Cylindrical Holes Research Articles

The film cooling performance of spiral-channel holes on turbine guide vane

A spiral-channel hole is implemented to heighten the cooling performance of turbine vanes by inducing swirling flow. Numerical simulations examine and compare the film effectiveness and flow structure at four positions. The impact of various factors, such as blowing ratio, hole position, and mainstream Reynolds numbers, on film effectiveness is studied. The spiral-channel hole provides superior cooling effect compared to the cylindrical hole on the suction and pressure sections. When M is 0.5, the coverage range of the spiral-channel hole, where film cooling effectiveness exceeds 0.25, is twice as large as that of the cylindrical hole. The cooling performance difference between the two types of holes is minimal at the leading edge of the turbine vane. The optimal blowing ratio for the spiral-channel hole to achieve maximum cooling performance is 2.0. The groove structure on the inner wall of the spiral-channel hole induces numerous vortices, which deflect the streamlines inside the spiral channel, improving the adhesion of the coolant to the vane surface. The local radial pressure gradient at the outlet suppresses the coolant flow, enhancing its adhesion to the vane surface. The acceleration effect resulting from the streamwise pressure gradient reduces the mixing speed of the fluids. Collectively, these effects enhance the film effectiveness. Increasing Reynolds numbers expands the transverse coverage region of the mixed fluid. But it also lowers the temperature of the cooling film. The dominant impact of Reynolds numbers on film cooling effectiveness depends on which of the above-mentioned factors is most significant.

Goufo-Caputo fractional viscoelastic photothermal model of an unbounded semiconductor material with a cylindrical cavity

In order to describe the photothermal dynamic behavior of viscoelastic semiconductor materials, the authors of this work propose a fractional modification of the Kelvin-Voigt type. The generalized Mittag-Leffler function method with two parameters was utilized as the non-local, nonsingular kernel of the Goufo-Caputo fractional operator, which is similar to the AB fractional derivative. Also, a new concept of photovoltaic heat transfer has been developed to describe the process of photothermal heating in semiconductors, in which light energy is converted into thermal energy by absorption. This unique model is grounded in the theoretical framework of the Moore-Gibson-Thompson (MGT) equation, and it offers additional insights into the underlying process of light sensitive heat transfer, as well as the intricate interaction between heating signals, elasticity, and plasma. As a direct application of the proposed model, the photothermal interactions that occur when an infinitely rotating semiconductor material with a cylindrical hole is subjected to a laser thermal flux and immersed in a constant axial magnetic field have been investigated. These findings may have implications for developing optically absorbent nanostructures and their use in photothermal energy generation. For this reason, the comparison of modified photoelasticity models with spherical derivatives and classical models applied to semiconducting materials seems interesting.

Analysis of Water Volume Required to Reach Steady Flow in the Constant Head Well Permeameter Method

The most common method for in situ measurement of saturated hydraulic conductivity (Ksat) of the vadose zone is the constant head well permeameter method. Our general objective is to provide an empirical method for determining volume of water required for measuring Ksat using this procedure. For one-dimensional infiltration, steady state reaches as time (t) → ∞. For three-dimensional water flow from a cylindrical hole under a constant depth of water, however, steady state reaches rather quickly when a saturated bulb forms around the hole. To reach a quasi-steady state for measuring Ksat, we assume an adequate volume of water is needed to form the saturated bulb around the hole and increase the water content outside of the saturated bulb within a bulb-shaped volume of soil, hereafter, referred to as wetted soil volume. We determined the dimensions of the saturated bulb using the Glover model that is used for calculating Ksat. We then used the values to determine the volume of the saturated and wetted bulbs around the hole. The volume of water needed to reach a quasi-steady state depends on the difference between the soil saturated and antecedent water content (Δθ). Based on our analysis, between 2 and 5 L of water is needed to measure Ksat when Δθ varies between 0.1 and 0.4 m3 m−3, respectively.

