High Rotation Numbers Research Articles

ՈՒՂՂԱՁԻԳ ՊՏՏՄԱՆ ԱՌԱՆՑՔՈՎ ՀՈՂԱՄՇԱԿ ՖՐԵԶԻ ՈՒԺԱՅԻՆ ՎԵՐԼՈՒԾՈՒԹՅՈՒՆ

The article considers the issue of updating the machines designed for the cultivation of near-trunk and near-vine spaces. From the prospect of complete satisfaction of the agrotechnological and technical requirements of the mentioned machines, the rotary tillers with vertical rotation axis are preferable, which, however, need to get structurally developed. On this account, it is recommended to select planetary mechanism with external gear as a driving mechanism, which enables to ensure high rotation numbers of the tiller in case of relatively low rotation numbers of the rotor. The kinematic analysis of the driving mechanisms has been conducted, analytical expressions have been derived, which enable to determine the trajectory, speeds and accelerations of the tiller’s blades depending on the frequency of rotor’s rotation and the gear ratio of the mechanism. Based on the analytical expressions resulted from the kinematic research of the mechanism force analysis of the rotary tiller has been conducted. The estimated expressions of the general resistance moment value applied to the shaft of the moving rotor of the machine, as well as the value of resistance moments generated on the planet gear (satellite) rotors have been derived, which enable to identify the optimal kinematic and geometric parameters for the mechanism and rotary through the theoretical calculation method ensuring the optimal values of traction resistance force and other force factors in conditions of the stated working rules.

Heat transfer in a rotating impingement cooling channel with concave target surface

Jet impingement cooling is a common technique for cooling the leading edge of turbine blades that experience high thermal loads. This study examines the effect of rotation on jet impingement cooling by conducting experiments in a rotating channel with a concave target surface. The dimensionless parameters of the jet configuration are 3 for both jet-to-jet spacing and jet-to-target surface spacing. The jet rotation number and jet buoyancy number reach a maximum of 0.26 and 0.63, respectively. The jet Reynolds number ranges between 5,000 and 15,000. The results show that a large vortex is generated in the supply channel due to the Coriolis force, which changes the mass-flowrate distribution in each jet hole. Therefore, the heat transfer in both ends increases while that in the middle region decreases, resulting in a U-shaped heat transfer distribution in the radial direction. In addition, the rotational Coriolis force is the dominant factor that affects the rotating jet impingement cooling, while the buoyancy force can affect heat transfer at high rotation numbers. The rotation-to-stationary Nusselt number ratio is defined to separate the effects of the Reynolds number, thus, the heat transfer correlations are developed between Nusselt number ratio and rotation number.

Novel multi-stage vortex cooling with bypass for turbine blade leading edge design considering rotational effect

This work aims to comprehensively improve vortex cooling performance by suggesting a novel design in the blade leading edges of gas turbines. Under considering the effect of blade rotation, different multi-stage configurations with bypass are proposed. A series of validated calculations are performed based on solving steady-state Reynolds Averaged Navier-Stokes equations and the SST k-ω turbulence model. Heat transfer and flow characteristics of the different vortex cooling structures are analyzed at different rotational speeds. From the results, it can be concluded that: (1) under stationary conditions, compared to the single-stage model, the multi-stage design of vortex cooling can greatly enhance the heat transfer rate, and its average Nusselt number can be 87.6% higher, but the cost is the high total pressure loss. Nevertheless, the comprehensive thermal performance in the multi-stage configuration is still 7.2% higher at least. (2) When blade rotates, the heat transfer rates in all configurations generally decrease by the effect of the Coriolis force (at least 8.8% when rotational number is 0.072). With the increase of rotational speed, the unfavorable high friction loss in multi-stage design is also decreased. For example, the total pressure loss coefficient in multi-stage vortex cooling without bypass is decreased by 68.4% when Rotational number increases to 0.072. (3) The bypass design in the multi-stage model provides an effective way to control the heat transfer enhancement and total pressure loss. At a high rotational number of 0.072, using a bypass with a thickness of 0.25 mm, although the averaged Nusselt number drops by 9.9%, the decrease of total pressure loss reaches to 117%. This phenomenon implies that a proper multi-stage vortex cooling model with bypass design can significantly decrease the friction loss, at a negligible price of heat transfer reduction.

