A Numerical Study of Shock and Heating With Rarefaction for Hypersonic Flow Over a Cylinder

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Ashwani Assam ◽  
M. R. Nived ◽  
Nikhil Narayan Kalkote ◽  
Vinayak Eswaran
Keyword(s):  
Heat Flux ◽  
Numerical Study ◽  
Hypersonic Flows ◽  
Flow Properties ◽  
Aerospace Vehicles ◽  
Heating Value ◽  
Carbuncle Phenomenon ◽  
Blunt Bodies ◽  
Convective Scheme ◽  
The Continuum

Abstract The numerical computation of hypersonic flows over blunt bodies is challenging due to the difficulty in robust and accurate wall heat flux prediction and proper capturing of shock waves free from the “carbuncle” phenomenon and other shock anomalies. It is important to understand how this behavior is affected due to rarefaction, which in turn will help to improve the study of aerospace vehicles flowing in rarefied and hypersonic regime. Recently, the SLAU2 convective scheme was shown to suppress the shock anomalies found in capturing strong shocks, however, it still showed a wavy pattern of heating. We have proposed a modification to the SLAU2 convective scheme to improve the accuracy of flow predictions in the presence of strong shocks. We then perform the numerical simulation of hypersonic viscous flow over a cylinder at Mach 8 and 16.34 at different Knudsen numbers. We carry out the study using the modified SLAU2 and the classical Roe schemes. We study how the shock anomalies found in the continuum hypersonic flows behave with the degree of rarefaction. It is found that the modified SLAU2 captures the shock free from the shock anomalies at all Kn, while the Roe scheme lacks robustness for Kn≲10−3. The variation of different flow properties such as heat flux, wall shear stress, and the Mach number is investigated. The peak heating value was observed to decrease with the degree of rarefaction.

scholarly journals Experimental and Numerical Study of a Microcogeneration Stirling Unit under On–Off Cycling Operation

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 801
Author(s):  
Gianluca Valenti ◽  
Aldo Bischi ◽  
Stefano Campanari ◽  
Paolo Silva ◽  
Antonino Ravidà ◽  
...  
Keyword(s):  
Numerical Study ◽  
Thermal Storage ◽  
Primary Energy ◽  
Operational Cost ◽  
Cogeneration Plant ◽  
Economic Optimization ◽  
Viable Option ◽  
Heating Value ◽  
Energy Flows

Stirling units are a viable option for micro-cogeneration applications, but they operate often with multiple daily startups and shutdowns due to the variability of load profiles. This work focused on the experimental and numerical study of a small-size commercial Stirling unit when subjected to cycling operations. First, experimental data about energy flows and emissions were collected during on–off operations. Second, these data were utilized to tune an in-house code for the economic optimization of cogeneration plant scheduling. Lastly, the tuned code was applied to a case study of a residential flat in Northern Italy during a typical winter day to investigate the optimal scheduling of the Stirling unit equipped with a thermal storage tank of diverse sizes. Experimentally, the Stirling unit showed an integrated electric efficiency of 8.9% (8.0%) and thermal efficiency of 91.0% (82.2%), referred to as the fuel lower and, between parenthesis, higher heating value during the on–off cycling test, while emissions showed peaks in NOx and CO up to 100 ppm but shorter than a minute. Numerically, predictions indicated that considering the on–off effects, the optimized operating strategy led to a great reduction of daily startups, with a number lower than 10 per day due to an optimal thermal storage size of 4 kWh. Ultimately, the primary energy saving was 12% and the daily operational cost was 2.9 €/day.

scholarly journals Pool Boiling of Nanofluids on Biphilic Surfaces: An Experimental and Numerical Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 125
Author(s):  
Eduardo Freitas ◽  
Pedro Pontes ◽  
Ricardo Cautela ◽  
Vaibhav Bahadur ◽  
João Miranda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Pool Boiling ◽  
Temperature Drop ◽  
Surface Cooling ◽  
Average Temperature ◽  
Gold Silver