A Scaling Relation for Cryoconite Holes

AbstractTiny cryoconite holes are commonly found on glacier surfaces. Despite a long history of research on them, their influence on glacier‐scale mass balance and runoff are not well understood. We model the absorption of solar radiation at the bottom of cylindrical cryoconite holes, incorporating the three‐dimensional geometry. The simulated holes achieve a limiting steady‐state depth, where the daily melt rate at the bottom of the holes matches that at the glacier surface. This implies a feedback loop restricting the excess ice melt due to the presence of dark supraglacial impurities. The modeled steady‐state depth scales approximately linearly with the radius, consistent with in situ observations at several glaciers across the world. Given the areal coverage and radius distribution of cryoconite holes on a glacier, this scaling yields first‐order estimates of their melt contribution.

The Effects of Channel Supplies on Overall Film-Cooling Effectiveness

Abstract Cooling components in the hot section of a gas turbine are essential to component durability. Common methods of cooling include rib turbulators in internal passages and film cooling on external surfaces. The holes that produce the film cooling are fed from the internal channels often containing ribs. Consequently, there is an interdependence of internal heat transfer and external film cooling. The purpose of this study was to obtain a better understanding of the interaction of ribs and film cooling. To quantify the cooling performance, the surface temperatures were measured, from which overall effectiveness was calculated. For the experiments, additively manufactured test coupons were made of Inconel 718 to match engine Biot numbers. These test coupons had internal feed channels with and without ribs and had both cylindrical holes and meter-diffuser-shaped holes with 15 deg lateral expansion angles and a 1 deg forward expansion angle. A single rectangular channel was one type of feed channel. The other type of feed channel was individual circular channels, with each circular channel supplying an individual film-cooling hole. The experimental results showed that the circular individual channels have 80% higher baseline overall effectiveness than the single rectangular channels without any film cooling. Ribbed turbulators without film cooling also increased the overall effectiveness by 21% for single rectangular channels and by 29% for the circular individual channels compared to the respective non-ribbed channels. While the film cooling increased the overall effectiveness of all geometries, the single rectangular channels had increased overall effectiveness levels by up to twice that of the no film-cooling case. On average, the single rectangular channels had an 80% improvement from film cooling, whereas the individual channel feeds, on average, had only a 50% improvement, given their high baseline effectiveness levels.

Comparisons of Overall Performance Among Double-Jet Film Cooling Holes, Cylinder Holes, and Fan-Shaped Holes

Abstract In this paper, the film-cooling effectiveness (η) and heat transfer coefficient (h) of different film hole geometries are investigated, including double-jet film cooling (DJFC) holes, streamwise cylindrical holes, and fan-shaped holes, both experimentally and numerically. Results reveal that when the blowing ratio is less than 1.0, the DJFC holes have the highest η and the highest h, as well as the highest net heat flux reduction (NHFR). However, a higher blowing ratio (>1.0) leads to a quickly decreasing NHFR of DJFC holes. The asymmetric antikidney vortex and the high turbulent kinetic energy (TKE) are dominant in the performance of the DJFC holes. Owing to medium effectiveness and the lowest heat transfer coefficient, the fan-shaped holes possess the highest net heat flux reduction at M = 2.0 although the value is negative. The relatively weak kidney vortex and the low TKE can explain the phenomena. The cylindrical holes have the lowest η and the lowest NHFR due to the kidney vortex and relatively higher TKE.

