•Developed a new FSI method for compliant thin structures involving large deformations.•Coupling of an IIM for compressible flows with a geometrically nonlinear FEM solver.•Developed FEM solver with ...geometrically nonlinear, ‘locking free’ thin shell elements.•Addresses the algorithmic challenges for parallelizing a partitioned FSI method.•Simulating the inflation of a spacecraft disk-gap-band parachute in supersonic flow.
A parallel computational method for simulating fluid–structure interaction problems involving large, geometrically nonlinear deformations of thin shell structures is presented and validated. A compressible Navier-Stokes solver utilizing a higher-order finite difference immersed boundary method is coupled with a geometrically nonlinear computational structural dynamics solver employing the mixed interpolation of tensorial components formulation for thin triangular shell elements. A weak fluid–structure coupling strategy is used to advance the numerical solution in time. The thin shell structures are represented in the fluid domain by a geometry mesh with a finite thickness at or below the size of the local grid spacing in the fluid domain. The methodologies for load and displacement transfer between the disparate geometry and structural meshes are detailed considering a parallel computing environment. The coupled method is validated for canonical simulation-based test cases and experimental fluid–structure interaction problems considering large deformations of thin shell structures, including a shock impinging on a cantilever plate, a fixed cylinder with a flexible trailing filament in channel flow, a thin, clamped plate in wall-bounded flow, and a flag waving in viscous crossflow. The FSI method is then demonstrated on a compliant circular sheet with a clamped center exposed to crossflow and finally applied to the inflation of a spacecraft disk-gap-band parachute inflating in supersonic flow conditions resembling the upper Martian atmosphere, where comparison with experimental data is provided.
•Novel positivity-preserving limiters for high-order methods are developed for compressible gas-liquid flows.•The interpolation and flux limiters ensure bounded volume fractions and positive ...densities and squared sound speed.•The positivity-preserving properties of the HLLC flux for the five-equation model by Allaire et al. are shown.•The flux limiting on any high-order flux is discretely conservative for all conservative equations of the flow model.•The fifth order incremental-stencil WCNS with the limiters is shown to be robust with intense problems.
We present a robust, highly accurate, and efficient positivity- and boundedness-preserving diffuse interface method for the simulations of compressible gas-liquid two-phase flows with the five-equation model by Allaire et al. using high-order finite difference weighted compact nonlinear scheme (WCNS) in the explicit form. The equation of states of gas and liquid are given by the ideal gas and stiffened gas laws respectively. Under a mild assumption on the relative magnitude between the ratios of specific heats of the gas and liquid, we can construct limiting procedures for the fifth order incremental-stencil WCNS (WCNS-IS) with the first order Harten–Lax–van Leer contact (HLLC) flux such that positive partial densities and squared speed of sound can be ensured in the solutions, together with bounded volume fractions and mass fractions. The limiting procedures are discretely conservative for all conservative equations in the five-equation model and can also be easily applied to any other conservative finite difference or finite volume scheme. Numerical tests with liquid water and air are reported to demonstrate the robustness and high accuracy of the WCNS-IS with the positivity- and boundedness-preserving limiters even under extreme conditions.
Noise generation mechanisms for a perfectly expanded supersonic Mach number
$M=1.8$
turbulent jet impinging on a
$45^{\circ }$
inclined plate are investigated for a Reynolds number of
$1.6\times ...10^{6}$
employing a large-eddy simulation. Excellent comparisons with experimental acoustic far-field measurements and pressure measurements on the impingement plate are obtained. Two local maxima are identified in the far-field overall sound pressure levels in the
$75^{\circ }$
and
$120^{\circ }$
observer directions, which are associated with different noise generation mechanisms. The peak frequencies in the spectra with Strouhal numbers of
$St=0.2$
for
$75^{\circ }$
and
$St=0.5$
for
$120^{\circ }$
match the experimental measurements. The jet-impingement region generates pressure waves that propagate predominantly in the
$120^{\circ }$
observer direction. The noise generation in this region is attributed to vortex stretching and tearing during shear-layer impingement, and shock oscillations that are induced by the motion of downstream convected vortical flow structures. The second peak in the overall sound pressure distribution at
$75^{\circ }$
is associated with noise sources located in the wall jet. The noise generation in the wall jet is associated with supersonically convecting large-scale coherent flow structures that also interact with tail shocks in the wall jet causing large localized pressure fluctuations. Strongly coherent flow structures are identified by applying proper orthogonal decomposition (POD) to the unsteady flow field. The frequency characteristics of the most energetic POD modes are distinctly different based on which energy norm is chosen. The most energetic entropy-based POD modes contain a peak frequency of approximately
$St=0.4{-}0.6$
, while the most energetic turbulent kinetic-energy-based POD modes appear to be dominated by lower-frequency content. The causality method, based on Lighthill’s acoustic analogy, is used to link the acoustic noise signature to the relevant physical mechanisms in the source region. A differentiation is made between the application of normalized and non-normalized cross-correlation functions for noise source identification and characterization.
