Theresa L. Benyo

Glenn Research Center, Cleveland, Ohio

Flow Matching Results of an MHD Energy Bypass 

System on a Supersonic Turbojet Engine Using the 

Numerical Propulsion System Simulation (NPSS) 

Environment

NASA/TM—2011-217136

August 2011

AIAA–2011–3591
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Theresa L. Benyo

Glenn Research Center, Cleveland, Ohio

Flow Matching Results of an MHD Energy Bypass 

System on a Supersonic Turbojet Engine Using the 

Numerical Propulsion System Simulation (NPSS) 

Environment

NASA/TM—2011-217136

August 2011

AIAA–2011–3591

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

42nd Plasmadynamics and Lasers Conference

sponsored by the American Institute of Aeronautics and Astronautics

Honolulu, Hawaii, June 27–30, 2011
Acknowledgments

The author wishes to thank Chris Snyder, Scott Jones, Dr. Steve Schneider and Dr. Isaiah Blankson for their unwaivering support

regarding this research effort. This work was also supported by the Hypersonics Project (Turbine Based Combined Cycle project) 

under NASA’s Fundamental Aeronautics Program.

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This work was sponsored by the Fundamental Aeronautics Program 

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2011-217136 1 

Flow Matching Results of an MHD Energy Bypass System on a 

Supersonic Turbojet Engine Using the Numerical Propulsion 

System Simulation (NPSS) Environment 

Theresa L. Benyo 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

Flow matching has been successfully achieved for an MHD energy bypass system on a supersonic 

turbojet engine. The Numerical Propulsion System Simulation (NPSS) environment helped perform a 

thermodynamic cycle analysis to properly match the flows from an inlet employing a MHD energy 

bypass system (consisting of an MHD generator and MHD accelerator) on a supersonic turbojet engine. 

Working with various operating conditions (such as the applied magnetic field, MHD generator length 

and flow conductivity), interfacing studies were conducted between the MHD generator, the turbojet 

engine, and the MHD accelerator. This paper briefly describes the NPSS environment used in this 

analysis. This paper further describes the analysis of a supersonic turbojet engine with an MHD 

generator/accelerator energy bypass system. Results from this study have shown that using MHD energy 

bypass in the flow path of a supersonic turbojet engine increases the useful Mach number operating range 

from 0 to 3.0 Mach (not using MHD) to a range of 0 to 7.0 Mach with specific net thrust range of 

740 N-s/kg (at ambient Mach = 3.25) to 70 N-s/kg (at ambient Mach = 7). These results were achieved 

with an applied magnetic field of 2.5 Tesla and conductivity levels in a range from 2 mhos/m (ambient 

Mach = 7) to 5.5 mhos/m (ambient Mach = 3.5) for an MHD generator length of 3 m. 

Nomenclature 

γ specific heat ratio for air 

ηN(a) enthalpy addition ratio of the MHD accelerator 

ηN(g) enthalpy extraction ratio of the MHD generator 

ηs(a) isentropic efficiency for the MHD accelerator

ηs(g) isentropic efficiency for the MHD generator 

πa stagnation pressure ratio of the MHD accelerator 

πg stagnation pressure ratio of the MHD generator 

πp stagnation pressure ratio of the pre-ionizer 

σ electrical conductivity 

χ fraction of MHD generator power diverted to pre-ionizer 

Ag cross sectional area of the MHD generator 

B magnetic field intensity 

Cp constant pressure specific heat 

K Faraday loading parameter 

L length of the MHD generator 

m mass flow rate of the air and fuel through the turbojet 

Mentrance Mach number at the entrance of a component 

Mexit Mach number at the exit of a component 

Pelec power output of the MHD generator 

PelecA power input into the MHD accelerator 

T0,12 stagnation temperature at the entrance of the MHD generator 
NASA/TM—2011-217136 2 

