Hot Streak Research Articles

Mid-career pitfall of consecutive success in science.

The creativity of scientists often manifests as localized hot streaks of significant success. Understanding the underlying mechanisms of these influential phases can enhance the effectiveness of support systems and funding allocation, fostering groundbreaking discoveries worthy of accolades. Historically, analyses have suggested that hot streaks occur randomly over time. However, our research, through meticulous examination, reveals that these phases are not flatly distributed but are more frequent at the early and late stages of scientists' careers. Notably, both early and late hot streaks are marked by dense tie collaborations, with the former typically involving close partnerships with particular authors and the latter being characterized by involvement in large-scale projects compared with single-top or ordinary papers. This pattern indicates that mid-career researchers lack both intimate relations and resources to keep big projects, leading to "mid-career pitfall" of consecutive success. This insight holds profound implications for the development of policies and initiatives aimed at bolstering innovative research and discovery.

Experimental and numerical studies on hot streak transportation and attenuation in a 1.5-stage turbine

Experimental and numerical studies on hot streak transportation and attenuation in a 1.5-stage turbine

Numerical investigation on the influence of swirl number to high-temperature zone evolution and outlet temperature distribution in multi-stage combustor

The outlet temperature distribution plays a crucial role in determining the lifespan and stability of downstream thermal components. It poses a significant challenge in the design and regulation of high-temperature combustors. This study aims to investigate the influence of swirl number on the outlet temperature distribution in multi-stage combustor. The impact of varying fourth-stage swirl numbers on flow structure, hot streaks, and temperature distribution is compared and analyzed. The results indicate that increasing the swirl number significantly improves the air–fuel mixing within the combustion zone, leading to the expansion of high-temperature regions. Additionally, the high-temperature region migrates upstream along the primary zone. With an increase in the swirl number, the relative area of hot spots within the combustor also increases. Remarkably, the swirler configuration with a swirl number of 1.5 exhibits the most minimal exit temperature gradient and the highest level of temperature distribution uniformity, quantified by an outlet temperature distribution factor (OTDF) of 0.26. Furthermore, changes in the swirl number affect the distribution of combustion modes within the combustor. Increasing the swirl number promotes the premixed combustion mode at the pilot stage exit and enhances temperature uniformity at the swirler exit. Thorough comprehension of the temperature distribution in the primary zone enables control of the outlet temperature distribution from its origin. Uniformity amplitude (UA) of HCO and primary temperature distribution factor (PTDF) are defined to describe the temperature distribution in primary zone. At a swirl number of 1.5, the UA and PTDF also shows the lowest values of 0.2754 and 0.3019, respectively. Overall, when improving the distribution of HCO under both premixed and non-premixed modes, a more uniform temperature distribution across the primary zone can be achieved, effectively optimize the exit temperature distribution.

Film hole layout optimization for multi-row film cooling plate in continuous parameter space under non-uniform inlet temperature distribution

Film cooling is an advanced external cooling technology for protecting gas turbine blades from excessive temperatures. To counteract non-uniform heat loads caused by hot streak and swirl effects at the combustion chamber outlet, fine design of film hole positions is necessary. However, the complexity due to the numerous film holes and their positional parameters presents challenges in the independent optimization of film hole positions in a continuous parameter space. This study proposed an optimization method grounded in the divide and conquer approach to address optimization for film hole layout. The film hole layout was decomposed into multiple single rows and optimized systematically by iteratively refining the single-row film hole layout along the streamwise direction using the expectation maximization algorithm. Optimized layouts for five different inlet temperature distributions were obtained using the proposed method and adiabatic wall temperature distributions were compared and analyzed for optimized and staggered layouts. Additionally, the cooling performance of the optimized layout was evaluated against the staggered layout under conjugate heat transfer conditions and the robustness of the optimized layout under various blowing ratios and peak temperature positions was tested. The results demonstrated that the proposed method can optimize the positions of 52 film holes within 0.3h, and it was generalized to various inlet temperature distributions. By enhancing lateral interactions among downstream film jets, the lifting effect of kidney vortex in the optimized layout was weakened, bringing the film jets closer to the wall and significantly increasing coolant coverage during streamwise development. Comparative analysis reveals the superior cooling performance of the optimized layout at the blowing ratio of 1.0, evidenced by a 15.1% reduction in total input heat transfer rate and a 12.3% enhancement in overall cooling efficiency relative to the staggered layout. Under conditions with blowing ratios ranging from 0.5 to 1.5 and peak temperature position deviations, the average wall temperature of the optimized layout consistently remained lower than the staggered layout, indicating the robustness of the optimized layout to variations in blowing ratio and hot streak position.