Study on the effect of waveform film holes on film cooling efficiency

In order to improve the film cooling efficiency of the cooling gas on the hot side wall of the plate, the flow field, temperature field and the average film cooling efficiency of the cylindrical hole, rectangular hole and waveform hole near the wall were compared and analyzed by numerical calculation method. Compared with cylindrical holes, the average spanwise film cooling efficiency of rectangular hole is improved by 100%, and the average spanwise film cooling efficiency of waveform hole is improved by 130%. In addition, the effects of the amplitude A of the waveform hole and the initial phase ϕ on the cooling efficiency are compared and analyzed. The results show that: Within the scope of this study, when the blowing ratio M = 1, lifting the initial phase ϕ of the waveform hole can effectively improve the film cooling efficiency of the cooling gas on the wall. When the amplitude A of the waveform hole is raised, the film cooling efficiency of the cooling gas on the wall will first increase and then decrease, reaching the maximum at the amplitude A = 0.4D. At low blowing ratio, the geometric structure of waveform hole has little influence on the cooling effect of wall surface. Under high blowing ratio, when the geometric structure of waveform hole is changed, the influence of secondary flow on the average spanwise cooling efficiency of wall surface is great.

Experimental and numerical investigations of vane endwall film cooling with different cooling hole configurations

In the present study, measurements are conducted to investigate endwall film cooling and its secondary effect on airfoil surfaces in a linear cascade. Validated numerical simulations are performed to obtain flow fields. Several configurations of upstream double-row cylindrical holes with an inclination angle (α) of 30 deg are studied, including streamwise holes, compound-angled holes, and double-jet film-cooling (DJFC) holes. The effects of blowing ratios ranging from 0.5 to 2.0 are also considered. Results indicate that at lower blowing ratios, strong secondary flows dominate the flow field and lead to weak coolant coverage on the endwall and the airfoil surfaces. The differences amongst the configurations are not obvious due to the insufficient coolant momentum. At higher blowing ratios, the film cooling performance on the endwall and the airfoil surfaces is greatly improved. Moreover, the effect of cooling configuration becomes more apparent as the blowing ratio increases, which determines the distribution of coolant coverage, especially on the airfoil surfaces.

Numerical investigation of the rotating detonation engine with cat-ear-shaped film cooling holes under varying operating modes

The advancement of implementing the rotating detonation engine (RDE) in practical applications necessitates overcoming the challenges arising from severe heating and high-frequency thermal loads caused by the rotating detonation wave (RDW). As an important means of thermal protection, film cooling is widely used in modern gas turbines. In this numerical study, film cooling holes with a cat-ear-shaped configuration are arranged on the outer wall of the RDE, which operates in various modes with a different number of RDWs. It is shown that as the number of RDWs increases in the flow field, the intensity of each RDW gradually decreases but the interactions between the cooling air (secondary flow) and the RDWs become more frequent. These phenomena can lead to noticeable differences in the characteristics of the secondary flow and the corresponding film cooling performance across different operating modes. Specifically, the analysis reveals the influence of the number of RDWs on the development and oscillation of the secondary flow jet. A comprehensive assessment of the effectiveness of the cat-ear-shaped and cylindrical film holes is also conducted in terms of the film cooling efficiency, i.e., the overall efficiency and the variation of the cooling efficiency along the axial direction, the coverage of cooling air on the wall surface, and the fluctuation of the secondary flow under the periodic influence of the high-pressure RDW.

Experimental Study of Two Rows Hybrid Film Cooling Holes Over Flat Plate Surface Using IR Technology

The study examines the effectiveness of two rows of hybrid film cooling holes over a plate surface using infrared technology and a thermal wind tunnel. The two rows consist of seventeen coolant injection holes, with nine in the first row and eight in the second row. Two cases were studied: case 1 using cylindrical holes and case 2 using hybrid holes. Both cases had the same cross-sectional area with a hydraulic diameter of 5.3 mm and a forward coolant injection angle of 30° in the streamwise direction. Different blowing ratios (mass flows ratio between the coolant and mainstream) were tested at 0.5, 1.0, and 1.5. The study focuses on evaluating the impact of hole shape with various blowing ratios on film cooling effectiveness. In addition, thermal images of the test surface were taken via an infrared camera after reaching a steady state. The results indicated that at a blowing ratio of 0.5, there was a significant enhancement in film efficacy, with a decrease in the test surface temperature of the cylinder and hybrid hole cases by 31.8% and 35.0%, respectively, when compared to a blowing ratio of 1.0 and 1.5, which had a temperature increase. Therefore, the film cooling effectiveness decreased to 30.9% and 32.4%, and 29.5% and 31.7% for the cylinder and hybrid hole cases, respectively. Additionally, the better overall film cooling effectiveness in this study was achieved by the configuration of the hybrid holes at a blowing ratio of 0.5, which resulted in a film cooling effectiveness of 35.0%