•Pure and W-doped ZnO films were synthesized using sputtering at 0.4Pa and 1.33Pa.•The doped film deposited at 1.33Pa has shown spiky morphology with much lower grain density and porosity than the ...film deposited at 0.4Pa.•This film deposited at 1.33Pa favoured the formation of active site for OH adsorption and found not suitable for gas sensing.•A higher oxidation state of W (35.9eV) was found in the W-doped ZnO film deposited at 0.4Pa.•This film deposited at 0.4Pa has shown greater gas sensing to NO2 at lower operating temperature most likely due to enhanced free-carrier defects.
Pure and W-doped ZnO thin films were obtained using magnetron sputtering at working pressures of 0.4Pa and 1.33Pa. The films were deposited on glass and alumina substrates at room temperature and subsequently annealed at 400°C for 1h in air. The effects of pressure and W-doping on the structure, chemical, optical and electronic properties of the ZnO films for gas sensing were examined. From AFM, the doped film deposited at higher pressure (1.33Pa) has spiky morphology with much lower grain density and porosity compared to the doped film deposited at 0.4Pa. The average gain size and roughness of the annealed films were estimated to be 65nm and 2.2nm, respectively with slightly larger grain size and roughness appeared in the doped films. From XPS the films deposited at 1.33Pa favoured the formation of adsorbed oxygen on the film surface and this has been more pronounced in the doped film which created active sites for OH adsorption. As a consequence the W-doped film deposited at 1.33Pa was found to have lower oxidation state of W (35.1eV) than the doped film deposited at 0.4Pa (35.9eV). Raman spectra indicated that doping modified the properties of the ZnO film and induced free-carrier defects. The transmittance of the samples also reveals an enhanced free-carrier density in the W-doped films. The refractive index of the pure film was also found to increase from 1.7 to 2.2 after W-doping whereas the optical band gap only slightly increased. The W-doped ZnO film deposited at 0.4Pa appeared to have favourable properties for enhanced gas sensing. This film showed significantly higher sensing performance towards 5–10ppm NO2 at lower operating temperature of 150°C most dominantly due to increased free-carrier defects achieved by W-doping.
•Comparison of three most common classes of higher-order finite difference shock capturing schemes.•Truncation error and spectral resolution analysis of the underlying optimal schemes.•Wide range of ...test cases were used to study key aspects of higher-order schemes.•Detailed cost breakdown of each individual scheme.•Comparison of the overall cost and efficiency of the different schemes.
The efficiency of computational fluid dynamics simulations can be greatly enhanced by employing higher-order accurate numerical schemes which provide superior accuracy for a given cost. For unsteady turbulent flow simulations involving shocks, contacts, and/or material discontinuities, various higher-order shock capturing schemes are available in the literature. The desired numerical scheme should be free of spurious numerical oscillations across discontinuities and it should obtain higher-order accuracy in smooth flow regions in an efficient manner. Sufficient robustness is necessary for effectively utilizing these numerical methods in engineering and science applications. Three classes of higher-order shock capturing schemes are compared in this paper: (1) central finite-difference schemes with explicit artificial dissipation, (2) a compact centered finite-difference scheme with localized artificial diffusivity and (3) weighted essentially non-oscillatory schemes in both explicit and compact finite difference forms. Multiple variations of these methods were implemented and tested using a block-structured Cartesian mesh solver. The current paper assesses shock capturing capabilities as well as effects on the accuracy in smooth flow regions using a variety of test cases that range from canonical shock problems to homogeneous isotropic turbulence at a turbulent Mach number of 0.5 where shocklets are formed. Finally, a computational cost breakdown for each scheme is provided and the overall computational efficiency of the different schemes are compared to each other.
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