High Rotation Numbers Research Articles

Unsteady RANS simulation of turbulent flow and heat transfer in ribbed coolant passages of different aspect ratios

The flow and heat transfer in ribbed coolant passages of aspect ratios (AR) 1:1, 4:1, and 1:4 are numerically studied through the solution of the unsteady Reynolds averaged Navier–Stokes (URANS) equations. The URANS procedure, which utilizes a two equation k– ε model for the turbulent stresses, is shown to resolve large-scale bulk unsteadiness. The computations are carried out for a fixed Reynolds number of 25,000 and density ratio of 0.13, while the Rotation number is varied between 0.12 and 0.50. At higher rotation numbers (⩾0.5) at least three inter-rib modules are required to ensure periodicity in the streamwise direction. The flow exhibits unsteadiness in the Coriolis-driven secondary flow and in the separated shear layer. The average duct heat transfer is the highest for the 4:1 AR case. For this case, the secondary flow structures consist of multiple roll cells that direct flow both to the trailing and leading surfaces. The 1:4 AR duct shows flow reversal along the leading surface at high rotation numbers. For this AR, the potential for conduction-limited heat transfer along the leading surface is identified. The friction factor reveals an increase with the rotation number, and shows a significant increase at higher rotation numbers (∼ Ro = 0.5).

곡관부를 가지는 내부 냉각유로에서 회전수 변화에 따른 열전달 및 유동 특성 (II) - 평행한 요철배열 덕트 -

The present study investigates heat/mass transfer and flow characteristics in a ribbed rotating passage with turning region. The duct has an aspect ratio (W/H) of 0.5 and a hydraulic diameter () of 26.67 mm. Rib turbulators are attached in the cross arrangement on the leading and trailing surfaces of the passage. The ribs have a rectangular cross section of and an attack angle of . The pitch-to-rib height ratio (p/e) is 7.5, and the rib height-to-hydraulic diameter ratio () is 0.075. The rotation number ranges from 0.0 to 0.20 while the Reynolds number is constant at 10,000. To verify the heat/mass transfer augmentation, internal flow structures are calculated for the same conditions using a commercial code FLUENT 6.1. The heat transfer data of the smooth duct for various Ro numbers agree well with not only the McAdams correlation but also the previous studies. The cross-rib turbulators significantly enhance heat/mass transfer in the passage by disturbing the main flow near the surfaces and generating one asymmetric cell of secondary flow skewing along the ribs. Because the secondary flow is induced in the first-pass and turning region, heat/mass transfer discrepancy is observed in the second-pass even for the stationary case. When the passage rotates, heat/mass transfer and flow phenomena change. Especially, the effect of rotation is more dominant than the effect of the ribs at the higher rotation number in the upstream of the second-pass.

Transport properties of H–N2 mixtures

Transport coefficients (shear viscosity, volume viscosity, thermal conductivity, and mass and thermal diffusion coefficients) of H–N2 mixtures in the dilute-gas limit have been calculated from the intermolecular potential in the temperature range 300–2000K using the classical trajectory method. The intermediate results pertaining to H–N2 binary interactions are reported, mainly in terms of cross-section ratios. Cross-sections evaluated with the Mason–Monchick approximation yield very good results for this system, the largest deviations, about 2.5%, being observed for the thermal diffusion coefficient. The accuracy here of this approximation can primarily be attributed to a light H atom and a weakly non-spherical potential resulting in a high rotational collision number. Furthermore, we investigate to which H–N2 cross-sections and their ratios the values of the mixture transport coefficients are most sensitive. Our results indicate that, for some cross-section ratios, reliance on universal correlations at high temperatures, often used in flame codes, can induce sizeable errors in the thermal conductivity coefficient and especially in the thermal diffusion coefficients. We also observed that the volume viscosity is particularly sensitive to the value of the cross-section for internal energy relaxation in H–N2 collisions.