This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool-boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions were developed and used as surface interfaces with different nanofluids (water with gold, silver, aluminum and alumina nanoparticles), in order to evaluate the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. To study the nucleation of a single bubble in pool boiling condition, a numerical model was also implemented. The results show an evident benefit of using biphilic patterns with well-established distances between the superhydrophobic regions. This can be observed in the resulting plot of the dissipated heat flux for a biphilic pattern with seven superhydrophobic spots, δ = 1/d and an imposed heat flux of 2132 w/m2. In this case, the dissipated heat flux is almost constant (except in the instant t* ≈ 0.9 when it reaches a peak of 2400 W/m2), whilst when using only a single superhydrophobic spot, where the heat flux dissipation reaches the maximum shortly after the detachment of the bubble, dropping continuously until a new necking phase starts. The biphilic patterns also allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic spacing between the superhydrophobic regions, which clearly contributes to cool down the surface. This effect is noticeable in the case of employing the Ag 1 wt% nanofluid, with an imposed heat flux of 2132 W/m2, where the coalescence of the drops promotes a surface cooling, identified by a temperature drop of 0.7 °C in the hydrophilic areas. Those areas have an average temperature of 101.8 °C, whilst the average temperature of the superhydrophobic spots at coalescence time is of 102.9 °C. For low concentrations as the ones used in this work, the effect of the nanofluids was observed to play a minor role. This can be observed on the slight discrepancy of the heat dissipation decay that occurred in the necking stage of the bubbles for nanofluids with the same kind of nanoparticles and different concentration. For the Au 0.1 wt% nanofluid, a heat dissipation decay of 350 W/m2 was reported, whilst for the Au 0.5 wt% nanofluid, the same decay was only of 280 W/m2. The results of the numerical model concerning velocity fields indicated a sudden acceleration at the bubble detachment, as can be qualitatively analyzed in the thermographic images obtained in this work. Additionally, the temperature fields of the analyzed region present the same tendency as the experimental results.

Numerical study of self-avoiding walks on lattices and in the continuum

1991 ◽  
Vol 24 (7) ◽  
pp. 1615-1621 ◽  
Author(s):  
A. J. Barrett ◽  
Marc Mansfield ◽  
Brad C. Benesch
Keyword(s):  
Numerical Study ◽  
Self Avoiding Walks ◽  
The Continuum

Oscillatory Heat Transfer in a Pipe Subjected to a Laminar Reciprocating Flow

1996 ◽  
Vol 118 (3) ◽  
pp. 592-597 ◽  
Author(s):  
T. S. Zhao ◽  
P. Cheng
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Nusselt Number ◽  
Numerical Study ◽  
Temperature Cycle ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Cycle Space ◽  
Reciprocating Flow

An experimental and numerical study has been carried out for laminar forced convection in a long pipe heated by uniform heat flux and subjected to a reciprocating flow of air. Transient fluid temperature variations in the two mixing chambers connected to both ends of the heated section were measured. These measurements were used as the thermal boundary conditions for the numerical simulation of the hydrodynamically and thermally developing reciprocating flow in the heated pipe. The coupled governing equations for time-dependent convective heat transfer in the fluid flow and conduction in the wall of the heated tube were solved numerically. The numerical results for time-resolved centerline fuid temperature, cycle-averaged wall temperature, and the space-cycle averaged Nusselt number are shown to be in good agreement with the experimental data. Based on the experimental data, a correlation equation is obtained for the cycle-space averaged Nusselt number in terms of appropriate dimensionless parameters for a laminar reciprocating flow of air in a long pipe with constant heat flux.

Numerical study of the flow of R1270‐based nanorefrigerants in a circular tube subject to uniform heat flux

2018 ◽  
Vol 13 (12) ◽  
pp. 1693-1698 ◽  
Author(s):  
Mohammed Zohud ◽  
Ahmed Ouadha ◽  
Redouane Benzeguir
Keyword(s):  
Heat Flux ◽  
Circular Tube ◽  
Numerical Study ◽  
Uniform Heat Flux ◽  
Uniform Heat

scholarly journals Seasonal Surface Air Temperature and Precipitation in the FSU Climate Model Coupled to the CLM2

2005 ◽  
Vol 18 (16) ◽  
pp. 3217-3228 ◽  
Author(s):  
D. W. Shin ◽  
S. Cocke ◽  
T. E. LaRow ◽  
James J. O’Brien
Keyword(s):  
Heat Flux ◽  
Air Temperature ◽  
Climate Model ◽  
Initial Conditions ◽  
Sensible Heat Flux ◽  
Surface Air Temperature ◽  
Community Land Model ◽  
Temperature And Precipitation ◽  
The Impact ◽  
Convective Scheme

Abstract The current Florida State University (FSU) climate model is upgraded by coupling the National Center for Atmospheric Research (NCAR) Community Land Model Version 2 (CLM2) as its land component in order to make a better simulation of surface air temperature and precipitation on the seasonal time scale, which is important for crop model application. Climatological and seasonal simulations with the FSU climate model coupled to the CLM2 (hereafter FSUCLM) are compared to those of the control (the FSU model with the original simple land surface treatment). The current version of the FSU model is known to have a cold bias in the temperature field and a wet bias in precipitation. The implementation of FSUCLM has reduced or eliminated this bias due to reduced latent heat flux and increased sensible heat flux. The role of the land model in seasonal simulations is shown to be more important during summertime than wintertime. An additional experiment that assimilates atmospheric forcings produces improved land-model initial conditions, which in turn reduces the biases further. The impact of various deep convective parameterizations is examined as well to further assess model performance. The land scheme plays a more important role than the convective scheme in simulations of surface air temperature. However, each convective scheme shows its own advantage over different geophysical locations in precipitation simulations.

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