Maximum drag enhancement asymptote in spanwise-rotating viscoelastic plane Couette flow of dilute polymeric solutions

The existence of a maximum drag enhancement (MDE) asymptote at high rotation ( $Ro$ ) and Weissenberg ( $Wi$ ) numbers in turbulent viscoelastic spanwise-rotating plane Couette flow has been demonstrated. Specifically, it is shown that above a critical $Wi$ , drag enhancement plateaus and the MDE asymptote is realized in a broad range of $Ro$ . The mean velocity profiles at MDE appear to closely follow a log-law profile that has a nearly identical slope but different intercepts as a function of $Ro$ . Much like the maximum drag reduction (MDR) asymptote, the logarithmic function in MDE is closely followed if the mean velocity is plotted using the traditional inner variable scaling; however, the logarithmic function is not well defined when examined by the indicator function. Hence, in this study, we have used the logarithmic fit as a visual guide for the mean velocity profile. Last and perhaps the most intriguing finding of this study is that MDE occurs in the elasto-inertial turbulence (EIT) flow state; hence, it is mainly sustained by elastic forces much like the MDR flow state. To that end, a universal picture of elastically induced drag modification asymptotes is emerging, namely these asymptotic states are an inherent property of the elastically sustained EIT flow state.

ДИНАМИЧЕСКОЕ ИССЛЕДОВАНИЕ МЕХАНИЗМА ПЛАНЕТАРНОГО ПРИВОДА САДОВОЙ ПОЧВООБРАБАТЫВАЮЩЕЙ ФРЕЗЫ

The second article of the series considers the issues of inter-row and near-trunk land cultivation in orchards. As a result of the study and analysis of the literature, a classification and comparative evaluation of the existing machines intended for the cultivation of the mentioned areas was implemented. Both the advantages and disadvantages of rotary tillers with horizontal and vertical rotation axis were indicated. It has been stated that from the prospect of agro-technological and technical requirements of the mentioned machines, rotary tillers with vertical axis are preferable, which, anyhow, need to be upgraded. Based on the above stated, it has been recommended to select planetary mechanism with external gear as a transmission mechanism for the rotary tiller, which will enable to provide high rotation numbers for the disc of the tillers’ blade in case of relatively fewer rotation numbers of the rotor. It is theoretically justified and experimentally confirmed that from the point of view of effective tillage and a sharp decrease in the traction resistance of the unit, the optimal number of satellite cutters is three, located at an angle of 1200 to each other, and the number of knives is two, with a symmetrical arrangement. The expressions derived in the result of dynamic research on the recommended mechanism, enable to identify the optimal geometric parameters for the installation of the tillers’ disc knives, in case of which the resistance force factors of the cultivated medium, including the traction resistance force of the unit will assume the possible minimum values in conditions of the stated regime.

Heat transfer in a rotating lateral outflow trapezoidal channel with pin fins under high rotation numbers and Reynolds numbers

Existing heat transfer research on wedge-shaped channels with pin fins at the trailing edge has mainly focused on Reynolds numbers below 40,000. Larger inlet parameters are rarely considered, resulting in uncertainties in this aspect. Therefore, in this study, the heat transfer characteristics in a rotating lateral outflow trapezoidal channel with pin fins, which is a typical model of the internal cooling passage in a turbine blade, were experimentally investigated under the Reynolds number range of 10,000–110,000, rotation number range of 0–0.5, and speed range of 0–1000 rpm. The differences in the heat transfer at different entry conditions were compared. For the non-rotating condition, the heat transfer at a high Reynolds number (110,000) was four to nine times that at a low Reynolds number (10,000). For the rotating conditions, when the dimensionless parameter X/D (coordinate in radial direction/channel hydraulic diameter) was greater than seven for the inner surface and equal to eight for the outer surface, the heat transfer on the leading surface exceeded that of the trailing surface. Moreover, the critical rotation number, which varied with X/D, was noted on the leading surface. Finally, the heat transfer under a high Reynolds number and high speed were investigated. The findings under a high Reynolds number were similar to those under a low Reynolds number. The research of this paper supplements the heat transfer of wedge-shaped pin fins channel at the trailing edge of turbine blade under the condition of high Reynolds number and rotation number.

