Thrust Losses in Hypersonic Engines Part 1: Methodology

The engineering design and analysis of air-breathing propulsion systems relies heavily on zero-or one-dimensional properties (e.g. thrust, total pressure recovery, mixing and combustion efficiency, etc.) for figures of merit.The extraction of these parameters from experimental data sets and/or multi-dimensional computational data sets is therefore an important aspect of the design process. A variety of methods exist for extracting performance measures from multi-dimensional data sets. Some of the information contained in the multi-dimensional flow is inevitably lost when any one-dimensionalization technique is applied. Hence, the unique assumptions associated with a given approach may result in one-dimensional properties that are significantly different than those extracted using alternative approaches. The purpose of this effort is to examine some of the more popular methods used for the extraction of performance measures from multi-dimensional data sets, reveal the strengths and weaknesses of each approach, and highlight various numerical issues that result when mapping data from a multi-dimensional space to a space of one dimension.

Section: Conserved Mass/energy/entropy Methodsmentioning

confidence: 99%

Section: One-dimensionalization Techniquesmentioning

confidence: 99%

Extraction of One-Dimensional Flow Properties from Multidimensional Data Sets

Baurle

Gaffney

2008

“…The mass-averaged total pressure on which this measure is based, however, inherently does not satisfy the conservation laws. The following parameter based on the stream-thrust-averaged total pressure [13,14] (denoted as p 0 ST A ) is additionally introduced to quantify the total pressure loss, while accounting for the mass, momentum and energy on the slice plane from the three-dimensional solutions:…”

Section: Total Pressure Recoverymentioning

confidence: 99%

Physical Insight into Fuel/Air Mixing with Hypermixer Injectors for Scramjet Engines

Ogawa

Kodera

2015

Ecient mixing of fuel and air is a major objective for the successful operation of scramjet engines, where the supersonic combustion process must occur within an extremely short time frame in the hypersonic ight. This paper presents the insights gained into the key design factors and underlying mechanism for fuel/air mixing enhancement with streamwise vortices introduced by alternating wedges called hypermixers. The results of a parametric numerical study and sensitivity analysis suggest that: Narrow spanwise intervals between the alternating wedges and large fuel/air equivalence ratios are benecial for eective mixing, while higher total pressure recovery is associated with shallower ramp angles and lower fuel/air equivalence ratios.Higher fuel penetration is achieved with steeper ramp angles and higher fuel/air equivalence ratios. Streamwise vortex circulation increases with wider spanwise spacing and steeper ramp angles, but eective mixing enhancement is observed only in the latter case.

“…When portions of the propulsion system involve losses and irreversible generation of entropy, the efficiency is reduced, and the reduction in performance (specific thrust) can be directly related to the irreversible entropy increase. 1 The entropy rise occurring during premixed combustion in a flowing gas has a minimum component caused by the energy release and the chemical reactions, and an additional, irreversible, component caused by the finite velocity and, in the case of a detonation, the leading shock wave.…”

Section: Role Of Irreversibility In Steady-flow Propulsionmentioning

confidence: 99%

“…Because entropy production is detrimental to the efficiency of propulsion systems, 1 optimizing a propulsion system means minimizing the overall entropy generation in the flow. The entropy increment associated with the combustion process is often the largest of all increments through the propulsion system.…”

Section: Introductionmentioning

confidence: 99%

Stagnation Hugoniot Analysis for Steady Combustion Waves in Propulsion Systems

Wintenberger

Shepherd

2006

The combustion mode in a steady-flow propulsion system has a strong influence on the overall efficiency of the system. To evaluate the relative merits of different modes, we propose that it is most appropriate to keep the upstream stagnation state fixed and the wave stationary within the combustor. Because of the variable wave speed and upstream stagnation state, the conventional Hugoniot analysis of combustion waves is inappropriate for this purpose. To remedy this situation, we propose a new formulation of the analysis of stationary combustion waves for a fixed initial stagnation state, which we call the stagnation Hugoniot. For a given stagnation enthalpy, we find that stationary detonation waves generate a higher entropy rise than deflagration waves. The combustion process generating the lowest entropy increment is found to be constant-pressure combustion. These results clearly demonstrate that the minimum entropy property of detonations derived from the conventional Hugoniot analysis does not imply superior performance in all propulsion systems. This finding reconciles previous analysis of flowpath performance analysis of detonation-based ramjets with the thermodynamic cycle analysis of detonation-based propulsion systems. We conclude that the thermodynamic analysis of propulsion systems based on stationary detonation waves must be formulated differently than for propagating waves, and the two situations lead to very different results.