T0,14 stagnation temperature at the exit of the MHD generator 

T0,58 stagnation temperature at the entrance of the MHD accelerator 

T0,6 stagnation temperature at the exit of the MHD accelerator 

T0,entrance stagnation temperature at the entrance of a component 

T0,exit stagnation temperature at the exit of a component 

v velocity of flow 

Introduction 

The magnetohydrodynamic (MHD) energy bypass system has been proposed (Ref. 1) to provide 

benefits for aeropropulsion systems. It is anticipated that combining technology developments in 

electromagnetics, aerodynamics, and chemical kinetics may lead to a breakthrough for improving 

aerospace vehicle performance. A growing interest is evident in plasma-based aerodynamics including 

flow manipulation through MHD forces, power generation, and drag reduction. An integrated combined 

cycle propulsion system incorporating turbomachinery and MHD can be used in both aircraft and 

aerospace planes. One aspect of incorporating MHD within turbomachinery is the fact that 

electromagnetic fields may be used to control expanding flows in high speed nozzles to augment the 

thrust generated. An MHD energy bypass system bypasses kinetic energy (in the form of electrical power) 

from the inlet stream and uses it downstream to generate thrust or reduce drag on the vehicle. This energy 

bypass is accomplished by using weak ionization of the inlet stream by an external means and MHD 

interaction with the ionized gas. The key feature of the engine lies in the additional hardware surrounding 

the jet engine. Figure 1 shows a schematic of the MHD energy bypass system installed around a turbojet 

engine. There are three main components of an MHD energy bypass system; the pre-ionizer, the MHD 

generator and the MHD accelerator as shown in Figure 1. The additional MHD components are installed 

around an existing supersonic turbojet engine where the pre-ionizer/MHD generator pair is installed 

before the inlet and the pre-ionizer/MHD accelerator pair is installed after the nozzle of the engine. The 

following paragraphs describe the functions of each MHD component. 

MHD Pre-Ionizer 

The pre-ionizer for the MHD generator ionizes the flow coming into the MHD generator and is 

positioned downstream of the supersonic turbojet engine’s inlet. There are many methods of ionizing the 

airflow such as high voltage nanosecond discharge, fast ionization wave array, and seeding the airflow with 

alkali metals. The resulting ionized flow in conjunction with an applied magnetic field provides the benefits 

of flow control. The pre-ionizer for the MHD accelerator is positioned downstream of the supersonic 

turbojet engine’s nozzle and operates in a similar manner as the pre-ionizer for the MHD generator. 
NASA/TM—2011-217136 3 

MHD Generator 

The MHD generator towards the front of the engine acts as a flow control device and provides power 

to the pre-ionizers and MHD accelerator. The electromagnetic fields produced by the MHD generator are 

used to enable variable inlet flow control that is similar to that controlled by variable geometry. The MHD 

generator is a non-obstructing means of total temperature reduction that can be controlled by applied 

magnetic fields, conductivity levels, length of the generator, and load parameter adjustment. The MHD 

generator may be employed in the inlet, nozzle, and another duct, individually and in combination. The 

possibility of electromagnetically extracting part of the turbojet inlet air kinetic energy is the key feature. 

The concept potentially offers variable inlet geometry performance without the complexity of moving 

inlet parts. 

MHD Accelerator 

Most of the electrical power generated by the MHD generator is bypassed to the MHD accelerator at the 

back of the engine. As a result, the MHD accelerator is able to accelerate the flow exiting the engine by 

applying electromagnetic forces to the ionized flow and works together to augment the thrust generated. 

Benefits of MHD Energy Bypass 

Two primary aeropropulsion purposes are served by the MHD energy bypass concept described here. 

Firstly, flow enthalpy into the combustor is reduced allowing more efficient addition of energy in the 

combustor without exceeding temperature limitations on the turbine materials. Secondly, electrical power 

removed can be used for various on-board vehicle requirements including plasma flow control around the 

vehicle. In addition, the expanding flow in the high-speed nozzle may also be augmented by 

electromagnetic forces to generate more thrust. In order to achieve this interaction, the air needs to be 

ionized by an external means even up to fairly high flight speeds, and the leading candidates may be 

classified as electrical discharge devices. 

The generation of energy from the engine gaseous working fluid involves conversion of the thermal 

and kinetic energy of the fluid, and, therefore, gives rise to a change in both the gas temperature and 

pressure, in addition to velocity (and Mach number). Considering the possibility of subsonic and 

supersonic flow speeds along the gas flowpath in different cases and locations, the geometry of the 

flowpath becomes a significant parameter in the design and performance estimation of the generator. 