Numerical investigation into fluid-solid coupling characteristics of blade leading edge vortex cooling under different rotation numbers

In this paper, the fluid-solid coupling analysis is carried out on the vortex cooling. Under rotation conditions, the process of high-temperature gas scouring the blade and the vortex coolant cooling the blade is numerically calculated. At the same time, five rotation numbers of 0, 0.183, 0.339, 0.457 and 0.512 are selected. In addition, this paper proposes a method to improve vortex cooling performance under rotation conditions. The results show that at high rotation numbers, the centrifugal force drives coolant to flow downstream of vortex chamber. The downstream chamber accumulates a large amount of coolant to derive centrifugal buoyancy, which causes the back flow of coolant and makes the upstream heat transfer effect poor. As the rotation number increased from 0 to 0.512, the average Nusselt number on the target wall decreased by 35.49%. For the blade solid region, the effect of thermal load plays a major role on blade stress and displacement characteristics. Insufficient cooling performance in the chamber upstream leads to a higher temperature of the blade root, and a higher thermal stress concentration is generated because the blade root is constrained. In addition, by improving the intake chamber into a convergent structure, the coolant flow into the vortex chamber can be promoted, and the effect of back flow can be reduced, thereby obtaining a better vortex cooling performance. The target wall average Nusselt number of the convergent intake chamber structure is 977.17, which is 23.63% higher than that of the original rectangular intake chamber structure.

Effect of channel orientation on heat transfer in a rotating impingement cooling channel

The jet impingement cooling technology is usually applied in the turbine blade leading edge which suffers high thermal loads. In a high-speed rotating turbine blade, however, the channel orientation (β, the angle between the direction of the jet and the rotating plane) could alter the jets and heat transfer. Therefore, the effects of channel orientation (from 90∘ to 180∘) on heat transfer of confined jet impingement cooling are experimentally studied under an iso-thermal boundary. Both the jet-to-target surface distance and the jet-to-jet spacing are 3 times of the jet diameter. The jet Reynolds number varies from 5000 to 15,000, and the maximum jet rotation number reaches 0.24. The results show that the rotational effect on heat transfer is different in each channel orientation. In the cases of 90∘≤β≤ 135∘, a large vortex generated by the Coriolis force in the supply channel significantly changes the mass-flowrate distribution in each jet orifice. Hence, the heat transfer in the middle part decreases with the rotation number whereas the heat transfer at both ends increases, resulting in a “U-shape” pattern of heat transfer in the impingement channel. In the cases of 135∘<β≤ 180∘, however, the heat transfer throughout the stagnation zone decreases with the rotation number. The rotation-induced jet diversion is the primary factor that weakens the heat transfer, and jets are driven away from the target surface at high rotation numbers. Moreover, the heat transfer correlation on the stagnant zone is developed, which considers the effects of channel orientation and rotation number.

Heat Transfer in a Rotating Lateral Outflow Trapezoidal Channel with Pin Fins Under High Rotation Numbers and Reynolds Numbers

Heat Transfer in a Rotating Lateral Outflow Trapezoidal Channel with Pin Fins Under High Rotation Numbers and Reynolds Numbers

Thermal analysis of interaction between buoyancy induced flow under parallel rotation and rib induced vortices: Experimental and numerical study

This paper performing both experimental and numerical approaches underlines the aiding and opposing effects of secondary vortices resulting from parallel mode rotation on convective heat transfer coefficient in a rectangular channel in smooth and rib roughened channels. The Nusselt number is obtained by measuring the wall and fluid temperature at the Reynolds number ranging from 5118 to 10,677 and 0.07<Δρ/ρ<0.42. In addition, the Nusselt number is investigated in ribbed channels with one wall being perpendicularly ribbed at pitch ratio (P/e) and blockage ratio (e/Dh) equal to 15 and 0.088, respectively. Numerical simulations also allow to consider the effects of rotational induced secondary flows caused by centrifugal and the Coriolis forces in high rotation numbers (0<Ro<0.56) and Buoyancy numbers (0<Buo<1). The numerical results with non Boussinesq approximation for density variation show good agreement with experimental results, while it is revealed that the Nusselt number is underestimated if Boussinesq approximation is used. As the Reynolds number increases, the larger Buoyancy number is required to affect the Nusselt number. That is, under certain conditions which is expressed in terms of GrΩα/Re the rotational buoyancy effects may be negligible and the Nusselt number is equal to stationary case. However, in rib roughened channels the rotational buoyancy causes the reattachment point to occur closer to upstream rib while physical presence of ribs reduce the enhancing effects of rotation. Thus, for practical use in rotating cooling systems such as turbo-generators or electrical machinery, rib roughened channels are not recommended.