Transition delay in a Mach 6 boundary layer using steady blowing and suction strips

Direct numerical simulations (DNS) were carried out to investigate flow control for transition delay using steady blowing/suction strips at the wall of a flared cone at Mach 6 and zero angle of attack. For the numerical investigations of the transition control strategy, the flared cone geometry and the flow conditions of the experiments in the Boeing/Air Force Office of Scientific Research (AFOSR) Mach 6 Quiet Tunnel (BAM6QT) at Purdue University were chosen. For the DNS, transition was initiated by introducing random disturbances at the inflow of the computational domain, emulating ‘natural’ transition in wind-tunnel experiments caused by free-stream noise. In both wind-tunnel experiments and numerical simulations, streamwise ‘hot’ streaks were found on the surface of the flared cone, which are caused by a nonlinear interaction of an axisymmetric second-mode wave and a pair of oblique waves of the same frequency (‘fundamental resonance’). The objective of the flow control strategy proposed here is to delay the transition onset, and thus mitigate the negative consequences associated with the nonlinear transition stages, i.e. the development of hot streaks and large wall-pressure amplitudes that were observed in experiments and DNS. Our previous so-called ‘controlled’ transition simulations have shown that flow control using steady blowing and suction strips can lead to a significant delay of the hot streak development on the surface of the flared cone. The simulation results presented in this paper show that this flow control strategy remains effective, even in a natural transition scenario characterized by broadband disturbances.

Experimental Investigation of the Sensitivity of Forced Response to Cold Streaks in an Axial Turbine

In turbomachinery, geometric variances of the blades, due to manufacturing tolerances, deterioration over a lifetime, or blade repair, can influence overall aerodynamic performance as well as aeroelastic behaviour. In cooled turbine blades, such deviations may lead to streaks of high or low temperature. It has already been shown that hot streaks from the combustors lead to inhomogeneity in the flow path, resulting in increased blade dynamic stress. However, not only hot streaks but also cold streaks occur in modern aircraft engines due to deterioration-induced widening of cooling holes. This work investigates this effect in an experimental setup of a five-stage axial turbine. Cooling air is injected through the vane row of the fourth stage at midspan, and the vibration amplitudes of the blades in rotor stage five are measured with a tip-timing system. The highest injected mass flow rate is 2% of the total mass flow rate for a low-load operating point. The global turbine parameters change between the reference case without cooling air and the cold streak case. This change in operating conditions is compensated such that the corrected operating point is held constant throughout the measurements. It is shown that the cold streak is deflected in the direction of the hub and detected at 40% channel height behind the stator vane of the fifth stage. The averaged vibration amplitude over all blades increases by 20% for the cold streak case compared to the reference during low-load operating of the axial turbine. For operating points with higher loads, however, no increase in averaged vibration amplitude exceeding the measurement uncertainties is observed because the relative cooling mass flow rate is too low. It is shown that the cold streak only influences the pressure side and leads to a widening of the wake deficit. This is identified as the reason for the increased forcing on the blade. The conclusion is that an accurate prediction of the blade’s lifetime requires consideration of the cooling air within the design process and estimation of changes in cooling air mass flow rate throughout the blade’s lifetime.

Decoding the News Media Diet of Disinformation Spreaders.