These considerations obviously also arise during input of energy back to the working fluid, whether to 

accelerate it and derive thrust output, or simply to add thermal energy to it. 

The work performed with this analysis will contribute to the following goals: 

1. Cycle Analysis—Conduct cycle analyses to establish the operating conditions for a jet engine 

cycle that are optimal for kinetic energy transfer from inlet air to a downstream location in the 

engine. 

2. Flowpath Design—The geometry of a flowpath operating from Mach 0 to Mach 7 is to be 

determined. The resulting thermodynamic efficiency is to be determined using electrical 

conductivity, magnetic field, and MHD energy conversion as some of the parameters. 

Numerical Propulsion System Simulation 

To achieve flow matching between the MHD components and a supersonic turbojet engine, a 

comprehensive thermodynamic cycle analysis environment is needed. Previous work (Ref. 2) in flow 

matching provided preliminary results for MHD energy bypass on a supersonic turbojet engine and 

showed that MHD energy bypass is a viable technique for expanding the operating envelope of a 

supersonic turbojet engine. The Numerical Propulsion System Simulation (NPSS) (Refs. 3 and 4) created 
NASA/TM—2011-217136 4 

at NASA Glenn Research Center is one such environment that can properly match the flows between all 

the elements (inlet, compressor, burner, turbine, nozzle, etc.) of an aeropropulsion system. NPSS can 

realistically model the physical interactions that take place throughout an aeropropulsion engine, 

accelerating the concept-to-production development time and reducing the need for expensive full-scale 

tests and experiments. 

NPSS is structured in a way that allows an object oriented approach of simulating aeropropulsion 

systems. Due to the complex interactions between the engine components as well as large changes in 

environmental operating conditions, computer codes are required to predict the performance of all but the 

most simple, ideal engine. NPSS is one such code and its object-oriented nature enables nearly any 

conceivable engine architecture to be modeled accurately. One such example of a turbojet engine 

architecture (Ref. 5) is illustrated in Figure 2. Each grey box and each white box represents an element 

within NPSS. A grey box indicates the element is an actual engine component and a white box indicates 

the beginning, ending, or performance conditions of the NPSS propulsion system being modeled. The 

links connecting the grey and white boxes represent the connection within NPSS that passes the flow 

conditions from one element to the next. The FS labels represent the name of each flow station. The 

remaining link types represent a fuel port connection or a shaft port connection. For instance, in Figure 2, 

the power matching between the high pressure compressor (HPC) and the high pressure turbine (HPT) is 

achieved by the ShaftPort connection and the HP_Shaft element. Likewise, the fuel supplied to the burner 

is achieved by the FuelIn element and the FuelPort connection between the two elements. The PERF 

element contains the engine performance parameters such as thrust, net thrust, ram drag, etc. 

The NPSS environment is essentially textfile-based. The text is broken down into three main 

categories; creation of objects, assignment of values to variables, and commands. The following list of 

files illustrates an example of those required for successful operation within NPSS: 

1. turbojet.mdl—this file configures the engine and runs the simulation 

2. turbojet_HPC.map—this file contains the compressor performance map 

3. turbojet_HPT.map—this file contains the turbine performance map 

4. turbojet.view_page—this file determines the format of the output 

5. turbojet.output—this is the output file generated by running the simulation 

The next section of the paper describes how the flow matching was achieved for a supersonic turbojet 

engine using an MHD energy bypass system. 
NASA/TM—2011-217136 5 

1-D Thermodynamic Equations for MHD Energy Bypass 

The goal of this analysis is to achieve flow matching between the MHD energy bypass system and a 

supersonic turbojet engine and show that a supersonic turbojet engine can theoretically operate at all 

ambient Mach numbers between Mach 0 and Mach 7. In order to achieve this goal, the NPSS 

environment is chosen since it can model the thermodynamic cycle analysis of a turbojet engine. Also, 

since NPSS is object oriented and modular, additional components modeling the behavior of all the MHD 

components can be created within NPSS and wrapped around an existing NPSS supersonic turbojet 

engine. This analysis uses a supersonic turbojet engine model previously developed by Christopher 

Snyder (Ref. 6) (NASA Glenn Research Center) within the NPSS environment and uses a new NPSS 

object within that model called DuctMHD. The new NPSS object created by the author and Mr. Snyder is 

a computer code used for simulating the MHD energy bypass system; the pre-ionizers, the MHD 

generator and the MHD accelerator. The equations that are coded within the new NPSS object, DuctMHD 

are described below. 

