On the other hand, combustion of hydrocarbon film in the boundary layer can remarkably improve its originally barely-satisfactory cooling and friction reduction performance to the level comparable to that of hydrogen film, due to the suppression of turbulent transport processes in the mixing layer and presence of heat absorption sources near the wall. Overall, the hydrogen film is more advantageous in friction reduction, while the hydrocarbon film is more suitable for cooling.

Electric field simulation in the electrochemical machining of a thin-walled part cavity

The article is aimed at simulating an electric field in the interelectrode gap during the electrochemical machining of a thin-walled part cavity for aerospace equipment. The study involved simulating the process of electrochemical cavity machining at a constant voltage in a steady-state mode in the COMSOL Multiphysics environment. The simulation was carried out for the scheme of electrochemical machining with a movable cathode and vertical and horizontal feeding to the workpiece surface undergoing machining while maintaining a constant interelectrode gap. The following simulation conditions were adopted: 12Cr18Ni10Ti stainless steel as the material of the cathode tube; AlMg6 aluminum alloy as the material of the thin-walled part; NaNO3 solution as the electrolyte. When simulating the electric field in the interelectrode gap, the heat exchange process was taken into account. The simulation of the electric field in the electrochemical cavity machining of a thin-walled part yielded a macro that allows the process simulation to be adapted to different input process conditions. As a result of the simulation, the following distribution patterns were obtained: current density in the cathode, potentials, electric field in the interelectrode gap and adjacent area, and process temperature of electrochemical machining. The simulation results show that the electric field lines are directed toward the cathode from the workpiece periphery. This means that anodic dissolution of material occurs in a given region, which characterizes the law concerning the distribution of potentials in an electrochemical cell. The temperature distribution pattern obtained in the simulation revealed that a temperature increase in the machining zone is insignificant. An increase in electrolyte temperature is shown to result in a proportional increase in wall temperature. Thus, the conducted study provides a theoretical insight into the examined process.

Combustion and emission performance evaluation in ammonia/hydrogen-powered system with baffle and secondary injection applied

Ammonia has recently gained significant attention due to its potential for zero carbon emissions during combustion, coupled with ease of storage and transportation. However, challenges related to poor combustion stability and high NOx emissions have limited the widespread use of NH3. To address these issues, this paper introduces a baffle structure and a secondary fuel injection strategy, and their optimal positions, widths, and injection ratios are determined through three-dimensional numerical calculations. The results demonstrate that the baffle effectively anchors the flame, enhancing both flame stability and wall temperature. Additionally, the disturbed flow near the baffle enhances the reaction between NO and NH3, resulting in reduced NO emission. The baffle structure with l = 1/10 and w = 4/5 achieves the optimal overall thermal characteristics, with approximately a 5.2 % increase in average wall temperature compared to the conventional straight-channel micro-planar combustor. Moreover, while increasing the secondary combustion injection ratio (R) significantly reduces NO emission, it also exacerbates ammonia leakage. The minimum achievable NO emission of 531 ppm is achieved at R = 0.1, where NH3 leakage is minimal. This study validates the feasibility of introducing a baffle and a secondary fuel injection strategy to enhance flame stability, improve thermal characteristics, and reduce NOx emissions in ammonia-hydrogen combustion.

Thermal performances and NOx emission studies on an ammonia-hydrogen fueled double-channel outlet micro-combustor for thermophotovoltaic applications

In this work, we propose and examine an ammonia-hydrogen fueled micro-combustor with a single-channel inlet and double-channel outlet (SIDO). The combustion characteristics and nitrogen oxide emission of ammonia/hydrogen-oxygen premixed combustion are explored. Comparison is then made between the conventional and the proposed SIDO combustors. It is found that our proposed new design could lead to an increase of the outer wall temperature and reduced nitrogen oxide emission. The performances of different hydrogen blended ratios (Φb), inlet velocities (Vin), and equivalence ratios (Φ) are evaluated. It is found that increasing Φb reduces the maximum flame temperature and the pressure loss, enabling the flame to move upstream. When Φb is set to 25 %, the convective heat transfer performance reaches its optimal level. The wall temperature and its uniformity can be improved by increasing Vin. However, it is accompanied by increased NO emissions at the outlet. Increasing Φ can significantly reduce nitrogen oxide emission, and such a reduction effect is much more remarkable at a lower Φb. Examining the exergy efficiency is shown to be greatly improved by increasing Φb. Increasing Φ could reduce the combustion efficiency of hydrogen in the mixed fuel and have almost no effect on ammonia. This study demonstrates the feasibility of improving thermal performance and reducing emissions by varying its structure for thermophotovoltaic applications.