In the digital era, information consumption is predominantly channeled through online news media and disseminated on social media platforms. Understanding the complex dynamics of the news media environment and users' habits within the digital ecosystem is a challenging task that requires, at the same time, large databases and accurate methodological approaches. This study contributes to this expanding research landscape by employing network science methodologies and entropic measures to analyze the behavioral patterns of social media users sharing news pieces and dig into the diverse news consumption habits within different online social media user groups. Our analyses reveal that users are more inclined to share news classified as fake when they have previously posted conspiracy or junk science content and vice versa, creating a series of "misinformation hot streaks". To better understand these dynamics, we used three different measures of entropy to gain insights into the news media habits of each user, finding that the patterns of news consumption significantly differ among users when focusing on disinformation spreaders as opposed to accounts sharing reliable or low-risk content. Thanks to these entropic measures, we quantify the variety and the regularity of the news media diet, finding that those disseminating unreliable content exhibit a more varied and, at the same time, a more regular choice of web-domains. This quantitative insight into the nuances of news consumption behaviors exhibited by disinformation spreaders holds the potential to significantly inform the strategic formulation of more robust and adaptive social media moderation policies.

Does Smart Money Believe in the Hot Hand? Evidence From Daily Fantasy Baseball

The behavior of informed traders, or “smart money,” in sports betting markets has long been of interest to researchers. In this paper, we focus specifically on the behavior of smart money in Major League Baseball (MLB) daily fantasy sports (DFS) contests to determine whether they avoid cognitive-behavioral biases to increase their expected earnings. Specifically, we investigate whether smart money avoids the hot hand bias, where individuals tend to overestimate the likelihood of success for players on a hot streak. Using a dataset of MLB DFS contests, we find that winning lineups have lower usage rates for players exhibiting the hot hand compared to losing lineups. This suggests that smart money identifies and fades the hot hand strategy to increase their expected earnings.

Exploring the boundary layer transition of hypersonic flow over a compound delta wing

The boundary layer transition on a compound delta wing for Mach 6 has been studied experimentally and numerically. The experiment was performed at Peking University quiet wind tunnel using the Rayleigh scattering flow visualization and infrared thermography. Direct numerical simulations, under the same flow conditions, are applied to analyze the transition mechanism. The results show that the traveling cross flow vortices first appear near the leading edge of compound delta wing. These vortices modulate the mean profile of the flow due to which a rope-like structure appear in the streamwise direction, which is typical of Mack's second-mode. As Mack's second-mode grows to a sufficiently large amplitude, it triggers secondary instability, which behaves as secondary finger like structures. At the end of the transition process, low-frequency waves are excited by Mack's second-mode through an interaction mechanism with their phase speed approaching each other. It is also found that increasing the unit Reynolds number greatly promotes the aerodynamic heating as well as local hot streaks appear on both sides of the compound delta wing in the streamwise direction. The appearance of hot streaks on the compound delta wing is strongly correlated with Mack's second-mode.

Analysis and Modeling of Turbulence Anisotropy of a Swirled Hot Streak Flow

Abstract This study is carried out in the context of hot streak flows in high-pressure turbines, for which a correct prediction of the temperature evolution is required. The present work particularly focuses on the turbulence anisotropy analysis of a swirled hot streak flow in a bent channel representative of a nozzle guide vane (NGV) passage of a high-pressure turbine. Large-eddy simulations are conducted with the in-house solver IC3 in order to measure and characterize the anisotropy of turbulence. Moreover, to evaluate turbulence modeling, steady simulations of the bent channel are performed with the elsA software, which solves the Reynolds-averaged Navier–Stokes (RANS) equations. LES is first used to complete a turbulent kinetic energy (TKE) budget that enables to understand the energetic transfers associated with turbulence. This budget reveals two distinct zones where turbulence activity is impacted when the curvature is reached. The analysis of the anisotropy of turbulence based on two metrics highlights a misalignment of the Reynolds stress tensor and the mean strain-rate tensor (Schmitt's criterion), and a strong anisotropy developing inside the bent duct (Lumley's analysis) that may cause the failure of the classical RANS turbulence models based on Boussinesq's hypothesis. To check this hypothesis, RANS is positioned against LES with different turbulence models that accounts or not for the anisotropy of turbulence. Both turbulence activity (TKE budgets, Lumley's analysis) and aerothermal fields (radial distributions) are compared. Results show that Explicit Algebraic Reynolds Turbulence Models (EARSM) enable to better account for the anisotropy of turbulence, which in turn promote a better prediction of temperature, both in terms of intensity and trajectory.

