Measuring Parameters for a Hybrid Rocket Injector Assembly

[Wasure]

TL;DR Summary

I'm interested in just getting your ideas about the best way to measure parameters based on the ones that I want to find and how the parameter I want to find is useful

I am interested in research on hybrid rocket technology and I would like to know if anyone has a known ideal way to measure the required parameters to find the below items. I am particularly interested in a cold flow test involving:

Characteristics of the Oxidizer Flow
Turbulent Intensity
Discharge Coefficient

I am not finding a lot on cold flow. Most of the tests involve combustion or simulation whereas I would like to perform the experiment.

 

[Twigg]

What kind of equipment have you got? This sounds pretty intense. I don't know much about rockets but if you say more about your setup I might be able to help with discharge coefficient measurement. Not a flippin clue as to turbulent intensity though (unless you can do some hefty hefty numerics).

 

[Wasure]

I can use hot wire anemometry to measure turbulent intensity. It should be a decent and manageable method. I think the only drawback to it might be the response time. I'm actually not too sure how knowing this can be useful.

Would it even be practical to measure it using cold flow?I can use PIV for measuring the characteristics of the oxidizer flow. I believe obtaining this parameter is related to the fuel regression rate, combustion stability, and overall performance?

I'm mostly confused about discharge coefficient. I understand the math, with the discharge coefficient Cd = the mass flow rate divided by the density times the volumetric flow rate. I just know it has something to do with pressurizing the cold flow and obtaining the mass flow rate from that. Maybe weighted difference can be taken using load cells?

I'm also not sure about the extent of information that can be found by knowing the discharge coefficient.

I'm actually quite unfamiliar with most gadgets. I guess I can work with anything that is not super expensive or has any intensive programming required.

 

[Twigg]

The coefficient of discharge is just an empirical fudge factor that tells you how much flow you should really expect versus theory. For example, most venturi flowmeters have a discharge coefficient around 99%, meaning the real world flow rate is 99% of what you'd expect using textbook fluid mechanics (Bernoulli equation, namely).

Load cells are helpful if your mass flow rate times measurement time is larger than the measurement uncertainty of the load cells. Worth a try. You will also need pressure gauges before the nozzle and at the throat of the nozzle to know the theoretical flow rate. Depending on the dimensions, that could be tricky and it might well make performance worse by adding structure at the throat. Alternatively, you can contact the manufacturer for a discharge coefficient.

 

[Wasure]

Well, that's one question down on how discharge coefficient is useful, but would the manufacturer know the discharge coefficient if I designed the injector plate assembly on my own by just estimating ideal parameters based on other injector plate assemblies that have performed well?

I guess most people would probably just use CFD, but I'm trying to maintain an experimental approach.

 

[Twigg]

Welp, in that case the manufacturer is you! Foiled again!

Again, not versed in rockets, so I got to ask, is the flow in the nozzle expected to have a significantly high Mach number? If so, you might also need a temperature sensor before the nozzle in addition to the gauges. That combined with the mass flow rate should be enough to solve for the stagnation state I think.

 

[Wasure]

I will need to collect the temperature as well

I have not started yet, but I do know that the flow will be fast since I will be using pressure around the range of 500 psi.