Khaled S. Abdol-Hamid

Investigation of Supersonic Jet Plumes Using an Improved Two-Equation Turbulence Model

Supersonic jet plumes were studied using a two-equation turbulence model employing corrections for compressible dissipation and pressure-dilatation. A space-marching procedure based on an upwind numerical scheme was used to solve the governing equations and turbulence transport equations. The computed results indicate that two-equation models employing corrections for compressible dissipation and pressure-dilatation yield improved agreement with the experimental data. In addition, the numerical study demonstrates that the computed results are sensitive to the effect of grid refinement and insensitive to the type of velocity profiles used at the inflow boundary for the cases considered in the present study.

Computational Investigation of Circular-to-Rectangular Transition Ducts

The objective of this article is to demonstrate the feasibility of conducting three-dimensional Navier-Stokes calculations for a family of three short circular-to-rectangular transition ducts, and to establish quantitative measures of accuracy for duct design applications. A three-dimensional multiblock Navier-Stokes code, PAB3D, was used in this study. The transition ducts were designed to connect a typical circular engine exhaust to a high aspect ratio rectangular supersonic nozzle. The transitional cross sections were represented by superellipses. The rectangular supersonic nozzle was included in the flow path for the numerical analysis such that the computed results can be directly compared to existing experimental results for these ducts. Internal flow solutions were computed by using both laminar viscosity and a low Reynolds number two-equation k-£ turbulence modeling. Static pressure coefficient distributions, discharge coefficient, and thrust ratio quantities were calculated according to the on-design operating conditions for the nozzle. Good agreement between predicted surface static pressures and experimental data was observed. Nozzle performance was predicted to within experimental accuracy for both the laminar and the k-f solutions.

Computational analysis of vented supersonic exhaust nozzles using a multiblock/multizone strategy

NASA-Langleys PAB3D-v3 multiblock/multizone Navier Stokes code is presently used to study the behavior of the longitudinally-slotted nozzle configuration for fixed-geometry operation in supersonic cruise on the bases of high nozzle pressure ratios. The range of flow conditions encompassed nozzle pressure ratio values from 5 to 20, and freestream Mach numbers from 0 to 2.5. A large recirculation region was detected near the concave base of the nozzle, while smaller regions were located near and around the slots. In general, the discharge coefficient was predicted within 0.5 percent, and the thrust ratio within 1.5 percent, of measured values.

Prediction of internal performance for two-dimensional convergent-divergent nozzles

A three-dimensional code (PAB3D) has been under development to simulate underexpanded and overexpanded supersonic jet exhaust effects on a nonaxisymmetric nozzle/afterbody. The code is a multiblock/multizone technique solving the simplified Navier-Stokes equations. This method was applied to the solution of two nozzle configurations to verify the recent implementation of a nozzle performance calculation package. Static pressure distributions, discharge coefficient and thrust ratio quantities were calculated for on-design and off-design operating conditions for rectangular convergent-divergent nozzles with different throat designs. Approaches involved in computing the flows for these nozzles are presented. Computation of performance parameters were typically within 1 percent of experimental on-design and off-design data.

Prediction of static performance for single expansion ramp nozzles

A multiblock three-dimensional Navier-Stokes method was utilized in a two-dimensional fully implicit mode to calculate the flowfield of a single expansion ramp nozzle configuration. The code has been shown previously to be fairly accurate in predicting three-dimensional nozzle flowfields and internal performance for several axisymmetric and nonaxisymmetric geometries. A two-dimensional implementation of the method was used to reduce the resources required to obtain preliminary performance parameters of nozzle concepts. A two-dimensional description of a single-expansion ramp nozzle configuration was analyzed to verify the applicability of the Navier-Stokes code and nozzle performance package to this class of nozzles. Internal static pressure distributions, discharge coefficient and thrust ratio quantities were calculated for a range of operating conditions. Comparisons of predicted performance parameters with experimental data were within 0.5 percent for mass flow, and typically within l.5 percent for thrust ratio.

Commercial turbofan engine exhaust nozzle flow analyses using PAB3D

Recent developments of a three-dimensional (PAB3D) code have paved the way for a computational investigation of complex aircraft aerodynamic components. The PAB3D code was developed for solving the simplified Reynolds Averaged Navier-Stokes equations in a three-dimensional multiblock/multizone structured mesh domain. The present analysis was applied to commercial turbofan exhaust flow systems. Solution sensitivity to grid density is presented. Laminar flow solutions were developed for all grids and two-equation k-epsilon solutions were developed for selected grids. Static pressure distributions, mass flow and thrust quantities were calculated for on-design engine operating conditions. Good agreement between predicted surface static pressures and experimental data was observed at different locations. Mass flow was predicted within 0.2 percent of experimental data. Thrust forces were typically within 0.4 percent of experimental data.