Numerical Investigations of the Thermal-Hydraulic Characteristics of Microchannel Heat Sinks Inspired by Leaf Veins

A microchannel heat sink (MCHS) is a potential solution for chip and battery thermal management. The new microchannel structure is beneficial for further improving the thermal-hydraulic performance of MCHSs. Inspired by leaf veins, six new channel structures were designed, and the effects of the channel structures (three parallel structures named PAR I, II, and III and three pinnate structures named PIN I, II, and III), channel depths (0.4, 0.8, and 1.6 mm), and heat fluxes (20, 50, and 80 kW/m2) were investigated via numerical simulation. The cooling medium was water, and the heating area was 40 × 40 mm2. Both PAR II and PIN III exhibit superior overall performance, characterized by the highest Nusselt number and the lowest heating wall temperature. Moreover, PIN III demonstrates the lowest standard deviation in heating wall temperature, while PAR II exhibits the lowest friction factor. The greater the channel depth is, the larger the solid–liquid contact area is, leading to a reduced wall temperature at the interface under identical conditions of inlet Reynolds number and heating wall heat flux. Consequently, an increase in the Nusselt number corresponds to an increase in the friction factor. The maximum value and standard deviation of the heating wall temperature increase with increasing heat flux, while the Nusselt number and friction factor remain unaffected. The overheating near the two right angles of the outlet should be carefully considered for an MCHS with a single inlet–outlet configuration.

Effects of wall temperature and water vapor on the nitriding of stainless steel induced by ammonia flames

Ammonia is considered a promising alternative fuel for reducing CO2 emissions. However, the nitriding effect induced by ammonia flames poses a significant challenge that hinders its practical application in various industries. In the present study, to investigate the effects of temperature on the nitriding of stainless steel induced by ammonia flames, experiments were conducted by exposing SUS310S test plates to ammonia flames at different wall temperatures ranging from 550 °C to 850 °C. The distributions of chemical species in ammonia flames were obtained experimentally by means of the laser-induced fluorescence (LIF) technique and chemiluminescence measurement. Numerical simulations were also performed to estimate the ammonia flame structures with the consideration of surface reaction on the wall. In addition, the distributions of surface hardness and nitrogen atom concentration in the wall material were quantified by employing a nano-indenter and wavelength dispersive spectroscopy method (WDS), respectively. The LIF data for NH and NH3 concentration are in good agreement with the numerical results, highlighting the necessity of considering the surface reaction to accurately estimate the ammonia flame structure near the wall. It is also observed that both the surface hardness and the diffusion depth of nitrogen atoms into the wall decrease with increasing wall temperature, indicating a weakened nitriding effect at high wall temperatures. Notably, the NH3 concentration at the wall surface was identified as the most dominant parameter for the nitriding effect, while NH2 radicals also partially contribute to the nitriding. It is also found that the water vapor also hinders the nitriding.

A numerical study of the effects of jet-aft wall temperatures on the dynamics of jets in hypersonic crossflows

For high-speed vehicles such as scramjets, internal combustion chamber temperatures play an important role in the engine performance, with the influence of the temperature on the fuel injection dynamics being of key interest. In this study, large eddy simulations are employed to investigate a sonic jet in a Mach 5 crossflow with a momentum flux ratio of 5.8 and the parametrization of the temperature of the wall aft of the jet. Both uniform and non-uniform wall temperatures are analyzed, with two jet-to-crossflow temperature ratios of 8.06 and 3.23 investigated. It is found that the wall temperature primarily influences the near wall flow, with a small amount of entrainment into the jet plume via the counter-rotating vortex pair as the low velocity flow is limited by the near-wall shear layer. It is found that the aft-recirculation zone is expanded with the increasing wall temperature, which has the effect of increasing the penetration of the jet plume into the far field. Five recirculation regions are observed ahead of the jet, which are noted to result from the interaction between the crossflow and jet flow for both the adiabatic and temperature-controlled cases, with jet fluid flowing into the forward boundary layer, and thus near-wall mixing is observed. Horseshoe vortex strength is seen to dissipate when passing over the cooled walls, thus reducing the mixing potential near the wall, where the opposite is true for heated walls. Lateral spread of the horseshoe vortices is seen to increase with cooled walls, increasing the near-wall mixing potential.