Modeling of electrochemical micromachining of cylindrical hole surface by eccentric cathode

Modeling of electrochemical micromachining of cylindrical hole surface by eccentric cathode

Aircraft engine nozzle guide vane surface temperature optimization

An optimization method based on the sensitivity of global and local geometric parameters is proposed to improve the cooling efficiency of E3 engine nozzle guide vane. For 29 geometric parameters that affect the vane maximum temperature in the cooling design, the sensitivity ranking of them is firstly obtained by the DOE method. Then the most influential parameters including the diameter or location of the film cooling hole are selected as the optimization variables to decrease the maximum surface temperature of the nozzle guide vane. On this basis, to further reduce the local temperature downstream the pressure side, a new duck-paw type film cooling hole is applied. The duck-paw type film cooling hole was produced with the adjoint method through identifying the sensitivity of the geometric boundary parameters of the film cooling holes. Compared to the cylindrical holes, the duck-paw shaped film cooling hole can greatly improve the cooling efficiency under the same conditions. The duck-paw type film cooling holes are applied to the last two rows of film cooling holes located on the pressure side of nozzle guide vane. Three-dimensional conjugate flow and heat transfer analysis results show that the maximum temperature of the optimized cooling structure vane is reduced by 39K, and the average temperature decreases by nearly 20K.

Impact of external turbulence on film cooling designs using large eddy simulations

Large Eddy Simulations (LES) of film cooling flows were conducted to investigate the impact of high turbulence intensity in the main flow, representative of jet-engine combustor conditions. A comparison was made with LES simulations at zero turbulence at the main flow inlet boundary. The study investigated three different film cooling configurations, which involved cylindrical holes and two variations with holes embedded in trenches known as transverse and segmented trench. Different momentum ratios (I=3.5 and 8.3) relevant to combustor flows in jet-engines were applied. The LES simulations utilized OpenFOAM and solved the energy and passive scalar transport equations to determine film cooling efficiency (η), heat transfer coefficient (hf), and net heat flux reduction (NHFR). The numerical results were validated through comparison with experimental data. The mean and instantaneous results revealed that high turbulence intensity in the main flow significantly influenced film cooling performance. The film cooling efficiency was found to decrease with increased turbulence intensity, while for the ordinary film cooling design exhibiting jet lift-off, the increased mixing led to higher η. The heat transfer coefficient increased with turbulence intensity and momentum ratio, with turbulence intensity having a greater impact on ordinary designs and momentum ratio on trenched designs. Moreover, increasing turbulence intensity or momentum ratio resulted in lower NHFR for all designs. Hot spots were observed in the instantaneous results, with spatial variations depending on the film cooling design.

Investigation of aerothermal performance of blade tip with conical holes in transonic flow

The blade tip with conical holes is proposed in the current paper to improve the film cooling performance on the turbine blade tip. The film cooling performance of the blade tip with cylindrical holes is studied as a reference case. The pressure sensitive paint technique is adapted to obtain the tip film cooling effectiveness in transonic flow. The numerical simulation is used to obtain the tip flow field and aerodynamic loss. The cascade exit Mach number and inlet Reynolds number are 1.05 and 370000, respectively. The experiment and calculation are carried out at two tip clearance gaps of 0.7% and 1.5% and four mass-flow-ratios. The results show that at low mass flow ratios, the film cooling effectiveness of the blade tip with conical holes is significantly higher than that of the blade tip with cylindrical holes at the tip mid-chord region. Increasing the tip clearance gap from 0.7% to 1.5% shows a negative effect on the film cooling performance of the blade tip with conical holes in the tip mid-chord region, particularly for the low mass flow ratio. The pitch-wise averaged aerodynamic loss coefficient of the blade tip with cylindrical holes is lower than that of the blade tip with conical holes near the shroud.

