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Research Papers

A Materials Selection Protocol for Lightweight Actively Cooled Panels

[+] Author and Article Information
Lorenzo Valdevit

Mechanical and Aerospace Engineering Department, University of California, Irvine, CA 92697-3975

Natasha Vermaak, Frank W. Zok, Anthony G. Evans

Materials Department, University of California, Santa Barbara, CA 93106-5050

The horizontal resistance is not properly conductive, as convection occurs along one of the sides. FE calculations reveal that using an effective length equal to half the actual length yields accurate results (hence the factor of 4).

J. Appl. Mech 75(6), 061022 (Aug 22, 2008) (15 pages) doi:10.1115/1.2966270 History: Received February 24, 2008; Revised June 06, 2008; Published August 22, 2008

This article provides a materials selection methodology applicable to lightweight actively cooled panels, particularly suitable for the most demanding aerospace applications. The key ingredient is the development of a code that can be used to establish the capabilities and deficiencies of existing panel designs and direct the development of advanced materials. The code is illustrated for a fuel-cooled combustor liner of a hypersonic vehicle, optimized for minimum weight subject to four primary design constraints (on stress, temperatures, and pressure drop). Failure maps are presented for a number of candidate high-temperature metallic alloys and ceramic composites, allowing direct comparison of their thermostructural performance. Results for a Mach 7 vehicle under steady-state flight conditions and stoichiometric fuel combustion reveal that, while C–SiC satisfies the design requirements at minimum weight, the Nb alloy Cb752 and the Ni alloy Inconel X-750 are also viable candidates, albeit at about twice the weight. Under the most severe heat loads (arising from heat spikes in the combustor), only Cb752 remains viable. This result, combined with robustness benefits and fabrication facility, emphasizes the potential of this alloy for scramjets.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Artist rendition of a prototypical hypersonic air-breathing vehicle. (b) Schematic of actively cooled panel with thermostructural loads.

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Figure 2

Schematic of the materials selection procedure

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Figure 3

(a) Thermal resistance network used to determine temperature distributions, along with expressions for all relevant thermal resistances. (b) Effective network.

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Figure 4

Distribution of the heat transfer coefficient in the cooling channel extracted from the CFD simulation of a near-optimal Inconel X-750 panel. (a) Variation of pointwise hC around channel perimeter at z∕Z=0.9. (b) Variation of cross-section averaged hC along the axial direction. The value extracted from the Gnielinski correlation (Eq. 1) and used in the analytical model is depicted for comparison.

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Figure 5

Comparison of analytical and numerical (FE) temperature distributions for an optimal Inconel X-750 panel. All temperatures are in Kelvin. Values in parentheses are analytical predictions. Both the maximum temperature in the structure and the temperature differences that drive the thermal stresses are captured accurately.

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Figure 6

Mechanical boundary conditions. [(a) and (b)] Linear rollers on two sides (Type I). (b) Multiple linear rollers with regular spacing. (c) Uniform two-dimensional bed of rollers, with impeded rotation at the ends (Type II). (d) Benchmark boundary condition: plate sitting on rigid foundation (inset). The chart compares the temperature increase from room temperature to the material upper use limit needed to cause yielding. Under this boundary condition, the full high-temperature potential of the materials is not exploited.

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Figure 7

Unit cells susceptible to local yielding and the 18 critical points

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Figure 8

Comparison of analytical and numerical (FE) von Mises stress distributions for an optimal Inconel X-750 panel. The plots show the results for thermal, mechanical, and combined thermomechanical stresses along the four paths. With the exception of Points 2 and 3, clearly affected by stress intensification, the agreement is satisfactory, particularly on the top face, where the highest stresses generally occur.

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Figure 9

Design maps for several materials considered in this study, with and without a TBC. The normalizing parameters for the equivalence ratio (ϕ=f∕fst) and the heat transfer coefficient (hG∕hGnom) are those expected for steady-state Mach 7 flight conditions.

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Figure 10

Minimum weight comparison at two levels of heat transfer: (a) and (b) hG=445 and (c) and (d) 890W∕m2K. [(a) and (c)] the solid lines represent the results for uncoated materials whereas [(b) and (d)] the dashed lines are those for TBC coated materials.

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Figure 11

Constraint activity map for Cb752 for hG values of (a) 445W∕m2K and (b) 890W∕m2K. Constraint is active when its activity parameter reaches unity. At the lower thermal load, only the therm-omechanical constraints are active (yielding under mechanical and combined loads). When the thermal load is doubled, at low flow rates, both the solid and fuel temperatures approach their maximum allowable value.

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