Unsteady MHD Free Convection Flow of a Second Grade Casson Fluid with Ramped Wall Temperature

The present study delves into the analysis of unsteady free convection flow involving a non-Newtonian Casson fluid adjacent to an infinitely tall vertical plate. The primary objective of this article is to examine the flow behaviour of a second-grade Casson fluid under varying critical parameters. The plate exhibits a gradual increase in wall temperature and is situated within a porous medium. The governing equations are transformed into a dimensionless form, using non dimensionless variables. The method of Laplace transform (MOLT) is employed to derive accurate solutions for the temperature and velocity within the flow field. To enhance comprehension of the issue, The impact of different physical parameters on the flow field has been examined through the utilization of graphs and tables. Outcome of the problem was compared with existing one which was in good agreement. The study revealed that the velocity magnitude was lower in the scenario with ramped temperature compared to the scenario with isothermal temperature. Finally, skin friction and Nusselt numbers of the present work are tabulated. The significant outcome of the present work is that the flow field for the present phenomena is same as that of the existing one in absence of radiation parameter and heat source parameter when, u(0,t)=0, β=∞.

Experimental Study of Flow Boiling Regimes Occurring in a Microfluidic T-Junction.

Microchannel flow boiling is an efficient cooling method for high-heat-flux electronic devices. To understand the flow boiling regime in a T-shaped microchannel, this paper prepared T-shaped microchannels of different sizes and designed an experimental platform for the visualization of flow boiling in microchannels, and aimed to study the evolution characteristics of two-phase flow patterns in T-shaped microchannels. The influences of the flow rate and channel size on the boiling flow pattern inside a T-shaped microchannel were experimentally observed and quantitatively described. The results indicate that the occurrence position of the vaporization core gradually migrates from branch channel to main channel as the wall temperature increases. The flow boiling at the bifurcation of the T-shaped microchannel mainly includes the extrusion fracture flow, bubble flow, plug-annular alternating flow and annular flow, in which the annular flow can be further divided into the intermittent annular flow and the stable annular flow. In addition, a high flow rate and small channel size can lead to the disappearance of the bubble flow, and the presence of the bubble flow delays the appearance of the annular flow.

Spectra scaling of velocity components and pressure–strain correlations for hypersonic boundary layers at a range of wall-to-recovery temperatures

Flow similarity is one of the most desirable features for turbulence under different conditions. For hypersonic boundary layers, different wall temperatures are known to change the turbulence evolution by influencing the intercomponent energy transfer, while the flow similarity has received less attention. Based on direct numerical simulations, this work investigates the spectral distribution of velocity components and pressure–strain correlations for hypersonic boundary layers at Mach 6 and wall-to-recovery temperature ratios equal to 0.3, 0.5, 0.76, and 1. The wall-normal evolution of turbulent structures is compared by the spectra peak scale λSP, wall-normal location ySP, and the vertical profiles of peak scale λP. For all cases, the peak scale profiles exhibit linear increases with a height of 0.1≤y/δ≤0.25. The linear growth of the turbulence scale in the logarithmic region indicates the existence of self-similar structures, and the agreement of peak scales in the outer scaling suggests the flow similarity under different wall temperatures. Likewise, the streamwise pressure–strain term has the peak scale profile linearly dependent on the height for the same vertical range 0.1≤y/δ≤0.25 with velocity components, while the wall-normal and spanwise terms exhibit both linear and constant vertical dependence depending on the wall temperatures. With the increase in wall temperature, the peak scale exhibits broader constant vertical dependence and narrower linear vertical dependence. The cospectral analysis further confirms that the pressure–strain correlations are maximized at different spanwise-vertical aspect ratios of turbulence structures.