The enthalpy extraction ratio is determined by the output power produced by the MHD generator and 

the enthalpy input through the “inlet” of the MHD generator. The MHD generator extracts kinetic energy 

from the incoming flow ionized by the pre-ionizer positioned in front of the MHD generator. The 

calculation of this extracted kinetic energy, Pelec, is shown in the following equation derived by 

S.N.B. Murthy et al. (Ref. 7) 

1  g LAKKBvP 22

elec (1)

where the loading parameter, K = 0.5 for maximum power output in a Faraday generator. Thus, the 

enthalpy extraction ratio, ηN(g), is calculated as follows: 

 

12,0

14,012,0

entrance,0

elec

T

TT

TCm

P

p

gN

    (2) 

This value is the ratio of the extracted electrical energy and the enthalpy at the inlet of the MHD 

generator. Therefore, the stagnation (total) temperature at the exit of the pre-ionizer is modeled by adding 

a small portion of the extracted enthalpy back into the flow and is calculated as follows: 

  gN

T

T

  1

entrance,0

exit,0 (3) 

In the traditional manner, the stagnation pressure ratio of the pre-ionizers is calculated as shown here 

(Ref. 8) (Heiser, Eq. 2-114) which assumes a constant static pressure energy addition process. 

































   

1

exit,0

2 entrance,0

entrance 1

2

1 1

T

T

p M (4) 

The exit temperature of the MHD generator can also be computed using the enthalpy extraction ratio 

since energy is taken out of the flow. 

     TT 12,014,0 1  gN (5) 

 
NASA/TM—2011-217136 6 

The stagnation pressure ratio for the MHD generator (Ref. 9) is 

 

 

1

1



























gs

gN

g (6) 

where 90 percent isentropic efficiency (ηs(g) = 0.9) is assumed. Because the MHD generator extracts 

energy, the MHD accelerator takes that energy and uses it to add more energy to the flow. Hence, there is 

a temperature increase calculated as 

Cpm

P TT 

elecA

58,06,0  (7) 

where PelecA is the energy used by the MHD accelerator that is bypassed from the MHD generator. The 

energy is a percentage of Pelec and is expressed as: 

   21  elecA PP elec (8) 

where for this analysis, 10 percent of the power that is bypassed is used for both pre-ionizers (χ = 0.05 or 

5 percent of power is used for each). Thus, 90 percent of the electrical power extracted from the ionized 

flow at the MHD generator stage is transferred to the MHD accelerator. The stagnation pressure ratio for 

the MHD accelerator (Ref. 9) is expressed as 

    1 1 



a  asaN (9) 

where the enthalpy addition ratio is the amount of heat added into the flow at the MHD accelerator and is 

calculated as follows: 

  58,0

58,06,0

58,0

elecA

T

TT

TCm

P

p

N a

    (10)

MHD Energy Bypass Modeled Within the NPSS Environment 

All of the above equations were coded up and are part of the new NPSS object class called 

DuctMHD. The equations are used to model the physics of the MHD components; the pre-ionizers, MHD 

generator and MHD accelerator. The new MHD objects within NPSS were tested in a standalone mode 

(without any other type of NPSS objects connected to them) to verify the expected operation of each 

MHD component. In addition, the provided supersonic turbojet engine model in the NPSS environment 

was studied and runs were made without the additional MHD energy bypass system to obtain a baseline 

of results. Four additional NPSS objects; the pre-ionizer before the MHD generator, the MHD generator, 

the pre-ionizer before the MHD accelerator and the MHD accelerator were then installed around the 

turbomachinery objects of the supersonic turbojet engine NPSS model. 