곡관부를 가지는 내부 냉각유로에서 회전수 변화에 따른 열전달 및 유동 특성 ( I ) - 엇갈린 요철배열 덕트 -

The present study investigates heat/mass transfer and flow characteristics in a ribbed rotating passage with turning region. The duct has an aspect ratio (W/H) of 0.5 and a hydraulic diameter () of 26.67 mm. Rib turbulators are attached in the cross arrangement on the leading and trailing surfaces of the passage. The ribs have a rectangular cross section of and an attack angle of . The pitch-to-rib height ratio (p/e) is 7.5, and the rib height-to-hydraulic diameter ratio () is 0.075. The rotation number ranges from 0.0 to 0.20 while the Reynolds number is constant at 10,000. To verify the heat/mass transfer augmentation, internal flow structures are calculated for the same conditions using a commercial code FLUENT 6.1. The heat transfer data of the smooth duct for various Ro numbers agree well with not only the McAdams correlation but also the previous studies. The cross-rib turbulators significantly enhance heat/mass transfer in the passage by disturbing the main flow near the surfaces and generating one asymmetric cell of secondary flow skewing along the ribs. Because the secondary flow is induced in the first-pass and turning region, heat/mass transfer discrepancy is observed in the second-pass even for the stationary case. When the passage rotates, heat/mass transfer and flow phenomena change. Especially, the effect of rotation is more dominant than the effect of the ribs at the higher rotation number in the upstream of the second-pass.

Fluid Flow and Heat Transfer in Rotating Curved Duct at High Rotation and Density Ratios

Prediction of flow field and heat transfer of high rotation numbers and density ratio flow in a square internal cooling channels of turbine blades with U-turn as tested by Wagner et al. (ASME J. Turbomach., 113, pp. 42–51, 1991) is the main focus of this study. Rotation, buoyancy, and strong curvature affect the flow within these channels. Due to the fact that RSM turbulence model can respond to the effects of rotation, streamline curvature and anisotropy without the need for explicit modeling, it is employed for this study as it showed improved prediction compared to isotropic two-equation models. The near wall region was modeled using enhanced wall treatment approach. The Reynolds Stress Model (RSM) was validated against available experimental data (which are primarily at low rotation and buoyancy numbers). The model was then used for cases with high rotation numbers (as much as 1.29) and high-density ratios (up to 0.4). Particular attention is given to how secondary flow, velocity and temperature profiles, turbulence intensity, and Nusselt number area affected by Coriolis and buoyancy/centrifugal forces caused by high levels of rotation and buoyancy in the immediate vicinity of the bend. The results showed that four-side-average Nu, similar to low Ro cases, increases linearly by increasing rotation number and, unlike low Ro cases, decreases slightly by increasing density ratio.

High-resolution infrared and microwave study of 10BF2 OH and 11BF2OH: the 5, 6l, 71, 8l, 91 and 81 91 vibrationally excited states

High-resolution (≤2.4×10−3cm−1) Fourier transform infrared spectra of gas-phase 10B-enriched isotopic and natural samples of BF2OH (difluoroboric acid) were recorded in the 400–4000 cm−1 spectral range. Starting from the results of a previous study [Collet, D., Perrin, A., Burger, H., and Flaud, J.-M., 2002, J. Molec. Spectrosc. 212, 118], which involved the v 8 10BF2 out-of-plane bending) and v9 (OH torsion) bands of 11BF2OH, it has been possible to perform the first rovibrational analysis of the v 5 10BF2 bending), v 8 , v 9 and v 8+v 9 bands of’11BF2OH, and of the v 7 (F2BO in-plane bending), v 5, and v 8+v9 bands of 11BF2OH up to very high rotational quantum numbers. In addition, microwave transitions within the 51, 61, 71 and 81 vibrational states of 11BF2OH were measured using predictions from ab initio calculations [Breidung, J., Demaison, J., D'Eu, J.-F., Margules, L., Collet, D., Mkadmi, E. B., Perrtn, A., And Thiel, W., 2004, J. Mol. S ectrosc. (in press)]. The v 5, v 8, v 9 and v 8+v 9 bands of’ bands of 10BF2OH and the v 8+v 9 band of'BF2OH are not significantly affected by ptrturbations, and the experimental 51, 81 and 91 of 10BF2OH and the 8191 energy levels of BF20H and 10BF2OH could be reproduced using a simple Watson-type Hamiltonian. For the v 5 and v 7 bands of 11BF2OH, C-type Coriolis interactions coupling the 51 and 71 energy levels with those of the 72 and 61 dark states, respectively, were accounted for in the calculation. In addition, an updated set of rotational parameters was provided for the unperturbed 81 and 91 vibrational states of 11BF2OH using the data from our previous analysis. In all these cases, the upper state parameters derived in this work enabled the reproduction of both the infrared and microwave data to within experimental uncertainties.