Modelling the development and decay of cryoconite holes in northwestern Greenland

Abstract. Cryoconite holes (CHs) are water-filled cylindrical holes with cryoconite (dark-coloured sediment) deposited at their bottoms, forming on ablating ice surfaces of glaciers and ice sheets worldwide. Because the collapse of CHs may disperse cryoconite on the ice surface, thereby decreasing the ice surface albedo, accurate simulation of the temporal changes in CH depth is essential for understanding ice surface melt. We established a novel model that simulates the temporal changes in CH depth using heat budgets calculated independently at the ice surface and CH bottom based on hole-shaped geometry. We evaluated the model with in situ observations of the CH depths on the Qaanaaq ice cap in northwestern Greenland during the 2012, 2014, and 2017 melt seasons. The model reproduced the observed depth changes and timing of CH collapse well. Although earlier models have shown that CH depth tends to be deeper when downward shortwave radiation is intense, our sensitivity tests suggest that deeper CH tends to form when the diffuse component of downward shortwave radiation is dominant, whereas CHs tend to be shallower when the direct component is dominant. In addition, the total heat flux to the CH bottom is dominated by shortwave radiation transmitted through ice rather than that directly from the CH mouths when the CH is deeper than 0.01 m. Because the shortwave radiation transmitted through ice can reach the CH bottom regardless of CH diameter, CH depth is unlikely to be correlated with CH diameter. The relationship is consistent with previous observational studies. Furthermore, the simulations highlighted that the difference in albedo between ice surface and CH bottom was a key factor for reproducing the timing of CH collapse. It implies that lower ice surface albedo could induce CH collapse and thus cause further lowering of the albedo. Heat component analysis suggests that CH depth is governed by the balance between the intensity of the diffuse component of downward shortwave radiation and the turbulent heat transfer. Therefore, these meteorological conditions may be important factors contributing to the recent surface darkening of the Greenland ice sheet and other glaciers via the redistribution of CHs.

Unveiling particle deposition characteristics on flat plate with a shaped film cooling hole

Particle deposition on turbine blades poses a significant challenge to the safe operation of gas turbines. The blockage of film-cooling holes and alteration in the aerodynamic shape of blades affect the turbine's efficiency, highlighting the importance of reducing particle deposition on turbine blades. To investigate the characteristics and potential mechanisms of deposition, experimental and numerical studies were conducted on two typical film-cooling holes: cylindrical and 777-shaped. A multi-perspective scanning method was used to measure the three-dimensional deposition topography on flat plates under a particle-laden environment. The wax deposition experiments showed that the deposition thickness of both holes increased with the blowing ratio. However, the 777-shaped hole exhibited a 10–40% reduction in deposition compared with the cylindrical hole. The computational predictions of deposition patterns agreed well with the experimental results. The numerical simulations revealed that the presence of film cooling reduced deposition in some areas but increased deposition in the vicinity of the film coverage region owing to the entrainment of vortices. Overall, this study further elucidates particle deposition characteristics and the influencing factors, which can guide the design of blade cooling systems with reduced deposition.