The schematic of the NPSS objects for this new supersonic turbojet engine model is illustrated in 

Figure 3. Note that the pre-ionizer before the MHD generator is located after the exit stage of the inlet and 

the pre-ionizer/MHD generator combination is located before the high pressure compressor. Likewise, the 

pre-ionizer before the MHD accelerator is located after the low pressure turbine and the pre-ionizer/MHD 

accelerator combination is located before the nozzle of the new supersonic turbojet engine. This 

arrangement allows the pre-ionizer/MHD generator combination to condition the flow seen by the 
NASA/TM—2011-217136 7 

fan/compressor stage of the engine and bypass the extracted energy to the pre-ionizer/MHD accelerator 

combination before the nozzle stage of the engine. In reality, there may be no need to dismantle the 

existing turbojet’s nozzle and re-assemble it on the supersonic turbojet engine that has a MHD energy 

bypass system. However, an additional nozzle located at FS_6 in Figure 3 may be needed in addition to 

the new MHD components for this type of engine to be feasible. 

In order to expand the operating range of a supersonic turbojet engine from a 0 to 3 Mach range to a 

0 to 7 Mach range, the engine must be “tricked” into thinking it is flying at Mach 3 conditions. In order to 

do this, enough heat needs to be taken out of the flow before the fan stage (labeled FS_14 in Fig. 3). An 

iterative approach within NPSS, involving the exit total temperature of the MHD generator and conductivity 

levels, determined that with a 2 Tesla applied magnetic field and a MHD generator length of 3 m, an ionized 

flow of less than 10 mhos/m was needed to withdraw enough heat to allow the NPSS model to converge 

(i.e., successfully execute with no errors) at ambient Mach numbers above Mach 3. The analysis was driven 

by varying the conductivity of the ionized flow to get the desired temperature decrease at the compressor 

stage and resulted in an expanded operating range of 0 to 7 Mach. At higher Mach numbers, however, it was 

found that instead of lowering the total temperature at stage FS_14 all the way down to 600 K, it was 

lowered to a higher total temperature in order to successfully run the engine cycle. 

MHD Energy Bypass Turbojet Cycle Flow Matching Results 

An NPSS cycle analysis with the model depicted in Figure 3 was conducted in order to determine the 

basic geometry and electromagnetic conditions (length, flow area, applied magnetic field, and 

conductivity levels) required for the MHD components installed on a supersonic jet engine. It was also 

desired to demonstrate successful operation of this MHD energy bypass turbojet cycle on a full range of 

Mach numbers from Mach 0 to Mach 7. Both of these goals were met with this analysis. 

The following operating parameters were studied that resulted from the NPSS cycle analysis. 

1. Conductivity levels 

2. Power extracted from ionized flow 

3. Enthalpy extraction/addition ratios 

4. Total and static pressures 

5. Total and static temperatures 

6. Gross thrust, net thrust, specific net thrust 

 
NASA/TM—2011-217136 8 

The data of most interest will be presented here. The focus at present is on the specific net thrust of 

the resulting MHD turbojet compared to the original turbojet and the total pressures and total temperature 

profiles throughout the flow path of the supersonic turbojet engine with and without the MHD energy 

bypass system. 

Conductivity Levels 

Figure 4 shows the conductivity levels needed in order for the NPSS cycle analysis to fully operate 

between Mach 3.25 and Mach 7.0 for the MHD energy bypass components installed on a supersonic 

turbojet engine with an MHD generator length of 3 m. Multiple runs were made with a range of applied 

magnetic fields from 1 to 5 Tesla. However, at the 1 Tesla level, the conductivity levels are higher than 

reasonably practical with a top value of almost 35 mhos/m. Even at the 2 Tesla level, the highest 

conductivity level is almost 10 mhos/m. Figure 4 shows the conductivity levels for applied magnetic 

fields of 2.5 to 5 Tesla. Notice that the levels are kept under 5.5 mhos/m which is a reasonable maximum 

limit as indicated by previous research (Ref. 10). 

Extracted Electrical Power 

Figure 5 shows the actual amount of electrical power extracted from the ionized flow at the MHD 

generator stage of the supersonic turbojet engine with MHD energy bypass installed in megawatts of 

power. The amount of power extracted varies with ambient Mach number and has a range of 45 to 

90 MW. In this model, 90 percent of the extracted electrical energy is used by the MHD accelerator and 

the pre-ionizers each use 5 percent of the extracted energy. 
NASA/TM—2011-217136 9 

It is interesting to note that the amount of energy extracted varies widely particularly between 

ambient Mach = 4.75 and 7. Between ambient Mach = 4.75 and 5.25, the amount of power extracted 

(Pelec) increases linearly which is due to the fact that while ݉ሶ and ηN(g) remain constant at ~10 kg/s and 

~50 percent respectively, the value of T0,12 increases from 1180 to 1380 K. On the other hand, Pelec

decreases linearly from ambient Mach = 5.25 and 6.00 mainly because ݉ሶ decreases from ~10 to ~4 kg/s. 