Heat transfer in an impingement cooling channel under isothermal boundaries at high rotation numbers

The jet impingement cooling technology is usually applied in the turbine blade leading edge which suffers the highest heat flux and needs priority protection. Therefore, heat transfer performances in a rotating impingement cooling channel under an isothermal boundary are experimentally studied. Both the jet-to-target surface spacing and the jet-to-jet spacing are 3 times the jet hole diameter. The effects of Coriolis force and buoyancy force on heat transfer are focused. And the maximum rotation number and buoyancy number reaches 1.63 and 8.06, respectively. The Reynolds number varies from 7119 to 21,358. Besides, numerical simulations are conducted to predict the flow field. The results show that the heat transfer in the impingement channel is determined by the radial mass-flowrate distribution of supply channel in both static and rotating states. Moreover, the rotation enhances the heat transfer at both ends but decreases the heat transfer in the middle-radius due to the stagnant zone induced by Coriolis force in the supply channel, resulting in large thermal stress on the target surface. However, the heat transfer is insensitive to the rotational effects when the rotation number exceeds 0.42. There is a critical rotation number for each location, before which the effect of buoyancy force could be neglected. Once the rotation number is greater than this value, the effect of buoyancy force increases with the wall-to-fluid temperature ratio.

Heat transfer characteristics in a rotating AR=4:1 channel with different channel orientations at high rotation numbers

In order to reveal the effect of channel orientations on rotational heat transfer performance, this paper presents an experimental model of AR = 4:1 smooth rectangular channel. The stationary and rotational heat transfer characteristics of the channel are studied in the range of Re = 10,000–40,000 and Ro = 0–1.23 under the channel orientation of 90° and 135°, which represent the basic one and realistic one, respectively. The experimental results indicate that for the trailing wall, the 90° channel shows a typical large range enhancement of rotational heat transfer, while the rotational effect becomes negative in most areas at 135° case. As the rotation number exceeds 0.7, the heat transfer of the trailing surface is greatly improved by rotational effect in 90° channel. When the channel was orientated at 135°, the leading surface heat transfer is more sensitive to rotation under the low rotation number (Ro < 0.3), and 20%–30% worse than non-rotating cases. The averaged Nusselt ratios correlations under the channel orientation of 90° and 135° have been developed for further engineering applications.

Line-strengths, collisional coefficients and narrowing parameters in the ν3 band of methane: H2, He, N2, O2, Ar and CO2 collider effects

The ν3 fundamental absorption band of methane (12CH4) dominates the 3.3–3.4 μm infrared spectral window and has been extensively used for atmospheric, planetary and astrophysical investigations. Spectroscopic data, such as line positions, line-strengths and foreign-collisional coefficients, are needed to analyze the infrared spectra of planetary atmospheres for the understanding of relevant physical chemistry. In this study, high-resolution infrared spectra of 12CH4 belonging to the ν3 fundamental vibrational band are recorded over 2884–2969 cm−1 with a difference–frequency–generation (DFG) laser having a linewidth of Δν ≈ 0.0002 cm−1. Line-strengths as well as H2-, He-, N2-, O2-, Ar- and CO2- broadening coefficients are determined for 49 methane transitions at room temperature. Data are retrieved using Voigt and Galatry profiles to compute the measured line shape of each individual transition at various pressures. Narrowing coefficients due to Dicke effect are also determined. The new data extend and supplement previous measurements over the target spectral region (2884–2969 cm−1) where very fewer studies are reported. In particular, the present work is the first known complete determination of broadening data and narrowing parameters at high rotational quantum numbers of the P-branch of the ν3-CH4 band.