Budgets of Reynolds stresses in film cooling with fan-shaped and cylindrical holes

The compressible budget terms in the transport equations of Reynolds stresses are examined from the large eddy simulation (LES) result of the film cooling. The capability of LES and the statistical post-processing procedure were first validated. The compressible Reynolds stress budget terms are then analyzed for both fan-shaped and cylindrical cooling films. The balance of all budget terms is shown. The effect of the blowing ratio on each budget term is examined. The mechanisms by which energy is extracted from the mean flow and distributed among the normal Reynolds stresses are highlighted. The sources of anisotropy in the Reynolds stress distributions are examined in detail, and their relation to the flow patterns of the mean and instantaneous flow is explored. The downstream development of the Reynolds stress budgets is studied, and it is shown that the jets of both fan-shaped and cylindrical films can be split into a near field and a far field with different properties. Far downstream of the cooling films, the Reynolds stress budgets near the wall present similarities with the Reynolds stress budgets in a boundary layer, while the Reynolds stress budgets further away from the wall resemble budgets in a free-shear flow. It is shown that the budgets of the Reynolds stress in the three-dimensional wall jets object of this study obey approximate similarity laws. These laws are based on easily obtained integral scales but need to be modified by suitable powers of the distance from the orifice producing the jet.

Analytical approach to the problem of electromagnetic wave scattering by a cylindrical hole in a thin metal screen

A method of analytical study of a metal film perforated by cylindrical nanoholes as the basis of a metasurface has been proposed. The formulas deduced completely determine the electromagnetic field of a wave scattered by the hole at any distance from the surface. The calculation of the transmission and absorption spectra of the studied structure, as well as the dependence of the phase of the scattered wave on the radius of the hole, is carried out using analytical formulas. The calculation results are consistent with the literature data for calculating the efficiency of a quantum photodetector and the phase change interval of light scattered by meta-atoms required for lens design.

Influence of Spatial Characteristic Parameters of Film Cooling Holes on the Strength of Turbine Blade

In order to improve the fatigue resistance of turbine blades with special-shaped film cooling holes in real working environments, the spatial geometric characteristics of the gas film holes are studied by using the numerical calculation method of gas-thermal-solid depth coupling, which is based on the spatial geometric characteristics of special-shaped film cooling holes. Then, the influence of stress level and durable strength at the hole edge is developed, which includes the parameters of the film jet angle, the flow direction divergence angle, the span-wise divergence angle, and the pore diameter on the film cooling holes. The results show that the flow direction expansion angle and the spanwise expansion angle are the most significant impacts on the hole edge stress at the same pore diameter and film jet angle. Compared with the cylindrical gas film hole, it is decreased by about 9.3% to 25.8%, which is the hole edge equivalent stress of the special-shaped gas film hole. The durable strength of the hole edge increases by about 11.1% to 25.2%.

ON THE FEATURES OF THE CHARACTERISTICS OF THE SPECTRUM AND PULSE OF THE ECHO SIGNAL DURING ULTRASONIC CONTROL OF METAL THROUGH THE FUSED LAYER BY ANGLE BEAM LONGITUDINAL WAVE PROBES

Based on computer simulation of an echo signal from a side drilled hole type reflector during ultrasonic control of the base metal by an angle beam longitudinal wave probe with nominal frequency of 1.8 MHz through transversal-isotropic elastic layer of constant thickness at different values of the anisotropy parameter, it is shown that with an increase in the anisotropy parameter there is a shift of the signal maximum in the direction of increasing the distance to the reflector, which is associated with an increase in the phase velocity of the quasi-longitudinal wave in the layer, and an increase in the maximum value due to a change in the double transformation coefficient when the longitudinal wave passes from the prism of the probe to the layer and back. For a probe with a frequency of 2.5 MHz, an increase in the anisotropy parameter leads to a decrease in the value of the echo maximum, since the increased increase in the attenuation of the quasi-longitudinal wave in the layer is not compensated by a change in the double transformation coefficient. For different nominal angles of probe (45…60°), a noticeable change in the shapes of frequency spectra and echo pulses at different values of the anisotropy parameter has not been established. The effect of increasing the distance from the control surface to the axis of the cylindrical hole at a constant layer thickness on the change of the amplitude of the echo signal in the calculated range of values of the anisotropy parameter is shown.