From ambient Mach = 6.00 to 6.75, the value of Pelec increases again because in this region, ݉ሶ increases 

from ~4 to ~5 kg/s and ηN(g) remain relatively constant at ~60 percent while T0,12 increases from 1720 to 

2089 K. 

Enthalpy Extraction/Addition Ratios 

The percent of the amount of electrical energy extracted out of the flow within the MHD generator is 

indicated in Figure 6 for each ambient Mach number in this MHD energy bypass study. The ratio is based 

on the amount of energy needed to be extracted to allow the supersonic turbojet engine to realize Mach 3 

conditions for the engine’s burner. Note that the percent extracted from the ionized flow varies between 

10 and 60 percent. Figure 7 shows the enthalpy addition ratio of the MHD accelerator. Here, the ratios 

vary between 2 and 38 percent. It is interesting to note that both ratios generally increase as ambient 

Mach number increases. 
NASA/TM—2011-217136 10 

Total Temperature 

Figures 8 and 9 show the total temperatures at each flow station in the supersonic turbojet model. 

Figure 8 shows the results of the runs without the MHD generator and MHD accelerator. The NPSS 

model does not run to convergence after reaching an ambient Mach of 3.75. Hence, only runs of ambient 

Mach 3 to Mach 3.75 are shown. Notice that until flow station FS_2 (exit stage of the duct before the high 

pressure compressor), the temperature stays fairly constant and from flow station number FS_2 to FS_4, 

there is a large increase in total temperature. These flow stations are located between the compressor and 

the high pressure turbine. This of course is to be expected as the turbojet’s burner exit is located at station 

FS_4. The main objective here is to show the performance of the supersonic turbojet engine without 

MHD energy bypass and to achieve the same or nearly the same performance at higher Mach numbers 

with MHD energy bypass. 

 
NASA/TM—2011-217136 11 

Figure 9 shows the total temperature from the inlet to the exit of the nozzle of the supersonic jet engine 

model with MHD energy bypass. Notice that there is a temperature decrease from station Fs_12 to Fs_14 on 

all cases. These stations are located before and after the MHD generator. This is also to be expected since 

the MHD generator works to draw out energy from the weakly ionized flow and thus lowers the 

temperature. Not all cases were able to decrease the total temperature at FS_14 (MHD generator exit) to the 

desired value of 600 K. This value of total temperature is what is achieved for the ambient Mach = 3.0 

instance without MHD energy bypass and is considered the design point of the engine. At higher ambient 

Mach numbers (Mach 5 and greater), a higher total temperature at FS_14 is needed in order to have the 

engine cycle run successfully and produce positive specific thrust. These total temperatures ranged from 

650 K (Mach 5) to 930 K (Mach 7). In addition, the total temperature increases from flow station FS_56 to 

FS_6 where the MHD accelerator is located. The energy bypassed from the MHD generator shows up as a 

total temperature increase at the MHD accelerator. Overall, the results in Figure 9 are very similar to those 

in Figure 8 with the exception of the ambient stage (FS_a) and the MHD accelerator nozzle stage (FS_6 and 

FS_7). These results mean that the MHD energy bypass is an effective tool for enabling a supersonic jet 

engine to fly at higher Mach numbers (from Mach 3.25 to Mach 7.0). 

Total Pressure 

Figures 10 and 11 show the total pressures at each flow station in the supersonic turbojet model. 

Figure 10 shows the results of the runs from Mach 3 to Mach 3.75 without the MHD energy bypass 

system. These are the highest ambient Mach number cases that run to convergence. As expected, the 

increase in total pressure happens through the high pressure compressor (FS_2) with peak pressure at 

FS_3 and the total pressure decreases through the turbine (FS_5). 