Comparison of Showerhead Film Cooling and Double Wall Cooling in a Guide Vane Leading Edge with Hot Streak

Comparison of Showerhead Film Cooling and Double Wall Cooling in a Guide Vane Leading Edge with Hot Streak

Analysis of the thermal insulation performance of turbine blade thermal barrier coatings considering inlet non-uniformity

The gases discharged from the new generation of lean-burn combustors usually have hot streaks (HS) and swirls. The thermal performance of rotor thermal barrier coatings (TBCs) exhibits significant non-constant behavior due to inlet non-uniformity and blade row interaction. To investigate the non-constant thermal insulation performance of the blade TBCs, non-constant numerical simulations were carried out for the first stage vane and blade of the High-pressure turbine of the GE-E3 engine. The normalized temperature results for the HS and the combination of HS and swirl cases were compared with the uniform inlet case to investigate the effect of inlet non-uniformity on the surface temperature and thermal insulation effect of the blade TBCs. The results show that a credible investigation of rotor TBCs should consider the unsteady blade row interaction. HS causes high-temperature hot spots on the surface of the TBCs and redistributes them with the change in the direction of the swirl. HS and swirl significantly reduce the turbine blade cooling effectiveness and thermal insulation effectiveness of TBCs. The lowest overall cooling performance of the blades was observed during the 1/4 T stator period. The added swirl reduces the insulation effectiveness's fluctuation value by reducing positive swirl (PSW) by 52.6 % and negative swirl (NSW) by 57.8 %. Therefore, applications and designs of TBCs should consider the effects of HS and swirl.

Modelling of Combustor Non-Uniformities Evolution Through a High-Pressure Turbine Stage

Abstract In modern gas turbines, the reduction of pollutant emissions can be achieved by employing lean-burn combustors. At the combustion chamber outlet, the flow is non-uniform and characterized by a residual swirl superimposed to steady (hot streak) and unsteady (entropy waves) temperature disturbances. During the transport from the combustor outlet to the turbine inlet, these disturbances are weakly dissipated and persist at the turbine inlet. Therefore, the interaction between the combustor non-uniformities and the turbine has to be deeply studied. To study combustor-turbine interaction experimentally, a common practice is to install combustor simulators on non-reactive turbine test facilities. For this purpose, a combustor simulator was designed and installed at Politecnico di Milano turbine test facility. This device can generate a combined steady/unsteady temperature disturbance and swirl profile at the turbine inlet. Using this layout, several experimental campaigns have been carried out changing the type of injected disturbance, the injection position and the turbine operating condition. In this paper, the data collected from these experiments have been used to develop simplified models to predict the transport and dissipation of combustor perturbations through a turbine first stage. In the open literature, few attempts are discussed regarding the modelling of combustor-turbine interaction that - in authors' opinion - represents an important tool for preliminary turbine design.

Influence of Hot Streak and Swirl Clocking Position on Aerothermal Performance of High-Pressure Turbine

In modern civil aeroengines, the hot streak and swirl at the exit of the combustor have a significant impact on the aerothermal performance of the high-pressure turbine (HPT). Due to the different design purposes of the combustor and the turbine, hot streak (HS) and swirl (SW) have different spatial distributions at the turbine inlet. This paper conducts a transient simulation of the GE E3 first-stage HPT, considering the swirl and hot streak facing the middle of the passage and the leading edge of the nozzle guide vane, respectively, and also explores the impact of positive and negative swirl. The results show that different clocking positions and swirl directions will change the incident angle and streamline distribution of the vane, thereby affecting the migration of the hot streak, the temperature and the Nusselt number distribution on the stator surface. In positive cases, the hot streak gathers in the upper part of the passage, and in negative cases, it is in the lower part. In middle cases, high-temperature areas appear in both vanes, and the distributions are opposite. Affected by the swirl, when facing the passage center, the pressure side stagnation lines of the two vanes are also different, so the Nusselt number distribution is opposite. When facing the leading edge, only one vane appears. Due to the insensitive interference of the rotor–stator, the transient migration of the hot streak in the rotor is mainly affected by the inherent secondary flow and the temperature at the inlet of the rotor (especially the conditions facing the leading edge), while the upstream residual swirl is less affected. Unlike the middle case, in leading edge cases, the hot streak is separated and needs to be re-mixed before entering the blade passage, so the temperature change in the blade cascade is relatively gentle. Based on this, the Nusselt number distribution on the surface of the blade is similar. In order to obtain the most favorable operating conditions for the engine, the turbine efficiency is used to compare the aerothermal performance under different conditions. Ultimately, it was found that the turbine with the hot streak and positive swirl directly facing the leading edge was the most efficient.