Quantum and classical studies of the O(3P) + H2(v = 0-3,j = 0) --> OH + H reaction using benchmark potential surfaces.

We present results of time-dependent quantum mechanics (TDQM) and quasiclassical trajectory (QCT) studies of the excitation function for O(3P) + H2(v = 0-3,j = 0) --> OH + H from threshold to 30 kcal/mol collision energy using benchmark potential energy surfaces [Rogers et al., J. Phys. Chem. A 104, 2308 (2000)]. For H2(v = 0) there is excellent agreement between quantum and classical results. The TDQM results show that the reactive threshold drops from 10 kcal/mol for v = 0 to 6 for v = 1, 5 for v = 2 and 4 for v = 3, suggesting a much slower increase in rate constant with vibrational excitation above v = 1 than below. For H2(v > 0), the classical results are larger than the quantum results by a factor approximately 2 near threshold, but the agreement monotonically improves until they are within approximately 10% near 30 kcal/mol collision energy. We believe these differences arise from stronger vibrational adiabaticity in the quantum dynamics, an effect examined before for this system at lower energies. We have also computed QCT OH(v',j') state-resolved cross sections and angular distributions. The QCT state-resolved OH(v') cross sections peak at the same vibrational quantum number as the H2 reagent. The OH rotational distributions are also quite hot and tend to cluster around high rotational quantum numbers. However, the dynamics seem to dictate a cutoff in the energy going into OH rotation indicating an angular momentum constraint. The state-resolved OH distributions were fit to probability functions based on conventional information theory extended to include an energy gap law for product vibrations.

Mass-Transfer Distribution in Rotating, Two-Pass, Ribbed Channels with Vortex Generators

Local and global effects of cylindrical vortex generators on the mass-transfer distributions over the four active walls of a square, rib-roughened rotating duct with a sharp 180-deg bend are investigated. Cylindrical vortex generators (rods) are placed above, and parallel to, every other rib on the leading and trailing walls of the duct so that their wake can interact with the shear layer and recirculation region formed behind the ribs, as well as the rotation-generated secondary e ows. Local increases in near-wall turbulence intensity resulting from these interactions give rise to local enhancement of mass (heat)transfer. Measurements are presented for duct Reynolds numbersReintherange5 £ 10 3‐3 £ 10 4 andforrotationnumbersin therange0 ‐0.3. Therib height-to-hydraulic diameter ratio e/Dh is e xed at 0.1, and the rib pitch-to-rib height ratio P/e is 10.5. The vortex generator rods have a diameter-to-rib height ratio d/e of 0.78, and the distance separating them from the ribs relative to the rib height s/e is 0.55. Mass-transfer measurements of naphthalene sublimation have been carried out using an automated acquisition system and are correlated with heat transfer using the heat/mass transfer analogy. The results indicate that the vortex generators tend to enhance overall mass transfer in the duct, compared to the case where only ribs are present, both before and after the bend at high Reynolds and rotation numbers. Local enhancements of up to 30%are observed on all fourwalls oftheduct. At low Reynolds numbers, forexample, 5 ££ 10 3 , the insertion of the rods often leads to mass-transfer degradation. At high Reynolds numbers, for example, 3 ££ 10 4 , the enhancement due to the rods occurs on the surfaces stabilized by rotation (trailing edge on the inlet pass and leading edge on the outlet pass )and the side walls. The enhancement is more pronounced as the rotation number is increased. The detailed measurements in a ribbed duct with vortex-generator rods clearly show localized regions of enhanced mass (heat) transfer at Reynolds and rotation numbers within the envelope of practical interest for gas-turbine blade cooling applications.