 
NASA/TM—2011-217136 12 

Comparing this to Figure 11, one can see that the total pressure is somewhat suppressed from FS_2 to 

FS_5 on cases Mach 3.5 and above as compared to the case operating without MHD. This suppression is 

due to the MHD energy bypass system and the result of extracting out a rather substantial amount of 

energy from the ionized flow. At the higher ambient Mach numbers (greater than Mach 4.0), the total 

pressure losses are particularly high. This is due to the fact that more kinetic energy is extracted out (40 to 

60 percent) of the flow through the MHD generator in order to lower the total temperatures as compared 

to the lower ambient Mach numbers (Mach 3.25 to Mach 4.00) where 10 to 35 percent of the kinetic 

energy is extracted out of the ionized flow. Notice as well, that at ambient Mach numbers equal to and 

greater than 5.5, the total pressures at the burner are below that at sea level (101 kPa) and at this 

condition, the turbojet engine would require a special burner design to keep the burner lit and operating 

efficiently. However, the overall shape of the total pressure data from inlet to nozzle remains similar to 

the cases without MHD energy bypass suggesting that the supersonic turbojet engine with MHD energy 

bypass operates at the higher Mach numbers as it would at the lower Mach numbers without MHD energy 

bypass. 

Specific Net Thrust 

And finally, the specific net thrust of the supersonic turbojet engine with MHD energy bypass is 

shown in Figure 12. Without MHD energy bypass, the turbojet model does not run to convergence 

(i.e., execute successfully) above Mach 3.75 and the results in Figure 12 show specific net thrust results 

without MHD energy bypass from Mach 0 to Mach 3.25 because that is the normal operating range of this 

supersonic engine. Notice that the specific net thrust decreases only slightly at Mach 3.25 with MHD 

energy bypass turned “on” and positive specific net thrust is realized for all Mach numbers to the desired 

upper limit of Mach 7. As mentioned in the total temperature results section, the data in Figure 12 is 

achieved by allowing the MHD generator exit temperatures (FS_14) to increase from 600 K to a range of 

650 K (Mach 5) to 930 K (Mach 7). These specific net thrust results are comparable to previous research 

completed by the author (Ref. 11). 
NASA/TM—2011-217136 13 

Conclusions 

A supersonic turbojet engine with MHD energy bypass was modeled under the NPSS software 

environment. This software environment realistically models the physical interactions that take place 

throughout an aeropropulsion engine. The new NPSS element (DuctMHD) models the pre-ionizers, the 

MHD generator, and the MHD accelerator. Verifying the operation of DuctMHD was done with a test 

harness before installing the MHD components on a model of a supersonic turbojet engine. Normal 

operation for the supersonic turbojet model of this study is in the Mach 0 to Mach 3 range. The MHD 

components were “wrapped” around the supersonic turbojet model and runs were made without MHD 

energy bypass and with MHD energy bypass. The model ran from Mach 0 to Mach 3.75 without MHD 

energy bypass and ran from Mach 0 to Mach 7 with MHD energy bypass. The length of the MHD 

generator was kept at 3 m and a full range of applied magnetic field values from 1 to 5 Tesla were used to 

run the test cases. As a result, the case with an applied magnetic field of 2.5 Tesla offered a desired 

conductivity level range from 2 mhos/m to no more than 5.5 mhos/m. The range of electrical power 

extracted from the ionized flow of the MHD generator was found to be between 45 and 90 MW which 

translated to between 10 and 60 percent of the energy being extracted. The MHD accelerator used 

90 percent of the extracted power which when added back, results in an enthalpy addition ratio, ηN(a), 

between 2 and 38 percent back into the flow. The specific net thrust from these runs enabled positive 

values from 740 N-s/kg (at ambient Mach = 3.25) to 70 N-s/kg (at ambient Mach = 7). 

Results from this study confirm that operating a supersonic turbojet in the Mach 0 to Mach 7 range is 

indeed possible provided that MHD energy bypass is installed on the engine. MHD technology can be a 

valuable addition to hypersonic flight in that it can expand the operating conditions of existing turbojet 

engines such as the supersonic turbojet engine studied in this analysis. This cycle analysis helps establish 

the operating conditions for a jet engine cycle that are optimal for kinetic energy transfer from inlet air to 

a downstream location in the engine. Further study will need to be done in order to determine a cost 

benefit ratio for MHD energy bypass as well as in sizing an engine with MHD energy bypass to the 

vehicle requirements to determine its feasibility in meeting the thrust requirements. 
NASA/TM—2011-217136 14 

References 

1. Blankson, I.M., S. Schneider, “Hypersonic Engine Using MHD Energy Bypass With a Conventional 

Turbojet,” presented at the 12th AIAA International Space Planes and Hypersonic Systems and 

Technologies, December 2003, AIAA–2003–6922. 

