Modeling of cooling channel flow in liquid-propellant rocket engines

Ever since the development of liquid rocket engine, there has been a need to predict the peak heat flux that affects the engine material and thus to control the wall thermal behavior of rocket engine. To prevent thermal failure, the engine is generally cooled by means of a coolant that flows in passages that line the hottest part of the engine (i.e., combustion chamber and nozzle wall). This is the fluid-cooling system. If the coolant is one of the propellants, once it passes through the cooling circuit, it can be injected into the combustion chamber or it can be dumped overboard. The former case is referred to as Regenerative cooling system while the latter as dump cooling system. In case of high performance cryogenic rocket engine (such as LO2/hydrogen and LO2/methane engines) the coolant working pressure is supercritical and thus it behaves far from a liquid or a perfect gas. The fluid-cooling system (often referred to regenerative cooling because of the limited application of the dump cooling) of cryogenic rocket engines, is the technological background of this Ph.D. thesis. It is common and well confirmed practice in industry to analyze wall thermal behaviour of liquid rocket engine by means of simple and fast tools based on semi-empirical relationships. These relationships are generally calibrated by means of data collected in experimental tests of subscale engines. Industrial tools provide reasonable results but they are not able to accurately describe many phenomena that occur in the hot-wall/coolant environment, such as three-dimensional effects, asymmetric heat flux distribution in the material and supercritical behaviour of the coolant. For that reason, to circumvent the uncertainties of the design tools, regenerative systems are often over dimensioned. Moreover, these tools are deeply related to the engine for which they have been calibrated and thus they cannot be easily extended for a new generation of engines. In last years new approaches have risen; in fact new geometry configuration (i.e., high aspect ratio cooling channels) and new coolants (such as methane) to be used in the next future, have imposed more accurate analysis tools, such as three-dimensional Navier Stokes solver to describe coolant flow and three-dimensional Fourier analysis to describe wall thermal transmission. Simplified approaches are always used since, due to the limited computer power, three-dimensional tools are not suitable as design tools. However, accurate three-dimensional analysis can be integrated with simple and fast design tool in order to better describe and comprehend the phenomena that occur in the hot-wall/coolant environment. The aim of this study is to present and provide suitable theoretical and numerical tools able to describe the thermal behaviour that occur in regenerative cooling system, with special regard to the subcritical/supercritical coolant flow inside cooling channels. This aim has been achieved in three steps: A suitable mathematical description of thermophysical properties of coolants has been adopted. According to this mathematical modeling, computer subroutines describing the thermophysics of typical coolants (such as hydrogen and methane) have been implemented; A suitable physical and mathematical model able to describe both the wall thermal behaviour and the coolant flow that occur in regeneratively cooled rocket engines has been developed and implemented in a numerical code. The model is an extension of the typical 1D-model in the sense that it is able to describe the coolant and fin thermal stratification that occurs in high aspect ratio cooling channels. For that reason this model will be referred to as a quasi-2D model. The coolant thermophysical properties have been provided by means of the above mentioned hydrogen-methane subroutines. The code has been successfully validated with respect to the literature data; At last, a Navier-Stokes solver able to describe the high Reynolds number turbulent flow of generic fluid in three-dimensional cooling channels has been developed. This numerical tool has been successfully validated by comparison with exact solutions and literature data. Furthermore three-dimensional flow fields for a cryogenic fluid (methane) have been computed to analyze the coolant behavior inside straight channels with rectangular cross section and to discuss the channel aspect ratio effect on the cooling performances

The status of the research on the heat transfer deterioration in supercritical fluids: A review

Abstract Nowadays, both experimental and computational research on the turbulent convective heat transfer to supercritical fluids is particularly active, especially because the actual poor comprehension and prediction of the possible heat transfer deterioration is limiting the design of new promising engineering applications. In this review, such applications, among which supercritical water-cooled nuclear reactors, supercritical CO2 power generation cycles, and oxygen/methane-fuel rocket engines, are firstly introduced. Then, after a phenomenological description of the heat transfer deterioration, the status of the research is analysed in details, highlighting the major advantages and limitations of both experimental and computational studies performed so far. The review demonstrates that experimental research is mostly focused on finding simple heat transfer correlations rather than detailed models. Also detailed numerical insight of the problem is still almost unexplored. The main conclusion is that new approaches, possibly integrating extensive experiments and computations, are needed to shed new light on the problem of heat transfer to supercritical fluids

Comparative Transcriptomics Reveals Clues for Differences in Pathogenicity between Hysterothylacium aduncum, Anisakis simplex sensu stricto and Anisakis pegreffii.

