Commenced in January 2007
Frequency: Monthly
Edition: International
Paper Count: 3

Search results for: forebody

3 Surface Pressure Distributions for a Forebody Using Pressure Sensitive Paint

Authors: Yi-Xuan Huang, Kung-Ming Chung, Ping-Han Chung

Abstract:

Pressure sensitive paint (PSP), which relies on the oxygen quenching of a luminescent molecule, is an optical technique used in wind-tunnel models. A full-field pressure pattern with low aerodynamic interference can be obtained, and it is becoming an alternative to pressure measurements using pressure taps. In this study, a polymer-ceramic PSP was used, using toluene as a solvent. The porous particle and polymer were silica gel (SiO₂) and RTV-118 (3g:7g), respectively. The compound was sprayed onto the model surface using a spray gun. The absorption and emission spectra for Ru(dpp) as a luminophore were respectively 441-467 nm and 597 nm. A Revox SLG-55 light source with a short-pass filter (550 nm) and a 14-bit CCD camera with a long-pass (600 nm) filter were used to illuminate PSP and to capture images. This study determines surface pressure patterns for a forebody of an AGARD B model in a compressible flow. Since there is no experimental data for surface pressure distributions available, numerical simulation is conducted using ANSYS Fluent. The lift and drag coefficients are calculated and in comparison with the data in the open literature. The experiments were conducted using a transonic wind tunnel at the Aerospace Science and Research Center, National Cheng Kung University. The freestream Mach numbers were 0.83, and the angle of attack ranged from -4 to 8 degree. Deviation between PSP and numerical simulation is within 5%. However, the effect of the setup of the light source should be taken into account to address the relative error.

Keywords: pressure sensitive paint, forebody, surface pressure, compressible flow

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2 Hydrodynamics Study on Planing Hull with and without Step Using Numerical Solution

Authors: Koe Han Beng, Khoo Boo Cheong

Abstract:

The rising interest of stepped hull design has been led by the demand of more efficient high-speed boat. At the same time, the need of accurate prediction method for stepped planing hull is getting more important. By understanding the flow at high Froude number is the key in designing a practical step hull, the study surrounding stepped hull has been done mainly in the towing tank which is time-consuming and costly for initial design phase. Here the feasibility of predicting hydrodynamics of high-speed planing hull both with and without step using computational fluid dynamics (CFD) with the volume of fluid (VOF) methodology is studied in this work. First the flow around the prismatic body is analyzed, the force generated and its center of pressure are compared with available experimental and empirical data from the literature. The wake behind the transom on the keel line as well as the quarter beam buttock line are then compared with the available data, this is important since the afterbody flow of stepped hull is subjected from the wake of the forebody. Finally the calm water performance prediction of a conventional planing hull and its stepped version is then analyzed. Overset mesh methodology is employed in solving the dynamic equilibrium of the hull. The resistance, trim, and heave are then compared with the experimental data. The resistance is found to be predicted well and the dynamic equilibrium solved by the numerical method is deemed to be acceptable. This means that computational fluid dynamics will be very useful in further study on the complex flow around stepped hull and its potential usage in the design phase.

Keywords: planing hulls, stepped hulls, wake shape, numerical simulation, hydrodynamics

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1 Non-Reacting Numerical Simulation of Axisymmetric and Single Cavity Trapped Vortex Combustors

Authors: Heval Serhat Uluk, Sam M. Dakka

Abstract:

In this study, non-reacting simulations of axisymmetric and single cavity trapped vortex combustors were simulated to investigate the pressure drop and drag for various cavity aspect ratios and air mass flow rates. Models were validated by using experimental papers that are already available in the literature. Numerical study of axisymmetric trapped vortex combustor was carried out by using two-dimensional and three-dimensional computational domains, whereas single cavity trapped vortex combustor will only be simulated for the three-dimensional computational domain. A grid independence study will be conducted for each model. A comparison study was conducted between Reynolds Averaged Navier Stokes (RANS) k-ε Realizable with enhanced wall treatment and RANS k-ω Shear Stress Transport (SST) models to find the most suitable turbulence model, and it was found that the k-ω Shear Stress Transport model gives relatively close results to experimental outcomes. The two-dimensional model has already proven that simulation results are relatively close to the experimental results. Pressure drop rises with increasing air mass flow rate, and the lowest pressure drop was observed at 0.6 forebody/cavity aspect ratio for various air mass flow rates, which is similar to experimental outcomes. At the end of this study, it is expected to conclude the effect of air mass flow rate and cavity aspect ratio on the aerodynamics of vortex inside the cavity and find the lowest pressure drop and drag for both experimental setups. Moreover, it will also help to choose which turbulence model to use for two-dimensional and three-dimensional computational domains.

Keywords: computational fluid dynamics, aerodynamic, aerospace, propulsion

Procedia PDF Downloads 14