2. Benyo, T.L., “Initial Flow Matching Results of MHD Energy Bypass on a Supersonic Turbojet 

Engine Using the Numerical Propulsion System Simulation (NPSS) Environment,” June 2010, 

AIAA–2010–4301. 

3. Claus, R.W., Evans, A.L., Lytle, J.K., Nichols, L.D., “Numerical Propulsion System Simulation,” 

Computing Systems in Engineering, Vol. 2, No. 4, pp. 357–364, 1991. 

4. “NPSS User Guide: Software Release: NPSS_1.6.5,” Numerical Propulsion System Simulation 

NASA Industry Cooperative Effort, March 12, 2008. 

5. Jones, S.M., “An Introduction of Thermodynamic Performance Analysis of Aircraft Gas Turbine 

Engine Cycles Using the Numerical Propulsion System Simulation Code,” NASA/TM—2007-

214690, March 2007. 

6. Snyder, C., “A White Paper on the development and validation of a thermodynamic model of the 

F135 for Fundamental Aeronautics Projects Hypersonics,” unpublished NASA GRC white paper, 

Cleveland, OH, September 30, 2007. 

7. Murthy, S.N.B and I.M. Blankson, “MHD Energy Bypass Turbojet-Based Engines,” presented at the 

51st International Astronautical Congress, October 2000, Rio de Janeiro, Brazil, IAF-00-5-5-05. 

8. Heiser, W.H. and D.T. Pratt with D.H. Daley and U.B. Mehta, Hypersonic Airbreathing Propulsion, 

AIAA Education Series, AIAA, Washington, D.C., 1994, pp. 77–81. 

9. Litchford, R.J., J.W. Cole, V.A. Bityurin, J.T. Lineberry, “Thermodynamic Cycle Analysis of 

Magnetohydrodynamic-Bypass Hypersonic Airbreathing Engine,” NASA/TP—2000-210387. 

10. Schneider, S.J., “Annular MHD Physics for Turbojet Energy Bypass,” April 2011, AIAA–2011–

2230. 

11. Benyo, T.L., “The Effect of MHD Energy Bypass on Specific Thrust for Supersonic Turbojet 

Engine,” January 2010, AIAA–2010–0232. 
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Flow Matching Results of an MHD Energy Bypass System on a Supersonic Turbojet Engine 

Using the Numerical Propulsion System Simulation (NPSS) Environment 

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Benyo, Theresa, L. 

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14. ABSTRACT

Flow matching has been successfully achieved for an MHD energy bypass system on a supersonic turbojet engine. The Numerical 

Propulsion System Simulation (NPSS) environment helped perform a thermodynamic cycle analysis to properly match the flows from an 

inlet employing a MHD energy bypass system (consisting of an MHD generator and MHD accelerator) on a supersonic turbojet engine. 

Working with various operating conditions (such as the applied magnetic field, MHD generator length and flow conductivity), interfacing 

studies were conducted between the MHD generator, the turbojet engine, and the MHD accelerator. This paper briefly describes the NPSS 

environment used in this analysis. This paper further describes the analysis of a supersonic turbojet engine with an MHD 

generator/accelerator energy bypass system. Results from this study have shown that using MHD energy bypass in the flow path of a 

supersonic turbojet engine increases the useful Mach number operating range from 0 to 3.0 Mach (not using MHD) to a range of 0 to 7.0 

Mach with specific net thrust range of 740 N-s/kg (at ambient Mach = 3.25) to 70 N-s/kg (at ambient Mach = 7). These results were 

achieved with an applied magnetic field of 2.5 Tesla and conductivity levels in a range from 2 mhos/m (ambient Mach = 7) to 5.5 mhos/m 

(ambient Mach = 3.5) for an MHD generator length of 3 m.

15. SUBJECT TERMS

Magnetohydrodynamic simulation; Thermodynamics; Jet thrust; Supersonic turbojet 

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