Fingering Instability and Maximum Radius at High Rotational Bond Number

The spin-coating in the modern microfabrication practice takes place at a high rotational Bond number, Bo. An experimental study of fingering instability and maximum attainable radius at high Bo for both the injected liquid and released drop is presented. Compared to the released drop procedure, the effect of liquid injection tends to decrease the critical radius and the number of fingers at high Bo, although this effect is negligible for low Bo. The characteristics of apparent contact angles of the liquid front and the critical capillary number for high Bo are quite different from those for low Bo. This difference mainly comes from the competition between the speed of liquid spreading pushed by the centrifugal force and the speed of molecular wetting. For the number of fingers, are constant and independent of Bo. For high increases rapidly with Bo. The maximum attainable radius is almost independent of the fluid’s viscosity μ and injection Reynolds number but is only a function of Bo for the fluids of high viscosity considered in this work. © 2001 The Electrochemical Society. All rights reserved.

Heat Transfer of Compressed Air Flow in a Spanwise Rotating Four-Pass Serpentine Channel

Convective heat transfer of compressed air flow in a radially rotating four-pass serpentine channel is investigated experimentally in the present study. The coolant air was compressed at 5 atmospheric pressure to achieve a high rotation number and Reynolds number simultaneously. The main governing parameters are the Prandtl number, the Reynolds number for forced convection, and the rotation number for the Coriolis-force-induced cross-stream secondary flow and the Grashof number for centrifugal buoyancy. To simulate the operating conditions of a real gas turbine, the present study kept the parameters in the test rig approximately the same as those in a real engine. The air in the present serpentine channel was pressurized to increase the air density for making up the low rotational speed in the experiment. The air flow was also cooled to increase the density ratio before entering the rotating ducts. Consequently, the order of magnitude of Grashof number in the present study was the same as that in real operating conditions. The local heat transfer rate on the walls of the four-pass serpentine channel are correlated and compared with that in the existing literature.

Experimental and theoretical study of line mixing in methane spectra. I. The N2-broadened ν3 band at room temperature

Line-mixing effects have been studied in the ν3 band of CH4 perturbed by N2 at room temperature. New measurements have been made and a model is proposed which is not, for the first time, strictly empirical. Three different experimental set ups have been used in order to measure absorption in the 2800–3200 cm−1 spectral region for total pressures in the 0.25–2 and 25–80 atm ranges. Analysis of the spectra demonstrates the significant influence of line mixing on the shape of the Q branch and of the P and R manifolds. A model is proposed which is based on state-to-state collisional transfer rates calculated from the intermolecular potential surface with a semiclassical approach. The line-coupling relaxation matrix is constructed from these data and two additional parameters which are fitted on measured absorption. Comparisons between measurements and spectra computed accounting for and neglecting line mixing are made. They prove the quality of the approach which satisfactory accounts for the effects of pressure and of rotational quantum numbers on the spectral shape under conditions where modifications introduced by line mixing are important. For high rotational quantum number lines, the main features induced by collisions are predicted but some discrepancies remain; the latter may be due to improper line-coupling elements but there is strong evidence that the use of inaccurate line broadening parameters also contributes to errors in calculated spectra.

Absolute HCO concentration measurements in methane/air flame using intracavity laser spectroscopy

Intracavity laser absorption spectroscopy was used to measure the absorption spectra of a premixed, flat methane/air flame at a total pressure of 30 Torr. The spectra were measured in the spectral range of 16 000–16 300 cm−1. A flat flame burner was placed inside the cavity of a broadband dye laser pumped by a cw argon-ion laser. The spectrum of the laser output was measured by a high resolution spectrograph (with a spectral resolution of 0.003 nm). The spectrum of HCO radicals (Ã 2A′′←X̃ 2A transition) was measured with a high signal-to-noise ratio at different positions above the burner, providing the first quantitative measurement of the absolute concentrations of the HCO radical in flames. The linewidths of the individual rotational lines in the spectrum can be closely fitted by the equation Γ=X+ZN2(N+1)2, where X=0.37±0.03 cm−1 and Z=(8±0.5)10−6. The rotational temperature of the HCO radicals was evaluated from the spectra, but the error and the data scatter are relatively high since the lines with a high rotational quantum number N are strongly superimposed with lines from different branches. The “hot band,” which can be assigned to the transition (0,0,1)–(0,9,1), was observed in spectra measured at high temperature. The value ν3″=1859 cm−1 is evaluated from the position of this “hot band.” The concentration profile of the HCO radical has a maximum value of about 1.2×1013 molecules/cm3 which is in reasonable agreement with computer simulation results, when the uncertainties of the absorption cross section and of the rate constants for HCO reactions are taken into account. The relatively strong lines of the CH2 radical spectrum (the b̃ 1B1←ã 1A1 transition) were also recorded in the studied wavelength range. The spectra of these two radicals can be measured simultaneously which is advantageous in combustion diagnostics.