The new nitrogen dioxide (NO2) linelist in the GEISA database and first identification of the ν1+2ν3-ν3 band of 14N16O2

We have generated new lists of line position, line intensity and line shape parameters of nitrogen dioxide (14N16O2 and 15N16O2), here labeled as “GEISA-19”, which have been included in the (Gestion et Etude des Informations Spectroscopiques Atmosphériques) GEISA database (https://geisa.aeris-data.fr/). Except for the far infrared and the 13.3 µm regions, all spectral regions of the 1153–4775 cm−1 spectral domain are significantly modified by this major update of the GEISA linelist. For the 6.2 µm and 3.4 µm spectral regions, which correspond to the strongest absorption of NO2, we proceed to a complete replacement of the lists for the first hot bands, ν2 + ν3-ν2 and ν1 +ν2 + ν3-ν2, respectively, and to the inclusion, whenever possible, of higher order hot bands involving the (1,0,0), (0,2,0) and (0,0,1), (1,1,0), (2,0,0) or (0,0,2) states as lower states. Also, the ν1 + ν3 linelist was improved for high rotational quantum numbers and the ν3 and ν1+ν3 bands for 15N16O2, which is the second most abundant isotopologue of NO2, are now included in the database. Finally several weak cold bands in the 2.2–4.9 µm region were added for the first time to the GEISA linelist. These new vibration rotation transitions were generated using existing literature data or making use of experimental data extracted from high resolution Fourier transform spectra recorded at SOLEIL for the purpose of this study. One outcome of this study was the first identification of the ν1+2ν3-ν3 hot band, leading to the first determination of the (1,0,2) energy level parameters. Also, an improved set of parameters was derived for the (0,1,1) state. The validation of the GEISA-19 linelist was performed through a detailed comparison at 296 K between computed and observed Fourier transform laboratory spectra. Also, the consistency, from one band to another, of the energy levels values was carefully checked. Finally inter-comparisons and verifications were performed using the recent versions of the HITRAN (https://hitran.org/) and HITEMP databases [R.J. Hargreaves, I. E. Gordon, L. S. Rothman, S. A. Tashkun, V. I. Perevalov, A. A. Lukashevskaya, S. N. Yurchenko, J. Tennyson, and H. S.P. Müller. J. Quant. Spectrosc. Radiat. Transf. 232 35 (2019)]. Our conclusions are that, at 296 K, GEISA-19 is of better quality than HITRAN2016-updated or HITEMP in the overall 1153–4775 cm−1 spectral region. As compared to its previous version, this new linelist will lead to an improved quality of the NO2 retrievals that will be performed for the future IASI-NG (Infrared Atmospheric Sounding Interferometer New Generation) satellite instrument (https://iasi-ng.cnes.fr/fr). However, contrary to HITEMP, GEISA-19 which does not include transitions involving high rotational quantum numbers or belonging to very high order hot bands cannot be used for hot temperature conditions.

Hot-wire experimental investigation on turbulent Prandtl number in a rotating non-isothermal turbulent boundary layer

This experiment used a parallel array of hot wire probes to simultaneously measure the temperature and velocity fields in the non-isothermal turbulent boundary layer of a rotating straight channel. The Reynolds numbers are 15,000 and 25,000, respectively. The rotation numbers are 0, 0.07, 0.14, 0.21 and 0.28, respectively. The purpose of this study is to calculate the turbulent Prandtl number in a rotating non-isothermal turbulent boundary layer. Due to the difficulty in measuring local turbulent Prandtl numbers, this study focuses on the average turbulent Prandtl numbers in the logarithmic region instead. Under static conditions, this value is taken as 0.9 normally. This research finds that rotation conditions can affect the turbulent Prandtl number by affecting the properties of velocity and temperature boundary layers. The change range of the turbulent Prandtl number is roughly 0.6–1.1. The influence of the leading side is greater than that of the trailing side, especially at high rotation numbers. This can provide validation and guidance for numerical simulation. Other information within the turbulent boundary layer is also discussed. It is hoped that this study would enhance our understanding of the mechanism of turbulent flow in the turbulent layer at rotating conditions.