Ascaridoid nematodes are widespread in marine fishes. Despite their major socioeconomic importance, mechanisms associated to the fish-borne zoonotic disease anisakiasis are still obscure. RNA-Seq and de-novo assembly were herein applied to RNA extracted from larvae and dissected pharynx of Hysterothylacium aduncum (HA), a non-pathogenic nematode. Assembled transcripts in HA were annotated and compared to the transcriptomes of the zoonotic species Anisakis simplex sensu stricto (AS) and Anisakis pegreffii (AP). Approximately 60,000,000 single-end reads were generated for HA, AS and AP. Transcripts in HA encoded for 30,254 putative peptides while AS and AP encoded for 20,574 and 20,840 putative peptides, respectively. Differential gene expression analyses yielded 471, 612 and 526 transcripts up regulated in the pharynx of HA, AS and AP. The transcriptomes of larvae and pharynx of HA were enriched in transcripts encoding collagen, peptidases, ribosomal proteins and in heat-shock motifs. Transcripts encoding proteolytic enzymes, anesthetics, inhibitors of primary hemostasis and virulence factors, anticoagulants and immunomodulatory peptides were up-regulated in AS and AP pharynx. This study represents the first transcriptomic characterization of a marine parasitic nematode commonly recovered in fish and probably of negligible concern for public health

Influence of Deposition Parameters on Hardness Properties of InconelTM 718 Processed by Laser Powder Bed Fusion for Space Applications

InconelTM 718 is widely used for commercial application in aerospace industry and additive manufacturing process allows for versatile design and manufacturing opportunities. In the present research, the results of a wide experimental campaign run on additive manufactured InconelTM 718 specimens obtained with different processing parameters are presented. In particular, the influence of process parameters (for both vertical and horizontal planes with respect to the building direction) on the hardness properties are investigated. A further investigation is performed on the optimal hardness testing procedure for additive manufacturing. The research is extended to as-built and heat-treated specimens. The new insight gained is that the orientation of the printing direction with respect to indentation direction can be responsible for scattering in hardness measurements and indentation size effect. As-built specimens show a strong anisotropy for in-plane and growth directions and an increment of hardness with respect to increasing energy density. The difference between hardness value with respect to the energy density and the measurements scattering are reduced by the heat treatment. A careful handling of hardness data is required when dealing with additive manufactured materials

Associations between depressive symptoms and disease progression in older patients with chronic kidney disease: results of the EQUAL study

Background Depressive symptoms are associated with adverse clinical outcomes in patients with end-stage kidney disease; however, few small studies have examined this association in patients with earlier phases of chronic kidney disease (CKD). We studied associations between baseline depressive symptoms and clinical outcomes in older patients with advanced CKD and examined whether these associations differed depending on sex. Methods CKD patients (>= 65 years; estimated glomerular filtration rate <= 20 mL/min/1.73 m(2)) were included from a European multicentre prospective cohort between 2012 and 2019. Depressive symptoms were measured by the five-item Mental Health Inventory (cut-off <= 70; 0-100 scale). Cox proportional hazard analysis was used to study associations between depressive symptoms and time to dialysis initiation, all-cause mortality and these outcomes combined. A joint model was used to study the association between depressive symptoms and kidney function over time. Analyses were adjusted for potential baseline confounders. Results Overall kidney function decline in 1326 patients was -0.12 mL/min/1.73 m(2)/month. A total of 515 patients showed depressive symptoms. No significant association was found between depressive symptoms and kidney function over time (P = 0.08). Unlike women, men with depressive symptoms had an increased mortality rate compared with those without symptoms [adjusted hazard ratio 1.41 (95% confidence interval 1.03-1.93)]. Depressive symptoms were not significantly associated with a higher hazard of dialysis initiation, or with the combined outcome (i.e. dialysis initiation and all-cause mortality). Conclusions There was no significant association between depressive symptoms at baseline and decline in kidney function over time in older patients with advanced CKD. Depressive symptoms at baseline were associated with a higher mortality rate in men