Hot streak! Inferences and predictions about goal adherence

When do people make optimistic forecasts about goal adherence? Nine preregistered studies find that a recent streak of goal-consistent behavior increases the predicted likelihood that the individual will persist, compared to various other patterns holding the rate of goal adherence constant. This effect is due to perceiving a higher level of commitment following a streak. Accordingly, the effect is larger when the behavior requires commitment to stick with it, compared to when the same behavior is enjoyable in its own right. Furthermore, the effect is weaker in the presence of another diagnostic cue of commitment: when the individual has a high historic rate of goal adherence. People also behave strategically in ways consistent with these inferences (e.g., are less likely to adopt costly goal support tools following a streak, choose partners with recent streaks for joint goal pursuit). Together, these results demonstrate the significance of streaky behavior for forecasting goal adherence.

Hot streaks in the music industry: identifying and characterizing above-average success periods in artists’ careers

Hot streaks in the music industry: identifying and characterizing above-average success periods in artists’ careers

Numerical simulations on effect of cooling hole diameter on the outlet temperature distribution for a gas turbine combustor

The outlet temperature distribution characteristics of a gas turbine combustor are critical to the durability and lifetime of the turbine. Regarding to an advanced high-temperature-rise combustor, the air flow rate for swirling increases while the volume of air used to cool the wall and control the outlet temperature field decreases, causing severe challenges in effectively regulating the outlet temperature field, consequently. In the present work, with a focus on regulating the outlet temperature field under conditions of low cooling and mixed gas volume, numerical simulations of a single-sector centrally-staged combustor are carried out. The effusion cooling structure of multi-inclined cooling holes with 30° inlet angle are used on the liner wall. The impact of liner wall cooling holes with different diameters on the outlet temperature distribution characteristics is analyzed, while the variation in relative areas and distribution shapes of low-temperature regions near the outlet wall and hot streaks are obtained. The results suggest that under a constant inlet mass flow rate, both pattern factor (PF) and radial pattern factor (RPF) of the combustor increase with the increment of cooling hole diameter. Compared to the 0.5 mm hole diameter, when the diameter of each single cooling hole is doubled to 1.0 mm, the PF and RPF increase respectively by 1.14 times and 1.83 times, meanwhile, the combustion efficiency decreases from 99.97% to 97.74%, and the pressure drop reduces from 4.3% to 2.4%. Increasing the diameter of cooling holes enhances the cooling film thickness on the liner wall, resulting in the expansion of low-temperature regions near the outlet wall. Furthermore, in comparison with the smaller diameter, the larger diameter forces the combustion reaction zone to shift toward the outlet, leading to the expansion of hot streaks and a deterioration in the uniformity of the outlet temperature field. The combustor corresponding to the design scheme of multi-inclined cooling holes with 0.5 mm diameter has the most uniform outlet temperature field and the highest combustion efficiency, showing the optimum performance.