Collisional removal of CD(A 2Δ, B 2Σ − and C 2Σ +) by deuterated ketene

The collisional removal of CD(A 2Δ, B 2Σ − and C 2Σ +) by deuterated ketene has been studied. For several rotational levels of υ=0 of the A 2Δ state, rate constants between 2.3 × 10 −10 and 3.6 × 10 −10 cm 3 molecule −1 s −1 are measured; the rate constants show a slightly increasing tendency towards levels with high rotational quantum number. The removal rate obtained for the unresolved rotational levels of A 2Δ, υ′ = 2 is similar to that measured for the high rotational levels of υ′ = 0. The total removal rate constants measured for the B 2Σ − and C 2Σ + states are 3.6 × 10 −10 and 4.8 × 10 −10 cm 3 molecule −1 s −1 respectively. For the B 2Σ − state the rate constant shows no dependence on vibrational quantum number.

Thermodynamical nonequilibrium nitrogen plasmas in a direct-current arcjet engine nozzle

Spectroscopic measurements were carried out to understand the arc structure and the flowfield in a 10-kW-class water-cooled direct-current nitrogen arcjet engine with a supersonic expansion nozzle for material processing. In the expansion nozzle, the pressure and electron density drastically decreased downstream, and therefore the plasma was in thermodynamical nonequilibrium, although the plasma in the constrictor was expected to be nearly in a temperature-equilibrium condition. The radial profiles of the physical properties for N/sub 2/ and N/sub 2//sup /showed that there existed a core flow with high vibrational and rotational temperatures and large electron number densities on the center axis, even at the nozzle exit. Both of these temperatures on the arcjet axis at the nozzle exit and the electron temperature in the constrictor increased linearly with the input power, regardless of mass flow rate. The vibrational temperature ranged from 6000 to 10000 K in input power levels of 5-11 kW and the rotational temperature from 500 to 2000 K.

A New Analysis of the OH Radical Spectrum from Solar Infrared Observations

The solar spectrum offered the opportunity to discover OH lines with high rotational quantum numbers, which do not appear on laboratory spectra. On solar absorption spectra, we have identified about 580 lines, among which about 400 were observed for the first time. They belong to pure rotational transitions in the ground state (v= 0 → 3;[formula]= 48.5), as well as to the (1–0), (2–1), and (3–2) vibration–rotation bands[formula]= 32.5). Previous pure rotation, vibration–rotation, and Λ-doubling data sets related to thev= 0 up to 3 levels were fitted simultaneously together with this new set of data, in order to obtain a very complete and accurate set of molecular constants for theX2Π ground state.

Pure Rotational Spectra of HNCO in the Far Infrared: Ground State Analysis

The pure rotational spectrum of the quasilinear molecule HNCO and some of its isotopomers was measured with the Giessen high-resolution Fourier transform spectrometer in the far infrared. In addition to a-type transitions with high rotational quantum number, b-type transitions from Ka = 1 ← 0 to Ka = 8 ← 7 for HNCO and DNCO, and from Ka = 1 ← 0 to Ka = 5 ← 4 for HN13CO were identified. Several rotational transitions near 600 GHz were also measured using the Cologne submillimeter-wave spectrometer with a high-frequency backward wave oscillator as source. Rotational parameters were determined using both Watson′s S-reduced asymmetric rotor Hamiltonian and for comparison a linear molecule Hamiltonian. The centrifugal distortion resonance between the ground state and the lowest excited bending vibration was clearly observed and analyzed by a second-order perturbation treatment. The observed K dependence of the rotational parameter B(K) is caused by the combined effects of centrifugal distortion resonance and quasilinearity.