A CFD-derived correlation for methane heat transfer deterioration

Methane heat-transfer deterioration can occur in the regenerative cooling channels of future liquid-oxygen/liquid-methane rocket engines with chamber pressures higher than about 50 bar. Aiming to improve the prediction capabilities for the design of such systems, in the present study, a Nusselt number correlation able to describe the convective heat-transfer characteristics of supercritical flow exhibiting deterioration and with negligible buoyancy effects is obtained using data from numerical simulations. The adopted numerical solver of the Navier–Stokes equations is first validated against the experimental data of near-critical hydrogen in heated tubes and then used to collect heat-transfer data of supercritical methane in a heated tube for different levels of pressure, temperature, and mass flux

Dataset of the experimentally measured heat transfer in the throat region of liquid rocket engine thrust chambers

About 500 experimental heat transfer data taken from the open literature and relevant to the most thermally solicited area (i.e., the throat region) of liquid rocket engine thrust chambers, are collected and manipulated. This collection is the outcome of a thorough and exhaustive survey of the available experimental data of hot-fire tests produced to date. Among the test cases reported in the literature, only those with a throat heat transfer that is not affected by laminar flow, evident soot deposition, or intended non-uniform propellant injection are collected. The heat transfer is typically measured in terms of wall heat flux and temperature. Sometimes the heat transfer coefficient, which is a combination of these two terms, is provided. Each collected heat transfer measurement is supplied with data relevant to the specific operative condition of the considered test case, as well as the configuration of the adopted thrust chamber and propellant injector. Among the different considered propellant combinations, most of the experiments are made burning oxygen-hydrogen or oxygen-kerosene. Experiments made using mildly heated and compressed air, although not a rocket propellant, are also considered because of their relevance to the problem of interest. The collected dataset, called the primary dataset, is numerically elaborated to create a secondary dataset that is more thorough and consistent than the primary one. In fact, also thanks to the adoption of a suitable hot-gas flow modeling, the secondary dataset contains elaborated data that are not always available in the selected open-literature as well as the non-dimensional numbers that are associated with the heat transfer and are typically used in regression rules, like the Nusselt and the Stanton numbers. The datasets presented in this manuscript are discussed and used to find heat transfer regressions in the research manuscript “Overview and analysis of the experimentally measured throat heat transfer in liquid rocket engine thrust chambers”, Acta Astronaut. 184 (2021), 46-58 [1]

Effectiveness of the Spalart-Allmaras Turbulence Model in the Analysis of Curved Rocket Engine Cooling Channels

In this study, the standard and the modified Spalart-Allmaras one-equation turbulence models are implemented in a numerical solver to assess their effectiveness in describing the coolant flow in curved rocket engine cooling channels. Comparison with published experimental data has demonstrated that, in the case of curvature, the modified turbulence model improves the prediction of the skin friction but not of the heat transfer with respect to the standard one. Then, the analysis of two sample test cases inspired by the cooling circuit of the space shuttle main engine have shown that the standard Spalart-Allmaras turbulence model can be profitably used to describe the coolant flowfield and heat transfer

Finite-Volume Solver of the Euler Equation for Real Fluids

The analysis of real-fluid flow have a particular importance for the description of many technological devices that operates with compressible fluids that cannot be described either as perfect gas or as incompressible fluid, such as regenerative cooling system for cryogenic rocket engine. The aim of this study is to introduce the problem of real fluid-dynamics by means of the unsteady one-dimensional Euler equation for a generic, single-phase, compressible fluid. A proper numerical solver based on a finite-volume, Godunov-type approach, which is second order accurate in space, is presented. Three different approximate Riemann solvers, which are the crucial point of the Godunov-type schemes, are extended for the case of real fluids. Finally, the accuracy and robustness of the numerical solver are proved on shock-tube experiments for methane in gas, vapor, liquid and supercritical state. Fluid properties are described by means of the high accuracy MBWR equation of state

Analysis of thermal stratification impact on the design of cooling channels for liquid rocket engines

The choice of the shape and number of cooling channels is critical when seeking for the best design of a liquid rocket engine thrust chamber. Trade-off has to be considered among the different constraints that must be satisfied in terms of thrust chamber mass and resistance to mechanical and thermal loads, while keeping acceptable the power spent to make the coolant flow in the channels. In this study attention is focused on the phenomenon of thermal stratification that occurs in liquid rocket engine cooling channels due to their asymmetric heating. Its role is studied with a suitable engineering approach that allows to emphasize when rectangular cross section channels become inefficient due to stratification. A parametric analysis is carried out on a reference configuration showing the margins required to satisfy specific wall temperature constraints