Study on coupling characteristics between multi-swirler array combustor and NGVs

A novel lean-burn burner effectively reduces NOx emissions from gas turbines, but residual swirl flow affects the NGV's performance. The multi-point array LDI combustor, as one type of lean-burn burner, lacks published articles on turbine coupling. This study conducts a comprehensive investigation of the coupling between the LDI combustor and the turbine for the first time. By analyzing the flow field characteristics using the SAS turbulence model, an innovative integrated design concept is proposed to address the challenges of combustion chamber-turbine integration. The aerodynamic and thermal characteristics of four different multi-swirler layouts are investigated. The findings indicate that compared to the conventional swirler arrangement, the multi-swirler configuration exhibits lower total pressure inhomogeneity, swirl angle, and secondary vortex intensity at the NGV. Furthermore, the multi-swirler configuration maintains the same temperature at the combustion chamber exit. The center swirler SW3 has a dominant influence on the swirler's orientation, with the endwall's thermal properties primarily affected by the clocking position. The PSW layout shows lower swirl stability and hot streaks intensity than NSW arrangement. NGV surface and exit temperature are less sensitive to the clocking position in both layouts. The PSW layout has a higher average swirl angle at the turbine inlet. The NSW arrangement has a larger fraction of momentum distribution and robust swirler stability, but hot streaks are considerable with a clear sinking consequence. A significant high temperature distribution is observed on the lower endwall and a clear thermal gradient near the exit. Both layouts show a high sensitivity of the upper endwall to clocking position. Overall, these findings provide valuable insights into the complex interactions between multi-swirler layouts and their aerodynamic and thermal characteristics, and highlight the importance of considering these factors in the design process.

The global landscape and research trend of phase separation in cancer: a bibliometric analysis and visualization.

Cancer as a deathly disease with high prevalence has impelled researchers to investigate its causative mechanisms in the search for effective therapeutics. Recently, the concept of phase separation has been introduced to biological science and extended to cancer research, which helps reveal various pathogenic processes that have not been identified before. As a process of soluble biomolecules condensed into solid-like and membraneless structures, phase separation is associated with multiple oncogenic processes. However, there are no bibliometric characteristics for these results. To provide future trends and identify new frontiers in this field, a bibliometric analysis was conducted in this study. The Web of Science Core Collection (WoSCC) was used to search for literature on phase separation in cancer from 1/1/2009 to 31/12/2022. After screening the literature, statistical analysis and visualization were carried out by the VOSviewer software (version 1.6.18) and Citespace software (Version 6.1.R6). A total of 264 publications, covering 413 organizations and 32 countries, were published in 137 journals, with an increasing trend in publication and citation numbers per year. The USA and China were the two countries with the largest number of publications, and the University of Chinese Academy of Sciences was the most active institution based on the number of articles and cooperations. Molecular Cell was the most frequent publisher with high citations and H-index. The most productive authors were Fox AH, De Oliveira GAP, and Tompa P. Overlay, whilst few authors had a strong collaboration with each other. The combined analysis of concurrent and burst keywords revealed that the future research hotspots of phase separation in cancer were related to tumor microenvironments, immunotherapy, prognosis, p53, and cell death. Phase separation-related cancer research remained in the hot streak period and exhibited a promising outlook. Although inter-agency collaboration existed, cooperation among research groups was rare, and no author dominated this field at the current stage. Investigating the interfaced effects between phase separation and tumor microenvironments on carcinoma behaviors, and constructing relevant prognoses and therapeutics such as immune infiltration-based prognosis and immunotherapy might be the next research trend in the study of phase separation and cancer.

The effects of fuel distribution on exit temperature distribution in a centrally staged combustor

Fuel injection and distribution play an important role in the formation and migration of hot streaks in gas turbine combustors and determine the exit temperature uniformity especially for modern low emission combustors that have little or no primary and dilution air flows. To better understand the underlying mechanism of the formation and evolution of hot streak, both experimental and numerical investigations have been carried out in a centrally staged tri-sector model combustor. Flow, spray, and flame have been investigated by particle image velocimetry and planar laser-induced fluorescence. The exit temperature distributions are also measured and analyzed with both laser diagnostics and simulation results. The results show that increasing fuel-to-air ratio (FAR) or fuel staging ratio enhances the formation of high temperature hot streak and leads to high overall temperature distribution factor and radial temperature distribution factor at the combustor exit. It is found that the high temperature zone is formed through the non-premixed combustion of pilot stage and resides in the shear layer of pilot stage and primary circulation zone. Increasing FAR at low power conditions and increasing SR at high power conditions promote the formation of a large hot streak area through pilot stage combustion and thus deteriorate the uniformity of temperature distribution at the combustor exit.