Cooling Channel Wall Research Articles

3D fluid–structure interaction analysis of a typical liquid rocket engine cycle based on a novel viscoplastic damage model

SUMMARYIn many space missions, expandable or reusable launch systems are used. In this context, the reliable design of liquid rocket engines (LREs) is a key issue. In the present paper, we present a novel combination of numerical schemes. It is applied to model the extreme physical phenomena a typical LRE undergoes during its loading cycles. The numerical scheme includes a partitioned fluid–structure interaction (FSI) algorithm in combination with a unified viscoplastic damage model. This allows the complex description of the material response under cyclic thermomechanical loading taking place in LREs. In this regard, we focus on the response of the cooling channel wall that is made from copper alloys. For the coupled FSI analysis, the individual domains of the rocket thrust chamber are modeled by a 3D parametrized approach. The well‐established single field solver codes, DLR TAU for the hot gas and ABAQUS FE software for the structural domain, are coupled via the inhouse developed simulation environment ifls. Ifls provides the necessary algorithms for a partitioned coupling approach such as individual code steering, data interpolation, time integration and iteration control. Finally, the results of an FSI analysis of a complete engine cycle are presented. They show the potential of the new numerical scheme for the lifetime prediction of LREs.Copyright © 2013 John Wiley & Sons, Ltd.

Studies on Rheocasting Using Cooling Slope

In the present work, a cooling channel is employed to produce semi-solid A356 alloy slurry. To understand the transport process involved, a 3D non-isothermal, multiphase volume averaging model has been developed for simulation of the semi-solid slurry generation process in the cooling channel. For simulation purpose, the three phases considered are the parent melt, the nearly spherical grains and air as separated but highly coupled interpenetrating continua. The conservation equations of mass, momentum, energy and species have been solved for each phase and the thermal and mechanical interactions (drag force) among the phases have been considered using appropriate model. The superheated liquid alloy is poured at the top of the cooling slope/channel, where specified velocity inlet boundary condition is used in the model, and allowed to flow along gravity through the channel. The melt loses its superheat and becomes semisolid up to the end of cooling channel due to the evolving -Al grains with decreasing temperature. The air phase forms a definable air/liquid melt interface, i.e. free surface, due its low density. The results obtained from the present model includes volume fractions of three different phases considered, grain evolution, grain growth rate, size and distribution of solid grains. The effect of key process variables such as pouring temperature, slope angle of the cooling channel and cooling channel wall temperature on temperature distribution, velocity distribution, grain formation and volume fraction of different phases are also studied. The results obtained from the simulations are validated by microstructure study using SEM and quantitative image analysis of the semi-solid slurry microstructure obtained from the experimental set-up.

Solution of the inverse heat conduction problem described by the Poisson equation for a cooled gas-turbine blade

The presented paper describes a method of solving the inverse problems of heat conduction, consisting in solving the Poisson equation for a simply connected region instead of the Laplace equation for a multiply connected one, like a gas-turbine blade provided with cooling channels. The considered method consists in determining unknown values of the source (heat sink) power in the cooling channels for a given external heat transfer situation to achieve as close as possible an isothermal outer surface. Afterwards the temperature and heat flux distributions at the cooling channel walls are determined. Since the unknown source power is sought, the problem is an inverse one. Taking into account the sought values the method is reckoned among the class of the fictitious source methods and presents an optimization scheme. Using an exemplary gas turbine blade cooling configuration, the results of the calculation obtained with this method have been compared to the results achieved with an inverse method using the boundary element method for a multiple connected region.The results obtained with both methods within the optimization scheme approximated each other. Nevertheless, the results for the inverse method shown in the present paper gave nearly no oscillations, which is important in case of the blades with other geometric features of the cooling channels.

A Viscoplastic‐Damage Model for the Lifetime Prediction of Regeneratively Cooled Noozle Structures

AbstractThe cooling channel wall within the combustion chamber of a Reusable Launch Vehicle (RLV) is subjected to severe operating conditions which eventually lead to the damage of the wall. The failure mode is well known as the “dog‐house” effect where the wall becomes thinner and bulges toward the interior of the chamber. Supported by the German Research Foundation, a viscoplastic‐damage model is being developed to enable a realistic description of the material behaviour under extreme cyclic thermomechanical loadings where creep and hardening phenomena might take place. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

C13 Finishing of Inner Wall of Cooling Channel in Mold by High Speed Flowing(Abrasive finishing technology)

Recently, a multifunction machine, in which a ferrous based powder bed is selectively heated and fused by a laser beam irradiation and the edge of consolidated structure obtained is cut with end mill, has been developed to produce an injection molding die. In this device, complicated shapes of the injection molding die is obtained without dividing into each block for locating the cooling channels. However, there have been the problems to be solved about the surface conditions of the inner wall located as cooling channels. This paper deals with a new polishing process of inner wall with flowing slurry at high performance. In order to investigate the influence of various conditions on the polishing of the inner wall, the effects of grain size and polishing time on the surface roughness are evaluated experimentally. The process enables to obtain the inner wall without partially melted powder and unmelted powder.