Computational Analysis of Rotating Effects on Heat Transfer and Pressure Loss of Turbulent Flow in Detached Pin Fin Arrays With Various Clearances

Abstract A detailed computational analysis is carried out on the heat transfer and pressure loss of a turbulent flow in detached pin fin arrays with various clearance values for the Reynolds number range of 20,000–80,000 and the rotation number range of 0–0.3. Clearances exist at the midheight of the detached pin fins, which account for 10%, 15%, and 20% of the full pin fin's height, respectively. The clearances release the fluid stagnation and reduce the bulk flow turbulent mixing level, which significantly reduces the pressure loss. Compared with the pin fin arrays, the pressure loss is decreased by up to 30.5% with the increase of the clearance value for the detached pin fin arrays. Also, the detached pin fin arrays show a maximum increase in the total Nusselt numbers by about 13.5%. Furthermore, the rotation effects can increase the friction factors as well as the Nusselt numbers simultaneously in both the pin fin arrays and the detached pin fin arrays. A higher rotation number can promote the heat transfer enhancement and uniformity in the detached pin fin channels.

Effects of Aspect Ratio on Heat Transfer and Pressure Drop in Stationary and Rotating Two-Pass Rectangular Channels with Smooth Wall

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The Ritz program for assigning rotational and rovibrational transitions in asymmetric-top molecules

The Ritz program is a user-interactive software package that simulates and enables the assignment of spectra of asymmetric top molecules, up to high rotational quantum numbers. The set of initial assignments can be extended using generated predictions for line positions. The graphical interface of the program handles wide spectral features corresponding to overlapped lines by fitting the expected number of profiles to the experimental contour. Features of the program allow for the detection and examination of Coriolis interactions. Initially designed to work for methanol and its isotopologues, the program has been modified to assign the spectra of cyanamide, hydrazine, acetaldehyde, and oxetane. An extension of the program, LaseRitz, has been developed for the assignment and prediction of optically pumped far-infrared laser transitions. Our paper presents a description of how the Ritz program works and provides an overview of studies carried-out using this software.

Effect of Blockage Ratio on Heat Transfer and Pressure Drop in Rotating Ribbed Channels at High Rotation Numbers

At high rotation numbers, the rotational effects on heat transfer and flow could be diverse among the channels with different blockage ratios. However, most studies are conducted under low rotation number (less than 0.25) and selected blockage ratio. This paper experimentally investigates the effect of rib blockage ratio (ranges from 0 to 0.3) on pressure loss and heat transfer in a rotating square channel under high rotation number (up to 0.81). The ribs staggered on leading and trailing walls were oriented 90° to the mainstream flow. The Reynolds number and the wall-to-fluid temperature ratio varied from 20 000 to 40 000 and 0.08 to 0.2, respectively. The results showed that a larger blockage ratio resulted in a better heat transfer but a higher pressure drop. The optimum blockage ratio was 0.1 for the best thermal performance. The rotational effects were weakened in the passage with a higher blockage ratio, where the critical rotation number could not be observed. Moreover, the heat transfer enhancement induced by rotation was more significant when the temperature ratio increased. Finally, the correlations were developed for the pressure drop and the convective heat transfer on the leading and trailing edges.

Effects of rotation number on heat transfer and fluid flow in a three-pass serpentine passage with lateral outflow

The purpose of this study is to experimentally and numerically investigate the effects of rotation number on heat transfer and fluid flow in a three-pass serpentine passage with lateral outflow. In the present study, the rotation number varies from 0 to 0.09, and the inlet Reynolds number is 5000. The heat transfer coefficient distribution of the three-pass serpentine passage is measured using the transient liquid crystal technique. The current work fills the research gap of the effect of rotation number on heat transfer distribution in a three-pass serpentine passages with lateral outflow. The results of this study show that the span-wise-averaged Nusselt numbers in the region of l/d 33.6 increase monotonically with the rotation number increasing, particularly in l/d = 6.4, with a maximum increase of 58.5%. However, the rotation reduces the Nusselt numbers of the middle passage by between 2.6 and 7.3% when the rotation number increases from 0 to 0.06. The area-averaged Nusselt numbers rapidly decrease in the area of Ai = 4; this phenomenon is more obvious at higher rotation numbers, and the maximum decrease is 34.6%. The pressure coefficient in the region of l/d < 14 tends to increase gradually along the flow direction when Ro = 0.09. The rotation changes the flow direction and shrinks the vortex size in the lateral-outflow passage. Accordingly, the pressure coefficient rapidly increases by 74.1% in the lateral-outflow passage when Ro = 0.06 and Ro = 0.09.