Developing Buoyancy-Modified Turbulent Flow in Ducts Rotating in Orthogonal Mode

A numerical study of developing flow through a heated duct of square cross section rotating in orthogonal mode is reported. The two main aims are to explore the effects of rotational buoyancy on the flow development and to assess the ability of available turbulence models to predict such flows. Two test cases have been computed corresponding to values of the rotation number, Ro, of 0.12 and 0.24, which are typical of operating conditions in internal cooling passages of gas turbine blades. Computations from three turbulence models are presented: a k–ε eddy viscosity (EVM) model matched to a low-Reynolds-number one-equation EVM in the near-wall region; a low-Re k–ε EVM and a low-Re algebraic stress model (ASM). Additional computations in which the fluid density is assumed to remain constant allow the distinct contributions from buoyancy and Coriolis forces to be separated. It is thus shown that rotational buoyancy can have a substantial influence on the flow development and that, in the case of outward flow, it leads to a considerable increase of the side-averaged heat transfer coefficient. The Coriolis-induced secondary motion leads to an augmentation of the mean heat transfer coefficient on the pressure surface and a reduction on the suction side. The k–ε/one-equation EVM produces a mostly reasonable set of heat transfer predictions, but some deficiencies do emerge at the higher rotation number. In contrast, predictions with the low-Re k–ε EVM return a spectacularly unrealistic behavior while the low-Re ASM thermal predictions are in encouragingly close agreement with available measurements.

Prediction of Heat Transfer For Turbulent Flow in Rotating Radial Duct

The objective of the current modeling effort is to validate the numerical model and improve upon the prediction of heat transfer in rotating systems. Low‐Reynolds number turbulence model (without the wall function) has been employed for three‐dimensional heat transfer predictions for radially outward flow in a square cooling duct rotating about an axis perpendicular to its length. Computations are also made using the standard and extended high‐Reynolds number kturbulence models (in conjunction with the wall function) for the same flow configuration. The results from all these models are compared with experimental data for flows at different rotation numbers and Reynolds number equal to 25,000. The results show that the low‐Reynolds number model predictions are not as good as the high‐Re model predictions with the wall function. The wall function formulation predicts the right trend of heat transfer profile and the agreement with the data is within 30% or so for flows at high rotation number. Since the Navier‐Stokes equations are integrated all the way to wall in the case of low‐Re model, the computation time is relatively high and the convergence is rather slow, thus rendering the low‐Re model as an unattractive choice for rotating flows at high Reynolds number.The extended k‐ε turbulence model is also employed to compute heat transfer for rotating flows with uneven wall temperatures and uniform wall heat flux conditions. The comparison with the experimental data available in literature shows that the predictions on both the leading wall and the trailing wall are satisfactory and within 5‐25% agreement.

The 10-μm Bands of the 17O3 Isotopic Species of Ozone

Using high-resolution (R ∼ 0.002 cm−1) Fourier transform spectra of ozone containing about 20% of 17O3 isotopic species, it has been possible to observe and assign the {ν1, ν3} bands of 17O3 up to very high rotational quantum numbers. For this analysis, we used the ground state energy levels calculated from the (000) rotational constants obtained for 17O3 in a recent microwave study performed by J.-M. Colmont (submitted for publication). Then, from the {(100), (001)} rotational energy levels derived in the present work, a set of molecular parameters (vibrational band centers and rotational and coupling constants) for the {(100), (001)} interacting states of 17O3 has been determined using a Hamiltonian matrix which explicitly takes into account the (100) ↔ (001) Coriolis interaction. Finally, using transition moments derived theoretically from those of 16O3, a synthetic spectrum (line positions and intensities) of the ν1 and ν3 bands has been generated.

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of photolytically generated hot CF radicals

Abstract In this paper, we investigate the rotationally resolved spectra of hot CF radicals generated after IR multiphoton dissociation (IRMPD) of CFCl 3 or CF 2 Cl 2 and subsequent UV photodissociation. It is shown that these conditions are advantageous for the spectroscopy of transitions involving high rotational quantum numbers and hot bands. Thus molecular constants of CF for the first vibrationally excited state of the electronic ground state ( A v =77.1 cm −1 , B v =1.389 cm −1 , D v =6.570×10 −6 cm −1 ) are determined for the first time or are calculated more accurately. The spectroscopic method used was resonance-enhanced multiphoton ionization (REMPI) spectroscopy.