Thermo-Mechanical Analysis of RLV Thrust Cell Liners with Homogeneous and Graded Coatings

The Higher-Order Theory for Cylindrical Functionally Graded Materials is employed to investigate the effectiveness of thermal barrier coatings in mitigating deformation mechanisms in thrust cell liners leading to experimentally observed failure modes. The results indicate that under the employed thermo-mechanical loading histories coating thickness has a great impact on temperature and deformation fields within the cooling channel wall of a thrust cell liner, with thicker coatings producing more desirable temperature and deformation fields. Functional grading of metallic substrate and coating materials does not produce improvement in terms of overall thrust cell liner performance. Further, the application of grading is potentially detrimental due to likely roughening of the thrust cell liner wall in the combustion chamber as a result of local deformations around relatively coarse inclusions. The homogenized approach to analyzing the graded coating effectiveness is incapable of capturing these localized effects, leading to erroneous conclusions.

Role of the Material Constitutive Model in Simulating the Reusable Launch Vehicle Thrust Cell Liner Response

The reusable launch vehicle thrust cell liner, or thrust chamber, is a critical component of the space shuttle main engine. It is designed to operate in some of the most severe conditions seen in engineering practice. These conditions give rise to characteristic deformations of the cooling channel wall exposed to high thermal gradients and a coolant-induced pressure differential, characterized by the wall’s bulging and thinning, which ultimately lead to experimentally observed “dog-house” failure modes. In this paper, these deformations are modeled using the cylindrical version of the higher-order theory for functionally graded materials in conjunction with two inelastic constitutive models for the liner’s constituents, namely Robinson’s unified viscoplasticity theory and the power-law creep model. Comparison of the results based on these two constitutive models under cyclic thermomechanical loading demonstrates that, for the employed constitutive model parameters, the power-law creep model predicts more ...

Gas-cooled high performance divertor for a power plant

Designing divertor target plates for a fusion power plant is a challenging task because they have to allow exceptionally high heat fluxes, deliver heat to the power conversion system at a temperature suitable for high efficiency, and use a coolant compatible with the blanket system. These requirements are different from the case of an experimental reactor (e.g. ITER) where copper can be used as heat sink. In a power plant, the use of cold water as divertor coolant would waste 10–20% of the total power, with a comparable reduction of thermal efficiency. This paper proposes a helium cooled divertor concept that is intended to reach 10 MW/m 2 peak surface heat flux. The evolution of the design, by strictly applying high heat flux criteria to an existing porous medium concept, is presented. Enhanced heat transfer is achieved by a pin fin array on the cooling channel wall. An operating point is selected, and finite element analyses performed to establish temperature and stress levels in a divertor target plate. Results indicate that the design meets the requirements.

Study of the velocity distribution in an intense pulsed hydrogen beam

We present the results of measurements of the velocity distributions of particles in a pulsed hydrogen beam obtained from a dissociator with a radio frequency discharge (duration 1.0 ms, repetition rate 1 Hz). It is shown that the hydrogen inside the dissociator is heated up to ∼2800 K, so the thermal dissociation of hydrogen molecules is essential. In order to cool the atoms, the gas was let through a pyrex channel 5 mm in diameter. The cooling channel walls being at room temperature and the channel having a length of 50 mm, we have obtained a supersonic beam of hydrogen atoms with a Mach number M | = 2.7±0.25. When the channel walls were cooled by the flowing liquid nitrogen and the channel was 70 mm long we obtained a beam of cooled atoms with a Mach number M | = 4.14±0.35. The velocity distribution of atoms depends on the power of the rf discharge inside the dissociator and on the gas consumption per pulse, and varies during the discharge pulse. For a temperature of the cooling channel walls T ch = 77 K, a gas consumption N = 3.3×10 17 molecules per pulse and a discharge power of 0.23 kW cm −3, we have obtained an atomic beam with intensity I(0) = (2.8±0.8)×10 20 atoms sr −1 s −1 and a most probable velocity ν MP = (1.97±0.07)×10 5 cm s −1.